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  • Process optimization and magnetic properties of soft magnetic composite cores based on phosphated and mixed resin coated Fe powders
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-21
    Kaili Li; Danni Cheng; Hongya Yu; Zhongwu Liu

    Fe powders based soft magnetic composites (SMCs) with organic- inorganic multiple-layer coating were fabricated by improved isolation coating followed by pressing and curing. Phosphate and organic resin were selected as the insulting layers. The influences of phosphating process and the composition of organic coating on the magnetic properties of the SMCs and soft magnetic cores have been systematically investigated. The phosphating process was modified for simple and easy operation, suitable for carbonyl iron powders with small particle size. The optimized phosphating method created a complete and continuous phosphate layer on the surface of micron sized particles. Without resin coating, the magnetic cores fabricated with the phosphated powders prepared with 0.5 - 0.7 wt.% phosphoric acid exhibit relatively high permeability and quality factor at high frequency. In addition, a new type of mixed resin with good thermal stability was employed for insolating coating, which provides distinctly higher resistivity and better protective effect than silicone. The optimal content of the mixed resin content is about 3 wt.% for fabricating the magnetic cores with low eddy current loss and hysteresis loss by producing a protective layer to isolate magnetic particles and reduce the internal stress. The SMC cores prepared with optimized phosphating process and organic coating exhibit high relative density (93.7%), high electric resistivity (2.23×107 Ω·cm), stable permeability (in the frequency range from 5 – 1000 kHz), high quality factor (44.8 at 700 kHz) and relatively low magnetic loss (159.0 kW/m3 at 100 kHz).

    更新日期:2020-01-21
  • Pressure-induced magnetic phase transitions of intermetallic Fe2AlB2
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Sezgin Aydin; Mehmet Şimşek

    Pressure-dependent magnetic properties and magneto-structural phase transitions of the intermetallic Fe2AlB2 compound have been investigated by using spin-polarized density functional theory calculations. From the enthalpy calculations, possible phase transitions are predicted. It is seen that a phase transition from ferromagnetic (FM) to antiferromagnetic (AFM) occurs at 40 GPa, and the other one is from AFM to nonmagnetic (NM) occurs at 96 GPa. To investigate the source of the magneto-structural phase transitions, atomic bonding characteristics, and possible pressure effects on the physical properties of the compound are calculated. And, the structural, electronic, and mechanical properties of FM-, AFM- and NM-phases are considered as a function of pressure on the 0-120 GPa range. Subsequently, the spin-polarized partial and total density of states (DOS), projections of the charge densities, integrated spin densities, magnetization (or net magnetic moment), DOSs at the Fermi level, Mulliken bond overlap populations are studied to present a compact pressure analysis for Fe2AlB2. It is observed that there are sudden changes and discontinuities in the structural and magnetic properties at 40, 54, 59, and 96 GPa pressures as well as the other physical properties, which support the magneto-structural phase transitions.

    更新日期:2020-01-21
  • Computation of current waveform in ferrite power inductors for application in buck-type converters
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Carlo Ragusa; Luigi Solimene; Salvatore Musumeci; Olivier de la Barriere; Fausto Fiorillo; Giulia Di Capua; Nicola Femia

    In this paper we propose a calculation model for the analysis of the current waveform in ferrite power inductors subjected to large-signal square-wave voltage, a typical regime of present-day switch-mode power supplies. This kind of problem is characterized by the non-linear response of the inductor across a wide range of current values, up to the limit of inductor saturation. Consequently, non-linear differential equations must be adopted in the description of the circuit. In this paper, we solve the equations of the circuit through an effective iterative method, by which the current waveform is computed through successive approximations. These results are eventually verified by comparison with experiments performed on a commercial buck-type converter.

    更新日期:2020-01-21
  • Comprehensive analysis of direct and converse magnetoelectric effects in S-S mode bilayered composites
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Xiaoli Zhang; Jian-Ping Zhou; Xi Yao; Zupei Yang; Guang-Bin Zhang

    There are few experimental studies on the shear-shear (S-S) mode magnetoelectric (ME) composites, especially near the resonance frequency because of their complex sample preparation and high resonance frequency. What’s more, theoretical studies on the S-S mode magnetoelectric composites is still blank. In this article, an equivalent circuit model was proposed to analyze the direct and converse magnetoelectric (DME and CME) effects in an S-S mode ME bilayered composite. Then, the composite was experimentally studied, showing a good agreement with the theoretical predication. The S-S mode has a remarkable field sensitivity and much high DME and CME coefficients, reaching 27.5 V/(cm·Oe) and 3×10-6 s/m, respectively, in this simple bilayered composite under the DC magnetic field of 1800 Oe near the resonance frequency. The composite shows a prospect of applications in high frequency ME transducers, energy capture devices and magnetic field sensitive sensors.

    更新日期:2020-01-21
  • Interfacial Tm3+ moment-driven anomalous Hall effect in Pt/Tm3Fe5O12 heterostructure
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Yu Kuai Liu; Hon Fai Wong; Sheung Mei Ng; Chee Leung Mak; Chi Wah Leung

    We performed anomalous Hall effect (AHE) measurements in Pt/Tm3Fe5O12 (Pt/TmIG) bilayers grown on (110) and (111)-oriented Gd3Ga5O12 (GGG) substrates (Pt/110TmIG and Pt/111TmIG). Qualitative differences were observed in the two sets of samples: at low magnetic fields only Pt/111TmIG displays square AHE loop, while Pt/110TmIG exhibits non-hysteretic AHE behavior. Systematic temperature-dependent AHE measurements in Pt/111TmIG showed double switching events of AHE loops below 30 K, which was attributed to the larger moment of Tm3+ sublattice at low temperature and was consistent with earlier theoretical calculations [A. Lehmann-Szweykowska et al., Phys. Rev. B 37, 459 (1988)]. Our results confirmed the strong coupling of magnetic moment of Tm3+ with the lattice and the crucial role of the interfacial structure, suggesting a way to detect the rare earth moment switching in iron garnets by electrical measurements.

    更新日期:2020-01-21
  • Naked-eye visualization of geometric frustration effects in macroscopic spin ices
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    R.S. Gonçalves; A.C.C. Gomes; R.P. Loreto; C.I.L. de Araujo; F.S. Nascimento; W.A. Moura-Melo; A.R. Pereira

    We study planar rectangular-like arrays composed by macroscopic dipoles (magnetic bars with size around a few centimeters) separated by lattice spacings a and b along each direction. Physical behavior of such macroscopic artificial spin ice (MASI) systems are shown to agree much better with theoretical prediction than their micro- or nano-scaled counterparts, making MASI ”almost ideal prototypes” for readily naked-eye visualization of geometrical frustration effects.

    更新日期:2020-01-21
  • Magnetic anisotropy in Cr2GeC investigated by X-ray magnetic circular dichroism and ab initio calculations
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Martin Magnuson; Maurizio Mattesini

    The magnetism in the inherently nanolaminated ternary MAX-phase Cr2GeC is investigated by element-selective, polarization and temperature-dependent, soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The measurements indicate an antiferro-magnetic Cr-Cr coupling along the c-axis of the hexagonal structure modulated by a ferromagnetic ordering in the nanolaminated ab-basal planes. The weak chromium magnetic moments are an order of magnitude stronger in the nanolaminated planes than along the vertical axis. Theoretically, a small but notable, non-spin-collinear component explains the existence of a non-perfect spin compensation along the c-axis. As shown in this work, this spin distortion generates an overall residual spin moment inside the unit cell resembling that of a ferri-magnet. Due to the different competing magnetic interactions, electron correlations and temperature effects both need to be considered to achieve a correct theoretical description of the Cr2GeC magnetic properties.

    更新日期:2020-01-21
  • A millimeter-wave Bell Test using a ferrite parametric amplifier and a homodyne interferometer
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-20
    Neil A. Salmon; Stephen R. Hoon

    A combined ferrite parametric amplifier and millimeter-wave homodyne interferometer are proposed as an ambient temperature Bell Test. It is shown that the non-linear magnetic susceptibility of the yttrium iron garnet (YIG) ferrite, on account of its narrow line-width Larmor precessional resonance, make it an ideal material for the creation of entangled photons. These can be measured using a homodyne interferometer, as the much larger number of thermally generated photons associated with ambient temperature emission can be screened out. The proposed architecture may enable YIG quantum technology-based sensors to be developed, mimicking in the millimeter-wave band the large number of quantum optical experiments in the near-infrared and visible regions which had been made possible by use of the nonlinear beta barium borate ferroelectric, an analogue of YIG. It is illustrated here how the YIG parametric amplifier can reproduce quantum optical Type I and Type II wave interactions, which can be used to create entangled photons in the millimeter-wave band. It is estimated that when half a cubic centimeter of YIG crystal is placed in a magnetic field of a few Tesla and pumped with 1 Watt of millimeter-wave radiation, approximately 1012 entangled millimeter-wave photon pairs per second are generated by the spin-wave interaction. This means an integration time of only a few tens of seconds is needed for a successful Bell Test. A successful demonstration of this will lead to novel architectures of entanglement-based quantum technology room temperature sensors, re-envisioning YIG as a modern quantum material.

    更新日期:2020-01-21
  • Novel Fe-based amorphous and nanocrystalline powder cores for high-frequency power conversion
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-18
    Kenny L. Alvarez; H.A. Baghbaderani; J.M. Martín; N. Burgos; M. Ipatov; Z. Pavlovic; P. McCloskey; A. Masood; J. Gonzalez

    The present work demonstrates the high-frequency core loss performance of Fe-based amorphous and nanocrystalline powder cores, initially produced by gas atomised powder, consolidated using sieved particles ≤ 20 µm, and isolated by a precise insulating layer of polymer to limit the inter- and intra-particle eddy currents to attain enhanced performance. The large glass forming ability (GFA) of the gas atomised powder, reflected by different glass forming instruments, such as the supercooled region (ΔTX = 54 °C) and the reduced glass transition temperature (Trg= 0.56), is consistent with the substantial amorphisation capability of the alloy. To the best of our knowledge, this is the first-ever report to reveal a large ΔTX in the Finemet-type alloy powders, an essential parameter to gas-atomise the amorphous powders with significantly lower cooling rates compared to the melt-spun ribbons. Further, subsequent annealing of the amorphous powders, between the exothermic events guided by differential scanning calorimetry (DSC), lead to the growth of a fine nanocrystalline structure of grains ≤ 15 nm, thanks to the positive enthalpy of mixing of Cu with the constituents to act as a nucleation agent, to retain the excellent soft magnetic properties. The DC soft magnetic properties of the powders were significantly improved on thermal annealing, confirmed by hysteretic loops, quantified by reduced coercivity HC < 1 Oe of annealed powder at < 575 °C, and attributed to the reduced magnetoelastic contribution due to zero/near-zero magnetostriction anisotropy, attained due to the homogenous nanocrystalline structure. The amorphous and nanocrystalline powder cores, consolidated by compression moulding, show ultra-high loss performance, due to the ultra-low coercivity attained on nanocrystallisation, and negligible eddy currents loss, owning to efficient insulation of small particles, for high-frequency power conversion applications, such as voltage regulator (VR), and resonant converters, in automotive industry and data storage centres.

    更新日期:2020-01-21
  • Broadband and high-sensitivity permeability measurements on a single magnetic particle by transformer coupled permeameter
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-18
    S. Tamaru; N. Kikuchi; T. Igarashi; S. Okamoto; H. Kubota; S. Yoshida

    We have developed a system to measure permeability over a wide frequency range with high sensitivity, which we call the transformer coupled permeameter. In this system, the magnetic sample is sandwiched by two short-terminated coplanar waveguides that form a loosely coupled transformer. In this way, the stimulus signal acting as a background becomes smaller as the frequency decreases, thus significantly suppressing the deterioration of the signal-to-noise ratio (SNR) at low frequencies that most conventional permeameters suffer from. It has been demonstrated that this system can provide a sensitivity high enough to measure the permeability of a single ferromagnetic flake particle comprising a noise suppression sheet over 10 MHz-20 GHz with a high SNR.

    更新日期:2020-01-21
  • Magnetic dipole localization and magnetic moment estimation method based on normalized source strength
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-18
    Gang Yin; Ping Li; Zhi Wei; Gang Liu; Zhenhua Yang; Li Zhao

    Based on the virtue of complete isotropy around a dipole source, the normalized source strength (NSS) is introduced to the scalar triangulation and ranging (STAR) method to replace the original tensor contraction and a new real-time magnetic dipole localization method without asphericity error is proposed in this paper. Firstly, three unknown parameters of bearing vector are estimated by solving the equations about the NSS of six faces of the magnetometer cube. Secondly, the magnitude of magnetic moment vector is estimated using NSS and magnitude of the estimated bearing vector. Thirdly, linear equations about three unknown parameters of unit magnetic moment vector are established using the intermediate eigenvalues and NSS of six faces of the cube, and the least square solution is given. Simulations without and with measurement noises have been done to evaluate the performance of the proposed method. The results show that the proposed algorithm is correct in theory and the estimation results are more accurate than two other improved STAR methods.

    更新日期:2020-01-21
  • Complex Permittivity, Complex Permeability and Reflection Loss of Co-Zr substituted La-Sr Hexaferrites in 18 – 40 GHz frequency range
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-18
    Pawandeep Kaur; S. Bindra Narang; Shalini Bahel

    In this research, electromagnetic and microwave absorption properties of the hexagonal ferrites with chemical composition, Sr0.85La0.15(CoZr)xFe12-2xO19 (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were studied in the K-band (18 – 26.5 GHz) and Ka-band (26.5 – 40 GHz) frequency range. Minimum reflection loss (RL) was successfully optimized in the studied frequency range by tuning sample thickness using quarter-wavelength criterion. Absorption results of synthesized hexagonal ferrites show minimum RL in the range of -18.15 dB to -28.69 dB and absorption bandwidth (-10 dB) in the range of 1.04 GHz to 5.87 GHz. The microwave absorption significantly improved with absorption bandwidth (-10 dB) of 5.87 GHz for the composition x = 1.00 at a sample thickness of 2.2 mm. These newly synthesized ferrites have high potential as microwave absorbing material for military applications such as camouflaging of the target and also as EMI (Electromagnetic Interference) suppressor.

    更新日期:2020-01-21
  • Study of magnetic and magneto-transport properties of nanocrystalline Nd0.5Ca0.5MnO3 compound: Observation of large magnetoresistance
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    Kalipada Das; Snehal Mandal; Snehal Mandal; Pintu Sen; I. Das

    Magnetic and magneto-transport properties of nanocrystalline Nd0.5Ca0.5MnO3 compound are presented. In contrast to its bulk counterparts, with modification of the magnetic grounds state, large magnetoresistance appeared in the presence of comparatively lower magnetic field in nanocrystalline compound. Additionally, the magnetic field induced insulator-metal transition took place in nanocrystalline compound with negligible thermal hysteresis. From application perspectives, observation of the low field magnetoresistance in this compound may be important for several uses in magnetic field sensor related technology. Fundamentally, the influences of the ferromagnetic phase fraction as well as the induced ferromagnetic interaction in nanocrystalline samples on magnetic and magneto-transport properties were addressed.

    更新日期:2020-01-21
  • Magnetotransport in under and optimally hole-doped bulk nanocrystalline La1-xCaxMnO3 manganites
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2019-12-14
    Yugandhar Bitla; P.D. Babu; S.N. Kaul

    Electrical-transport and magneto-transport in bulk nanocrystalline (BNC) La1-xCaxMnO3+δ (x = 1/8 with either δ = 0.00 or δ = 0.06, x = 3/8 with δ = 0.00) (LCMO) manganite system have been studied treating the bulk crystalline (BC) counterparts as the reference systems. Irrespective of the value of δ in under hole-doped (x = 1/8) LCMO, the metal-insulator (M-I) transition (not observed in the BC counterpart) appears at a temperature TMI ≪ TC, where TC is the temperature at which the ferromagnetic (FM) - paramagnetic (PM) second-order phase transition occurs. Oxygen off-stoichiometry makes the M-I transition more pronounced and reduces the overall magnitude of resistivity. Reducing the average crystallite size d below 150 nm, lowers both TMI and TC in the BNC samples with x = 1/8 and δ = 0.00 or 0.06 but decreases TMI while increasing TC in the optimally hole-doped x = 3/8 LCMO. The single-orbital double-exchange model, which predicts the coincidence, or otherwise, of the M-I and FM-PM transitions with some success in the BC LCMO, fails to correctly describe the above-mentioned results in BNC LCMO. The resistivity minima at low temperatures (Tmin), completely absent in BC, occur in BNC LCMO, regardless of the value of x,δ,d and the strength of the magnetic field (H). The mechanism for resistivity, ρ(T), changes from the adiabatic small polaron nearest-neighbor hopping (for x = 3/8) or from the Shklovskii-Efros variable range hopping, SE-VRH, (for x = 1/8), prevalent in BC, to the Mott-VRH in the PM insulating state in the BNC counterparts when d falls below 150 nm. At T < Tmin, the contributions due to the Mott-VRH (present only in the samples with x = 1/8 and δ = 0.00 or δ = 0.06) and the enhanced electron-electron Coulomb interaction (in all the BNC LCMO samples) are responsible for the negative temperature coefficient of resistivity (TCR). By contrast, the coherent electron-magnon scattering accounts for the positive TCR observed at T > Tmin. H suppresses the mean hopping energy difference between the hopping sites but increases the electron localization length. The field-induced enhancement in the localization length far outweighs the field-induced drop in the mean hopping energy difference to produce an increase in the mean hopping distance with H.

    更新日期:2020-01-21
  • Impact of strontium substitution on the structural, magnetic, dielectric and ferroelectric properties of Ba1-xSrxFe11Cr1O19(x = 0.0–0.8) hexaferrites
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    M. Atif; M. Hanif Alvi; S. Ullah; Atta Ur Rehman; M. Nadeem; W. Khalid; Z. Ali; H. Guo

    Strontium substituted barium hexaferrites i.e., Ba1-xSrxFe11Cr1O19 with x = 0.0–0.8 were prepared via co-precipitation technique. Single-phase magnetoplumbite structure was confirmed for all samples by X-ray diffraction, whereas scanning electron microscopy showed the variation in microstructure on Sr2+ substitution. Magnetic measurements revealed that the substitution causes prominent enhancement in saturation magnetization and coercive field for x = 0.4 sample. However, under same condition, decrease in real part of dielectric permittivity, dielectric loss tangent and ac conductivity were observed by impedance spectroscopy, while these parameters started to increase for x > 0.4. The dielectric permittivity exhibited frequency-dependent dispersive behavior due to Maxwell-Wagner interfacial polarization whereas weak ferroelectric hysteresis loops were obtained for the prepared samples. Moreover, it was found that the Sr2+ substitution substantially enhanced the resistive properties which is elucidated in term of localization of charge carrier’s mobility due to reduction in Fe3+-O-Fe2+ network and microstructural variations. Here, it is proposed that x = 0.4 sample exhibits maximum magnetization (64 emu/g), moderate real part of dielectric permittivity at low frequency (>103), diminished dielectric loss tangent (~0.05) and colossal value of resistance (~1010 Ω) which makes this material interesting for high frequency applications.

    更新日期:2020-01-17
  • Loss decomposition in plastically deformed and partially annealed steel sheets
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-17
    F.J.G. Landgraf; C. Ragusa; D. Luiz Rodrigues Junior; M.B.S. Dias; O. de la Barrière; F. Mazaleyrat; F. Fiorillo; C. Appino; L. Martino

    There is an increasing interest in the optimization of non-oriented electrical steels for applications under excitation frequencies above 400 Hz. We discuss in this paper the possibility of a new manufacturing procedure, where skin-pass and subsequent heat treatment for recovery are applied as the two last stages of sheet processing. Samples from a commercial non-oriented 3 wt% silicon steel were submitted to 2.5% thickness reduction and were heat treated at temperatures ranging between 600 and 850 °C for 2 hours. It is shown that, although the hysteresis loss increases with plastic deformation, the excess loss decreases in such a way that under increasing magnetizing frequencies the total energy loss of the deformed and recovered sample becomes lower than in the starting material. The higher the annealing temperature the lower the frequency at which crossover of the loss curves is observed, as long as full recrystallization does not occur. It is assumed that with the dislocation structures left in the deformed and partially recovered samples one achieves a condition of increased fragmentation of the magnetization process, that is, of increased number of concurring correlation regions (Magnetic Objects). The corresponding decrease of the excess loss component can eventually overcompensate the deterioration of the quasi-static magnetic properties, leading to lower total losses.

    更新日期:2020-01-17
  • Performance of transverse magneto-optical Kerr effect in double-positive, double-negative and single-negative bi-gyrotropic metamaterials
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-16
    Mansoureh Amanollahi; Mehdi Zamani

    The properties of optimized transverse magneto-optical Kerr effect (TMOKE) of all-types of bi-gyrotropic metamaterials have been investigated and compared for both s- and p-polarized waves. We demonstrated that double-positive and double-negative ones are capable of achieving maximum TMOKEs, but with the opposite signs. On the other hand, single-negative metamaterials could not provide large TMOKE. In addition, a giant TMOKE can be observed in a special case of metamaterials whose are exhibiting near-zero refractive index. A large TMOKE response is important for applications in magneto-optical data storage and high-definition imaging.

    更新日期:2020-01-17
  • In-situ studies of magnetostriction in TbxHo1-xFe1.9Mn0.1 Laves compounds
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-16
    M.K. Wang; J.J. Liu; Q.L. Ding; Y. Xiao; R.B. Jiao; Z.B. Pan; W.X. Xia; J.P. Liu

    The magnetic domain structure and magnetostrictive properties of TbxHo1-xFe1.9Mn0.1compounds have been investigated by in-situ Lorentz transmission electron microscopy (LTEM). The magnetocrystalline anisotropy compensation has been realized to be around x = 0.12 based on the easy magnetization direction (EMD) and by evaluating magnetocrystalline anisotropy constant K1, magnetization and magnetostriction. The EMD at room temperature rotates from the <100> axis for x ≤ 0.10 to <111> axis for x ≥ 0.12, which is detected directly by electronic holography technique. The magnetic domain wall movements were observed by in-situ magnetic field LTEM, and the critical magnetic field Hcr decreases continuously from 100 Oe for the Tb-rich side of x = 0.16 to 60 Oe for the Tb-poor side of x = 0.12, owing to the decrease in magnetocrystalline anisotropy subjected by anisotropy compensation. A high low-field magnetostriction (λa∼200 ppm at 1 kOe) is achieved at the critical magnetocrystalline anisotropy compensation point of x = 0.12. This work helps to understand the correlation between magnetocrystalline anisotropy, magnetization process, magnetic domain wall motion and magnetostriction in the C15 Laves phase system.

    更新日期:2020-01-17
  • Structural and Magnetic Properties of P25 TiO2 Nanoparticles Doped by Co
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-15
    José F.M.L. Mariano; Valentim G. Bessergenev; João P. Lourenço; Martin Hantusch; Eberhard Burkel; Ana M. Botelho do Rego; Michal Rajňák; Milan Timko; Peter Kopčanský

    The present work reports on the structural and magnetic properties of TiO2 P25 Degussa powder doped with cobalt. Dissolution of cobalt in TiO2 matrix was achieved by precipitation of tris(diethylditiocarbamato) cobalt(III) (CoDtc - Co[S2CN(C2H5)2]3 in chloroform (CHCl3) and consequent thermal treatment. Five different Co atomic percentage contents were chosen, e.g., 0.5%, 1%, 2%, 5% and 10%. It was shown that cobalt atoms are uniformly distributed across TiO2 matrix and exhibit antiferromagnetic interactions at low temperatures.

    更新日期:2020-01-15
  • Microscopic Characteristics of Magnetorheological Fluids Subjected to Magnetic Fields
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-15
    Ningning Wang; Xinhua Liu; Shuaishuai Sun; Grzegorz Królczyk; Zhixiong Li; Weihua Li

    With the aim of studying the microscopic characteristics of a magnetorheological fluid (MRF) in a magnetic field, the theoretical analyses of the particles dynamics in a magnetic field are presented, and a model for the particle motion is proposed. Based on these analyses, a three-dimensional numerical simulation of the microstructure of MRFs in different magnetic fields is performed. Furthermore, the microstructures of the MRFs are investigated using industrial computed tomography (CT) imaging. The numerical simulation and industrial CT results indicate that the chain structure of the same MRF becomes more apparent as the magnetic field strength increases, and in the same external magnetic field, this chain structure also becomes more apparent with an increase in the particle volume fraction. The lengths of particle chains in different magnetic fields are also captured in the industrial CT experiments. When the magnetic field strength is 12 mT, the particle chains of the MRF with a particle volume fraction of 30% reach more than 10 mm in length, which bridge the inner diameter of the container, and the dense clusters-like structure is formed, the clusters-like structure becomes denser with an increase in magnetic field. Moreover, the particle chain lengths of MRF with high particle volume fractions increase sharply with the magnetic field. The experiments demonstrated that the industrial CT is an efficient method to study the microstructures of MRFs by providing particle distributions of MRFs more clearly and intuitively.

    更新日期:2020-01-15
  • Magnetic Semiconductor Properties of RbLnSe2 (Ln = Ce, Pr, Nd, Gd): A Density Functional Study
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-14
    Lahcene Azzouz; Mohamed Halit; Zoulikha Charifi; Hakim Baaziz; Michel Rérat; Hassan Denawi; Chérif F. Matta
    更新日期:2020-01-14
  • 更新日期:2020-01-14
  • Tracking the Suhl instability versus angle and frequency for the backward volume mode in an yttrium iron garnet film
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-14
    Jinho Lim; Wonbae Bang; Jonathan Trossman; C.C. Tsai; John B. Ketterson

    Using parametric excitation, we have studied the minimum frequency associated with the backward volume (BV) spin wave branch in a thin film of the ferrimagnetic material yttrium iron garnet for the magnetic field lying in plane and parallel to the wave vector as well as for out-of-plane field angles. We find that there is a drastic change in the efficiency of parametric excitation between two different pumping frequency regimes.

    更新日期:2020-01-14
  • 更新日期:2020-01-14
  • Design and preparation of an ultrathin broadband metamaterial absorber with a magnetic substrate based on genetic algorithm
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    Benfang Duan; Junming Zhang; Peng Wang; Guowu Wang; Donglin He; Liang Qiao; Tao Wang

    High-efficiency microwave absorption materials are widely used in electronic equipment and communication facilities. This study aims to develop a broad-bandwidth metamaterial absorber based on the magnetic substrate with a central frequency selective surface (FSS). It is however, different from the strategy of expanding the bandwidth for metamaterial absorbers reported in other literatures, in this study, a unique development strategy that involves selecting the most suitable magnetic substrate from a database using genetic algorithm is adopted. By adding an optimized FSS layer to the magnetic substrate, its loss performance and impedance matching performance are considerably improved, and the resulting metamaterial absorber exhibits excellent absorption properties. At a thickness of 3.1 mm, the reflection loss in the range from 2.5 to 17.2 GHz is below –10 dB, which is significantly better than the values reported in previous studies. In addition, the prepared metamaterial absorber possesses excellent absorption characteristics under oblique incidence conditions. The strategy proposed in this study leads to the successful development of a high-efficiency metamaterial absorber and represents a more effective approach than those previously used in the field.

    更新日期:2020-01-14
  • Magnetic structures in the locally inverted interlayer coupling region of a bilayer magnetic system
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    Chanki Lee; Hee Young Kwon; Nam Jun Kim; Han Gyu Yoon; Chiho Song; Doo Bong Lee; Jun Woo Choi; Young-Woo Son; Changyeon Won

    We use a Monte Carlo simulation to investigate the magnetic structures in a bilayer magnetic system containing a locally inverted interlayer coupling region. The stabilization of multiple magnetic structures, including the magnetic skyrmion, is possible in the locally inverted interlayer coupling region. Various factors such as the region area, anisotropy, interlayer coupling strength, and exchange coupling strength affect the properties of the structures, including their size and chirality. We obtain conditions for the stabilization and transitions of these magnetic structures. The Dzyaloshinskii-Moriya interaction (DMI) and dipolar interaction play prominent roles as they significantly enhance the formation and stability of the structures. An asymmetric feature can arise from the broken inversion symmetry in the structure formation, yielding an interfacial DMI, which stabilizes the skyrmion. It is demonstrated that the dipole interaction also acts as an effective interfacial DMI in the system.

    更新日期:2020-01-14
  • Measuring FORCs diagrams in computer simulations as a mean to gain microscopic insight
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    A.B. Dobroserdova; P.A. Sánchez; V.E. Shapochkin; D.A. Smagin; V.S. Zverev; S. Odenbach; S.S. Kantorovich

    FORCs (first-order reversal curves) diagrams prove to be an efficient experimental technique to investigate magnetic interactions in complex systems. In experiments, as a rule, it is difficult to relate actual microstructural changes to the evolution of FORCs diagrams. Here, using Molecular Dynamics simulations, we calculate FORCs for two simple models of a magnetic elastomer. The simplicity of these models allows to relate directly both, the rigidity of the matrix and the magnetoelastic coupling to the shape and intensity of FORCs diagrams.

    更新日期:2020-01-13
  • Structural Characterization Of Concentrated Aqueous Ferrofluids
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    A.V. Nagornyi; V. Socoliuc; V.I. Petrenko; L. Almasy; O.I. Ivankov; M.V. Avdeev; L.A. Bulavin; L. Vekas

    Structure characterizations of concentrated water-based magnetic fluids stabilized by oleic and lauric acids were done by means of small-angle neutron scattering (SANS) and complemented by dynamic light scattering and magnetization analysis. Stability of ferrofluids with time against sedimentation was concluded despite the presence of aggregates in solutions. Differences in the average sizes of individual polydisperse magnetite nanoparticles coated with surfactants and their aggregates were revealed. Structural parameters obtained from SANS have been confirmed by magnetogranulometry data. The comparative analysis of the aggregation and its change upon dilution is made basing on the data of SANS and dynamic light scattering techniques.

    更新日期:2020-01-13
  • Brillouin-Mandelstam Spectroscopy of Stress-Modulated Spatially Confined Spin Waves in Ni Thin Films on Piezoelectric Substrates
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    Fariborz Kargar; Michael Balinskiy; Howard Chiang; Andres C. Chavez; John Nance; Alexander Khitun; Gregory P. Carman; Alexander A. Balandin

    We report the results of micro-Brillouin-Mandelstam light scattering spectroscopy of thermal magnons in the two-phase synthetic multiferroic structure consisting of a piezoelectric [Pb(Mg1/3Nb2/3)O3](1-x) –[PbTiO3]x (PMN-PT) substrate and a Ni thin film. The experimental data reveal the first two modes of the perpendicular standing spin waves (PSSW) spatially confined across the Ni thin film. A theoretical analysis of the frequency dependence of the PSSW peaks on the external magnetic field reveals the asymmetric boundary condition, i.e. pinning, for variable magnetization at different surfaces of the Ni thin film. The strain field induced by applying DC voltage to PMN-PT substrate leads to a downshift of PSSW mode frequency owing to the magneto-elastic effect in Ni, and corresponding changes in the spin-wave resonance conditions. The observed non-monotonic dependence of the PSSW frequency on DC voltage is related to an abrupt change of the pinning parameter at certain values of the voltage. The obtained results are important for understanding the thermal magnon spectrum in ferromagnetic films and the development of the low-power spin-wave devices and quantum sensors.

    更新日期:2020-01-13
  • Proximity effect tuned magnetic properties in composites of carbon nanotubes and nanoparticles of CoFe2O4
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-13
    H. Verma; T. Mekuria; P. Seck; H. Hong; S.P. Karna; D. Seifu

    The saturation magnetization of composites of carbon nanotubes and CoFe2O4 (CFO) magnetic nanoparticles synthesized through a novel one-step process in the presence of a surfactant (sodium dodecyl-benzene-sulfonate) show significant increase, to 208 emu/g. This value of saturation magnetization of the composite is a factor of 3.3 higher than pristine CFO nanoparticles. This is the first time such a remarkable magnetic behavior of CFO/ carbon nanotubes composite is presented. The increased magnetism is attributed to the proximity effect between uniformly distributed ferromagnetic CFO nanoparticles on the surface of carbon nanotubes and hybridization of the π-electronic states of carbon and the 3d-bands of CFO. Scanning electron microscopy images confirm uniform and dense distribution of CFO nanoparticles on carbon nanotubes. Magnetic force microscopy images confirm the formation of uniformly distributed magnetic stripe domains. The sample was characterized at ambient using X-ray diffraction, Raman Spectroscopy, atomic force microscopy, scanning electron microscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy. Magnetic properties were characterized by magnetic force microscopy and magnetometry using vibrating sample magnetometer.

    更新日期:2020-01-13
  • Magnetocaloric effect in molecular spin clusters and their assemblies: Exact and Monte Carlo studies using exact cluster eigenstates
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    Sumit Haldar; S. Ramasesha

    Frustrated magnetic molecules are promising alternatives to refrigerant materials for low temperature magnetic refrigeration. We investigate the magnetocaloric effect (MCE) in un-frustrated and frustrated spin clusters formed from spin chains of six sites, with site spins s=1,3/2 and 2 possessing site diagonal anisotropies and anisotropic exchange interactions, using exact diagonalization method. We also study MCE in spin clusters, on a chain, a 2-D square lattice and a 3-D cubic lattice with spin-dipolar interactions by a Monte Carlo method in spin-1 systems which uses exact eigenstates of a cluster. The magnetocaloric effect is closely related to the magnetic Grüneisen parameter ΓH. In this paper, we compute the magnetic Grüneisen parameter ΓH, and study its dependence on exchange anisotropy and spin-dipolar interaction. With increase of exchange anisotropy, the maxima in ΓH shifts to higher magnetic fields and becomes a sharp singularity. The singularities in ΓH correlate with cusps in the entropy as a function of magnetic field strength, and with crossover in the magnetization in the ground state in isolated clusters. The first maximum in ΓH shifts to lower fields as we increase spin-dipolar interaction. The first maximum in ΓH also shifts to lower magnetic field strength as the magnitude of the site spin increases. We show the dependence of ΓH on the dimensionality of the lattice for a fixed lattice constant.

    更新日期:2020-01-13
  • Correlating magnetic properties of ferritic NO electrical steel containing 2.4m.%Si with hot strip microstructure
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    A. Stoecker; N. Leuning; K. Hameyer; X. Wei; G. Hirt; S. Korte-Kerzel; U. Prahl; R. Kawalla

    Understanding the interdependencies of the processing steps of high silicon containing non-oriented (NO) electrical steel is a key factor for improving its final magnetic properties. Moreover, every process step in the production has a significant impact on the properties. Steels with a high silicon content are ferritic (α-Fe). Accordingly, the microstructure and texture are inherited from one processing step to the next. The presented research relates the hot strip microstructure and texture to the magnetic properties of the final annealed material. To investigate the impact of hot strip microstructure and texture for a ferritic 2.4m.%Si silicon containing steel, the material was hot rolled from an initial thickness of 64mm down to a thickness of 1mm whereby different microstructures and textures were achieved by varied hot rolling conditions. Subsequently, the material was cold rolled to 0.25mm and annealed at 800°C or 1000°C for 3min. Finally, samples of each processing step were analyzed by means of light microscopy and XRD texture measurements. Samples after hot rolling and final annealing were tested in a single sheet tester for specific losses and magnetic polarization. Findings show an influence of the initial hot strip microstructure on the microstructure and magnetic properties of the final annealed samples.

    更新日期:2020-01-13
  • Spin-orbit torques in antiperovskite Fe4N pseudo-single-crystal films with negative spin polarization
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    Shinji Isogami

    The spin-orbit torque (SOT) damping-like (field-like) effective fields and efficiencies, HDL(FL) and ξDL(FL), for the MgO substrate/Fe4N (3 nm)/W (5 nm)/cap metallic heterostructure were determined using harmonic Hall and spin-Hall magnetoresistance (SMR) measurements at various temperatures (T). The resistivity of the W layer was measured to be 40 μΩ cm, suggesting a mixed phase of α and β. The sizable anomalous Nernst component was extracted, and a strong T dependence was found. The resultant ξDL(FL) was estimated to be 0.035 (0.015) at T = 300 K, and 0.045 (0.005) at T = 4 K. The longitudinal MR measurements revealed the negative spin polarization of the conduction electrons in the Fe4N layer. However, no sign reversal of the SOT was observed, as in the case where a CoFeB layer with positive spin polarization was employed. The T dependence of ξDL estimated from SMR measurements was in good agreement with that obtained through harmonic Hall measurements, which was indicative of the sizable spin current injection at the Fe4N/W interfaces due to the spin-Hall effect.

    更新日期:2020-01-13
  • X-band Shielding of Electromagnetic Interference (EMI) by Co2Y Barium Hexaferrite, Bismuth Copper Titanate (BCTO), and Polyaniline (PANI) composite
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    T. Tchouank Tekou Carol; J. Mohammed; D. Basandrai; Sachin Kumar Godara; Gopala R. Bhadu; Sanjay Mishra; Neha Aggarwal; S.B. Narang; A.K. Srivastava

    Co2Y/BCTO/PANI composite was synthesized using mechanical blending method. The XRD analysis shows that the composite exhibit pure phase of Co2Y barium hexaferrites and bismuth copper titanate (BCTO) which is also supported by Raman analysis. Resonance occurs over the whole frequency region in the spectra of Co2Y/BCTO/PANI composite with dielectric losses dominating the lower frequency region due to interfacial polarization and magnetic losses dominating the higher frequency region as a result of eddy current losses, natural and exchange resonance. The observed values of shielding effectiveness for reflection are higher than those of shielding effectiveness for absorption, this indicates that most of the incident EM wave is reflected rather than absorbed. The Co2Y/BCTO/PANI composite shows total shielding effectiveness value above 20 dB with maximum total shielding effectiveness value of 31.97 dB at 10.30 GHz and matching thickness of 2 mm. The high value of total shielding effectiveness is attributed to good impedance matching between the components of the Co2Y/BCTO/PANI composite as well as higher dielectric losses as compared to magnetic loses.

    更新日期:2020-01-13
  • Resistive Switching in Strontium Iridate based Thin Films
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    Víctor Fuentes; Borislav Vasić; Zorica Konstantinović; Benjamín Martínez; Lluís Balcells; Alberto Pomar

    We report on the local electrical properties, measured by conductive atomic force microscopy (C-AFM), of the Iridate-based Srn+1IrnO3n+1 family of thin films, in particular by comparing the n=1, Sr2IrO4, and the n=∞, SrIrO3 phases. We analyze the different resistive switching behavior as a function of the pristine electronic properties of the films. We will show that, for films exhibiting insulating behavior, i.e., films of the n=1 phase or films below 3 nm of thickness for the n=∞ phase, hysteretic I-V curves with a sharp transition into a low resistance state (LRS), i.e. an abrupt increase of the current intensity, is detected above a well-defined threshold voltage. This suggests a resistive switching behavior associated to the jump between two resistance states that may be correlated to the activation energy, Δ, obtained by fitting the temperature dependence of the resistivity to a thermal activated Arrhenius law, ρ (T) ∼ ρ0exp(-Δ /kBT). On the other hand, thicker samples of the n=∞ phase exhibit a semimetallic character and I-V curves show progressive changes of the local resistance without a clearly defined threshold voltage. Kelvin Probe Force Microscopy based measurements confirmed that, concomitantly to the resistive switching, an evolution of the electronic states at the surface takes place that may be associated to the migration of oxygen vacancies promoted by the electrical fields under the AFM tip.

    更新日期:2020-01-13
  • High temperature spin cluster glass behavior in Co- and Si-substituted garnet ferrite thin films
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-11
    Hiroyasu Yamahara; Munetoshi Seki; Hitoshi Tabata

    In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (111) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co2+ and nonmagnetic ones of Si4+. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10-5. The substitution of Co2+ and Si4+ induces a chemical disorder and competing antiferromagnetic and ferromagnetic interactions, which induce a spin glass behavior. When the Co−Si substitution ratio is increased, a spin-freezing behavior is observed below the spin-freezing temperature TG = 190−220 K of the Lu3Fe4Co0.5Si0.5O12 film; this indicates the presence of a cluster glass phase. The film demonstrates a characteristic memory effects in the temperature range 120−180 K, which are below TG; this reveals the presence of a metastable magnetic state in the multi-valley energy landscape with shallow activation energy barriers. Ferromagnetic resonance measurements confirm increased perpendicular anisotropy energy induced by Co substitution and spin-wave characteristics including the inverse spin Hall effect voltage (VISHE). Lu3Fe5-2xCoxSixO12 films show an increase in damping and a decrease in VISHE at the cryogenic temperature, which are attributed to the impurity relaxation mechanism. Therefore, the Co- and Si-substituted films exhibit strong spin-wave damping at a low temperature, which reflects the spin-freezing dynamics of cluster glass behaviors.

    更新日期:2020-01-13
  • Torque in Open-access Permanent Magnet Variable Flux Sources
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    Bochen Li; Yangkun He; Chengbao Jiang; Plamen Stamenov; J.M.D. Coey

    A flux source with four rotatable permanent magnet rods with access from two perpendicular directions through gaps exceeding the rod diameter can produce a continuously-variable flux density of up to ±300 mT at the centre when high-grade Nd-Fe-B magnets are used. The trade-off between field, access and torque in this mangle design is discussed. The maximum field, achievable when the magnets touch, is equal to the remanence of the Nd-Fe-B. The torque needed to rotate the rods scales as the square of the remanence, and it increases faster than the inverse square of the separation when the separation is comparable to the rod diameter. End effects reduce the torque significantly, but appropriate gearing is needed to ensure smooth operation. Modifications of the basic design can reduce or compensate the torque by using special end pieces, and improve access to fields > 1000 mT at small rod separation

    更新日期:2020-01-10
  • Effect of tensile stress on cobalt-based amorphous wires impedance near the magnetostriction compensation temperature
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    D.A. Bukreev; M.S. Derevyanko; A.A. Moiseev; A.V. Semirov

    This study investigates the effect of tensile stress on the impedance of an amorphous Co66Fe4Ta2.5Si12.5B15 wire near the magnetostriction compensation temperature at approximately 170 K. When the wire is exposed to the tensile stress, the wire impedance modulus is found to demonstrate high temperature sensitivity of over 2%/K. This finding can help in designing of temperature sensors.

    更新日期:2020-01-10
  • Influence of spin Nernst effect on continuum spin conductivity in antiferromagnets in the checkerboard lattice
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    L.S. Lima

    The influence of the spin Nernst effect on longitudinal spin conductivity, σxx is investigated in the two-dimensional antiferromagnetic model in the checkerboard lattice and in the presence of Dzyaloshinskii-Moriya interaction employing spin waves. We present results of the influence of the Dzyaloshinskii-Moriya interaction as well as variation of the Nernst coefficient at finite temperature on continuum spin conductivity.

    更新日期:2020-01-10
  • Enhanced Microwave Absorption Properties of MnS2 Microspheres Interspersed with Carbon Nanotubes
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    Chao Liu; Bochong Wang; Congpu Mu; Kun Zhai; Fusheng Wen; Jianyong Xiang; Anmin Nie; Zhongyuan Liu

    In order to avoid the electromagnetic interference, fabricating the microwave absorber is extremely urgent. In this work, a simple and effective method was used to prepare the MnS2/CNTs (carbon nanotubes) hybridization for microwave absorption. The composite of MnCO3/CNTs was acquired by a wet chemical process, and then the hybridization was vulcanized and transformed into MnS2/CNTs hybridization. By changing the reactant concentration, the composites of MnS2/CNTs with the CNTs ratios of 5%, 10%, 12% and 15% were prepared for the microwave absorption measurement. For the MnS2/12%CNTs composite, the minimum reflection loss (RLmin) reached -63.8 dB at 17.4 GHz with a thickness of 1.4 mm. Furthermore, the maximum bandwidth (RL < -10 dB) was 4.3 GHz (from 12.9 GHz to 17.4 GHz) with the thickness of 1.6 mm. Based on the consequence, MnS2/CNTs composite is a competitive candidate as the high-frequency microwave absorber.

    更新日期:2020-01-10
  • Fe2MnSn - experimental quest for predicted heusler alloy
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-10
    M. Kratochvílová; D. Král; M. Dušek; J. Valenta; R. Colman; O. Heczko; M. Veis

    Fe2MnSn compound was prepared in the form of polycrystalline ingot by arc-melting. In contrast to the theoretical predictions of stable tetragonal Heusler compound, the material crystallizes in a hexagonal DO19 crystal structure and orders ferromagnetically below TC = 586(10) K that is only about half of the calculated value of 1012 K. Magnetic moment 5.87 μB at 10 K is less or about in line with various theoretical predictions. However, electrical resistivity and optical studies reveal no signs of half-metallic behavior predicted theoretically. The change in the slope of the MOKE spectra below 1.5 eV suggests the main influence of a low energy inter-band transition which points to the loss of half-metallicity in agreement with resistivity and optical measurements.

    更新日期:2020-01-10
  • Hyperfine Interactions in Fe/Co-B-Sn Amorphous Alloys by Mössbauer Spectrometry
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    Marcel B. Miglierini; Július Dekan; Martin Cesnek; Irena Janotová; Peter Švec; Marek Bujdoš; Jaroslav Kohout

    Hyperfine interactions in Fe78B15Sn7 metallic glass with Co/Fe substitution were investigated by Mössbauer spectrometry. As-quenched samples were prepared by planar flow casting and subsequently annealed at 673 K for 30 min which is in the region of phase transformations determined by differential scanning calorimetry. Magnetic thermogravimetry unveiled increase in Curie temperature after Co substitution. Structural analysis was performed by X-ray diffraction and transmission electron microscopy. The results show formation of primary bcc-Fe(Co) phase with proceeding nanocrystallization and indicate supersaturation of this phase with Sn. Hyperfine interactions between nuclei and electron shells were investigated by Mössbauer spectrometry at different temperatures and in external magnetic field. Modifications of the short-range order are demonstrated mainly by deviations in the positions of the net magnetic moment. They are driven by nanocrystallization as well as temperature of measurement and/or presence of external magnetic field.

    更新日期:2020-01-10
  • Magnetothermodynamic properties of frustrated pyrochlore Gd2FeSbO7 in cooperative two-sublattice molecular-field model
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    S. Nandi; Y.M. Jana; D. Chakraborty; J. Alam; P. Bag; S.S. Islam; R. Nath

    The pyrochlore, Gd2FeSbO7, having general formula unit A2B2O7, was chosen for magnetic and heat capacity study in this work due to presence of Fe3+ moments, whose 3d orbitals (3d5:3t2g3eg2) are half-filled and carry a large magnetic moment, at B site of the structure, and hence create additional Gd−O−Fe−O−Gd pathways, which result in strongly antiferromagnetic superexchange interactions among the Gd−Gd spins as well as for the Gd−Fe bonds. Gd2FeSbO7 behaves paramagnetic down to ∼10 K with effective antiferromagnetic nearest-neighbour interactions resulting negative Curie-Weiss temperature, θCW = −12.62 K. Fe sublattice exhibits a weak ferromagnetic transition at TC ≈ 5 K. The frustration index f = |θCW|/TC becomes 2.5 indicative of moderate frustration, which may prevent Palmer-Chalker ground state configuration of Gd sublattice at lower temperature in the system. Heat capacity Cp exhibits a broad anomaly at ∼3.1 K and calculated magnetic heat capacity Cm/T attains a peak at ∼1 K, but is much weaker than for other pyrochlores Gd2B2O7 (B = Sn, Ti, Ge, Pt) which are all found to order at 1 K or lower, thereby reflecting a short-range second-order transition in Gd2FeSbO7. The nature of transition was also verified by Arrott plot of magnetization. Finally the magneto-thermodynamic data were analyzed on the basis of a cooperative two-sublattice model taking account of intra-sublattice (Gd−Gd and Fe−Fe) and inter-sublattice (Gd−Fe) magnetic interactions, defined by three molecular-field parameters, λGd−Gd = − 0.71 T/μB, λFe−Fe = 0.87 T/μB, and λGd−Fe = − 0.61 T/μB in presence of the easy-planer crystal-field anisotropy at Gd-site. Without Gd−Fe interaction, two independent interpenetrating Gd3+ and Fe3+Sb5+ sublattices can not precisely demonstrate the measured thermomagnetic properties of Gd2FeSbO7. This study thus revealed that 3d−4f magnetic interactions offer Gd2FeSbO7 a unique place in the series of gadolinium-based pyrochlores.

    更新日期:2020-01-10
  • Investigation of phonons and magnons in [Ni80Fe20/Au/Co/Au]10 multilayers
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    M. Zdunek; A. Trzaskowska; J.W. Kłos; N.K.P. Babu; S. Mielcarek
    更新日期:2020-01-10
  • Spin-reorientation transition and temperature dependence of high- frequency properties in [Co/Pd]6/Permalloy multilayer thin films
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    Yurui Wei; Chen Liu; Xiangqian Wang; Huiliang Wu; Haiyan Xia; Zhaozhuo Zeng; Jianbo Wang; Jiangwei Cao; Qingfang Liu

    High-frequency studies, of exchange-coupled multilayer films, are the key to advance the development of fast switching spintronic devices. In this paper, we utilize the first-order reversal curve (FORC) to improve the understanding of the spin-reorientation transition process when the permalloy (Py) thickness increases. We also investigate the temperature dependence of the high-frequency properties of exchange-coupled [Co/Pd]6/Py (t nm) multilayer films during the spin-reorientation transition (SRT). The results show that the phase state of the magnetic domain changes, from the perpendicular phase to the multi-domain phase as the Py layer increases during the SRT. The temperature-dependent high frequency results indicate that the resonance linewidth ΔHres increases gradually when the temperature decreases from 300K to 50K. Our experimental study offers new insight into the SRT process in exchange-coupled multilayer films and can help to promote the development of fast switching spintronic devices.

    更新日期:2020-01-10
  • In-field δM plots: simple yet efficient manner to assess interactions in exchange-bias systems
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    J. Geshev; R.F. Lopes; J.L. Salazar Cuaila; L.L. Bianchi; A. Harres

    Recently, the in-field δMR interaction-plot technique has been extended for systems with shifted and asymmetric major magnetization hysteresis loops. In the present work an alternative definition of δMR, allowing a better graphic visualization of this plot, is given. The method is applied to a series of Co/Cu/IrMn films in order to examine the variations, with the thickness of the nonmagnetic Cu layer, of the interactions emerging from the Co/IrMn interface and those coming from magnetic coupling within the Co film. Model simulations indicate that, for the case of symmetric major loops, the effects of the ferromagnet/antiferromagnet exchange coupling might not be identified by interaction plots, being only evidenced by the shift along the magnetic-field axis and the coercivity enhancement.

    更新日期:2020-01-10
  • Spin liquids and spin glasses in Mn-based alloys with the cubic A13 (β-Mn) structure
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    Rui Zhang; Zsolt Gercsi; M. Venkatesan; Ajay Jha; Plamen Stamenov; J.M.D. Coey

    As-cast ingots of Mn100-xZx with Z = Al, Ge, Mn, Fe and Co all have the A13 β Mn up to some maximum value of x. The magnetic susceptibility of pure β Mn is ≈ 9 x 10-4 from 4 – 400 K, but the field-cooled and zero-field-cooled susceptibilities of all doped samples increase at low temperature and they bifurcate at a spin-freezing temperature Tf that increases with x, linearly at first. Point contact Andreev reflection shows evidence of a net spin polarization in a spin glass sample but not in the pure β Mn spin liquid. Fixed-moment density functional calculations indicate a very shallow energy minimum (< 1 meV/atom) for 12d-site Mn moment that extends from x = 0 to 0.4 µB. The minimum energy is interpreted as a lower limit on the zero-point energy.

    更新日期:2020-01-10
  • Metallographic and Magnetic Analysis of Direct Laser Sintered Soft Magnetic Composites
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    B. Kocsis; I. Fekete; L.K. Varga

    In this present study, soft magnetic composite samples were made from iron-silicon alloys. For the purpose of optimizing 3D printing parameters, preliminary experiments were performed. Metallographic and computed tomography investigations were used to determine the appropriate sintering settings. Besides the microscopic and CT analysis, considering the permeability spectra have been compared to the samples.

    更新日期:2020-01-10
  • Crack Characterization in Ferromagnetic Steels by Pulsed Eddy Current Technique based on GA-BP Neural Network Model
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    Wang Zhenwei; Yuan fei; Pengxin Ye; Fasheng Qiu; Guiyun Tian; Wai Lok Woo

    Ferromagnetic steels are widely used in engineering structures such as rail track, oil/gas pipeline and steel hanging bridge. Cracks resulted from manufacturing processes or previous loading will seriously undermine the safety of the engineering structures and even lead to catastrophic industrial accidents. Accurate and quantitative characterization the cracks in ferromagnetic steels are therefore of vital importance. In this paper, the cracks in ferromagnetic steels are detected by the pulsed eddy current (PEC) technique. Firstly, the physical mechanism of the relative magnetic permeability of the ferromagnetic steel on the detection signal of PEC is interpreted from a microscopic level of magnetic domain wall movement. The relationship of the crack width/depth and the detection signal of PEC is then investigated and verified by numerical simulations and experimental study. Finally, the cracks are inversely characterized by using Genetic Algorithm (GA) based Back-Propagation (BP) neural network (NN) considering the nonlinearity of the crack geometric parameters with the detection signal of PEC. The prediction results indicated that the proposed algorithm can characterize the crack depth and width within the relative error of 10%. The proposed approach combining PEC and GA based BPNN has been verified to quantitatively detect cracks in ferromagnetic steel.

    更新日期:2020-01-10
  • Influence of synthesis methods with low annealing temperature on the structural and magnetic properties of CoFe2O4 nanopowders for permanent magnet application
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-09
    B. Abraime; K. El Maalam; L. Fkhar; A. Mahmoud; F. Boschini; M. Ait Tamerd; A. Benyoussef; M. Hamedoun; E.K. Hlil; M. Ait Ali; A. El Kenz; O. Mounkachi

    Cobalt ferrite nanopowders were prepared with low annealing temperatures (400 °C and 600 °C) using four different synthesis methods: co-precipitation, sol-gel, sol-gel autocombustion and microemulsion. The pure phase is obtained in all the samples and confirmed using the XRD diffraction. The crystallite size is calculated based on the XRD patterns and ranged between ∼9 nm and ∼26 nm. The SEM micrographs show an agglomeration with an increase of grain size between 400 °C to 600 °C samples for all the used methods. The magnetic properties are given. The best obtained values are MS =80,319 emu/g , HC =2057,97 Oe and (BH)max = 0.3313 MGOe for co-precipitation, sol-gel and sol-gel autocombustion, respectively. An improvement of 89% in (BH)max value is observed in the case of sol-gel auto-combustion when we go from 400 °C to 600 °C.

    更新日期:2020-01-09
  • Control of Grain Density in FePt-C Granular Thin Films During Initial Growth
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    Ippei Suzuki; Jian Wang; Yukiko K. Takahashi; Kazuhiro Hono

    Herein, we report a systematic study on the microstructure evolution of FePt-C granular films grown on MgO(001) single-crystalline substrates, especially during the initial growth stage. The number density of the grains during the nucleation stage is strongly affected by the growth temperature, reaching 40 Tgrain/in2 at <200 °C and decreasing with further increasing temperature. The addition of carbon (C) as a segregant substantially reduced the density. Despite the high number density during the nucleation stage, the density was dramatically reduced with subsequent growth of the FePt-C film. The possible reason for the reduction in the grain density is the surface diffusion of the C added to enhance grain separation. Controlling the growth conditions rather than the nucleation stage is key to increasing the areal density of FePt-C granular films to develop heat-assisted magnetic recording media.

    更新日期:2020-01-09
  • Enhancement of saturation magnetisation through the addition of a nonmagnetic element in substitutional Fe-doped In2O3 powder
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    Marzook S. Alshammari; Kadi Y. Museery; Ahmad S. Alshammari; Raja L. AL Otaibi; Ali A. Yousif; Abbasher Gismelseed; O.M. Lemine

    Iron-doped indium oxide is a promising material for spin electronics (spintronics) applications. Herein, an experimental investigation of the effect of adding a nonmagnetic element (magnesium) on the enhancement of the room-temperature ferromagnetism in substitutional iron-doped In2O3 powder was conducted. A new doping process, which avoids the formation of Fe nanoclusters in (In0.85Fe0.15−xMgx)2O3 (x = 0.00, 0.01, 0.03, 0.05) powders, was developed. The resulting powders were characterised by X-ray diffraction (XRD), superconducting quantum interference device, Mössbauer spectroscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. The XRD analysis revealed that Fe and Mg ions were incorporated into the In3+ sites in the In2O3 lattice without altering the cubic bixbyite structure. Magnetic measurements indicated the coexistence of ferromagnetic and paramagnetic phases. Room-temperature ferromagnetic behaviour with remarkable enhancement of the saturation magnetisation was observed for decreasing Fe ions and increasing nonmagnetic Mg concentrations. Mössbauer spectra confirmed the coexistence of ferromagnetic (sextet) and paramagnetic (doublet) phases, with a clear effect of Mg concentration. The enhancement in the magnetic moment with increasing Mg doping is attributed to the large defects and oxygen vacancies induced in In2O3 by Fe and Mg co-doping. These results will be useful for the development of Fe-doped In2O3 semiconductor materials for advanced applications.

    更新日期:2020-01-09
  • Swarming of micron-sized hematite cubes in a rotating magnetic field - Experiments
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    Oksana Petrichenko; Guntars Kitenbergs; Martins Brics; Emmanuelle Dubois; Régine Perzynski; Andrejs Cēbers

    Energy input by under-field rotation of particles drives the systems to emergent non-equilibrium states. Here we investigate the suspension of rotating magnetic cubes. Micron-sized hematite cubes are synthesized and observed microscopically. When exposed to a rotating magnetic field, they form rotating swarms that interact with each other like liquid droplets. We describe the swarming behaviour and its limits and characterize the swarm size and angular velocity dependence on the magnetic field strength and frequency. A quantitative agreement with a theoretical model is found for the angular velocity of swarms as a function of the field frequency.

    更新日期:2020-01-08
  • Electric and magnetic properties of some magnetodielectric composites at microwave frequency
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    Xi Yao; Yang Yang; Xiao-Li Zhang; Qian Liu; Jian-Ping Zhou; Xiao-Ming Chen; Guang-Bing Zhang

    Ni0.4Zn0.6Fe2O4/Pb(Zr0.53Ti0.47)O3 (NZFO/PZT), BaFe12O19/Pb(Zr0.53Ti0.47)O3 (BaM/PZT) and BaFe12O19/Ba0.6Sr0.4TiO3 (BaM/BST) composite ceramics were fabricated by a conventional sintering method. Their magnetic and electrical properties are compared in detail at microwave frequency, including the effect of magnetic field and polarization. In the high frequency of 2∼10 GHz, the permeability and permittivity of BaM/PZT and BaM/BST composites enjoy good stability under DC magnetic field. The permeability of NZFO/PZT composites shows a loss peak due to the domain wall resonance under magnetic field, which moves to high frequency with the increase in magnetic field. For polarized BaM/PZT and NZFO/PZT composites, the loss peak of permeability shifts to low frequency and the loss peak of permittivity becomes broadened. These clearly indicate the coupling between magnetic and ferroelectric phases at microwave frequency. The results are helpful for material selection in the design of microwave devices.

    更新日期:2020-01-08
  • Near room temperature spin reorientation and temperature evolution of magnetic structure in Mn substituted HoFeO3
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    Karthika Chandran; Pulkit Prakash; P. Neenu Lekshmi; Amitabh Das; P.N. Santhosh

    Magnetic structure and spin reorientation transition of 45% Mn substituted HoFeO3 have been investigated using bulk magnetization, neutron powder diffraction and specific heat capacity techniques. These studies confirm the presence of antiferromagnetic ordering of Fe/Mn sublattice below 336 K. The spin reorientation (SR) transition (TSR∼290 K) where the magnetic structure changes from Γ4(Ax, Fy, Gz) to Γ1(Gx, Cy, Az) is confirmed by Rietveld analysis of neutron diffraction patterns taken at various temperatures. Though the spin reorientation (SR) transition is happening at 290 K, the system is found to be in mixed Γ4(Ax, Fy, Gz) + Γ1(Gx, Cy, Az) phase from room temperature to 275 K. Below 275 K, the sample exhibits a pure Γ1(Gx, Cy, Az) structure in which the weak ferromagnetic component is absent. Bulk magnetization and specific heat capacity measurements also confirm the Néel temperature and spin reorientation transitions and support the neutron diffraction analysis.

    更新日期:2020-01-08
  • Magnetic domain structures of Sr3Co2Z hexaferrite by TEM
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-08
    William Salazar; Luis Carlos Moreno; John William Sandino

    The magnetic domain structure of Sr3Co2Z hexaferrite related to crystal orientation is investigated by Lorentz microscopy and electron holography. The sample of Sr3Co2Z, prepared by citrate method, was milled in two different crystallographic orientations by focused ion beam. One of them was prepared with its c crystallographic axis direction parallel to the electron beam at the TEM, and the other one, perpendicular to this direction. In both specimens, Lorentz micrographs revealed some structure domain walls e.g. stripes and magnetic flux-closure. Furthermore, phase micrographs acquired by electron holography revealed magnetic domain structures with 145.3°±5.2° domain walls.

    更新日期:2020-01-08
  • Magnetoelectric coupling caused by strain mediation in hetero-structured spinel-perovskite multiferroic composites
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-07
    Zohaib Manzoor; Ayesha Khalid; Ghulam M. Mustafa; Shahid M. Ramay; Shahzad Naseem; Shahid Atiq
    更新日期:2020-01-07
  • Investigation of the magnetic flux density dispersion Bd on the gaps of the FeSiBNbCu magnetically soft nanocrystalline block core
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-07
    A. Kolano-Burian; R. Kolano; P. Zackiewicz; M. Hreczka; M. Kowalczyk; M. Łukiewski; P. Łukasiak

    This paper focuses on the phenomenon of the magnetic flux density dispersion Bd on the gaps of the Fe73.5Cu1Nb3Si13.5B9 multi-gap nanocrystalline block core. Present state-of-the-art shows, that there is no comprehensive knowledge about the value of the magnetic flux density dispersion Bd on the gaps of nanocrystalline block core and the possibilities of its minimisation. The magnetic flux density dispersion Bd is the source of local eddy currents, which are the cause of increase of power loss and temperature in the chokes’ core. To discuss the effect of gap width and the method of its filling on the power losses in the core, the comparison between inserts of Teflon and magnetic mat composed of 70% Fe53.9Co29.1B13Nb1Si2Cu1 powder with a fraction of 20 – 36 µm and 30% Ultimeg epoxy resin 2004L was performed.

    更新日期:2020-01-07
  • Evaluation of local magnetic degradation by interlocking electrical steel sheets for an effective modelling of electrical machines
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-07
    S. Imamori; S. Aihara; H. Shimoji; A. Kutsukake; K. Hameyer

    Interlocking electrical steel sheets degrades magnetic characteristics of laminated cores. In this paper, local magnetic characteristics of laminated cores with interlocking have been measured. The size of the damaged region has been determined according to the measurement results in order to calculate the average magnetic characteristics of the region, which have been applied to the simulation of an electrical machine with interlocking. The results demonstrate that it is important to consider the influence of interlocking for accurate calculations of motor characteristics.

    更新日期:2020-01-07
  • A general nonlinear magneto-elastic coupled constitutive model for soft ferromagnetic materials
    J. Magn. Magn. Mater. (IF 2.683) Pub Date : 2020-01-07
    Sok Kim; Kumchol Yun; Kwanghun Kim; CholJin Won; Kyongsu Ji

    In this study, a new general nonlinear magneto-elastic coupled constitutive model was proposed for soft ferromagnetic materials under magnetic field and pre-stress. The model is based on thermodynamic theory of magnetic materials and Jiles theory on magnetomechanical effect, considering demagnetization field. This model can accurately predict the changes of magnetostrictive strain and magnetization under pre-stress; in particular, it can obviously predict the nonlinear change of magnetostrictive strain according to compressive pre-stress. In addition, this model is concise by not including the inverse function of magnetization relationship and the piecewise function of stress in its mathematical form and can be degenerated to the previous general constitutive model for giant magnetostrictive materials. The prediction result by this model is well-consistent with experimental data. In comparison with the existing constitutive models for soft ferromagnetic materials, this model was demonstrated to have obviously-improved prediction accuracy, particularly in the compressive state. In conclusion, the proposed model can fully describe the effect of pre-stress on magentostrictive strain and magnetization and the effects of magnetic field and pre-stress on Young’s modulus and relative magnetic permeability, reflecting the effect of demagnetization field on magnetomechanical characteristics.

    更新日期:2020-01-07
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