Magnetic, elastic, dielectric, microwave absorption and optical characterization of cobalt-substituted nickel spinel ferrites

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Highlights

Spinel ferrite Ni0.1Co0.9Fe2O4: an appropriate material for various applications such as

  • High density recording media (optimized combination of MS and Hc).

  • Fabrication of electronic components (high ε').

  • Microwave absorbers (RL = −44.48 dB at f = 15.74 & t = 6 mm).

  • Optical equipments (high photo-luminous intensity).

Abstract

Magnetic, elastic, dielectric, microwave absorption and optical properties of nickel cobalt ferrites Ni1-xCoxFe2O4(x=0.0,0.15,0.30,0.45,0.60,0.75,0.90,1.0) synthesized using Pechini’s sol–gel method are investigated. Saturation magnetization, coercivity and Curie temperature increased with doping of cobalt. An optimized combination of high MS (86.12 emu g−1) and lower coercivity (694.7 Oe) was obtained for composition NC 0.90. Curie temperature increased from 602 °C to 705 °C as amount of Co increased from 0.0 to 1.0. In FT-IR spectrum, characteristic absorption bands were observed in 400–600 cm−1 range. Impedance analyzer was used to determine dielectric and impedance properties in 20 Hz–120 MHz frequency range. The prepared ferrites were evaluated for their applications in 12.4–18 GHz frequency band using vector network analyzer (VNA). Minimum reflection loss of −44.48 dB at 15.74 GHz frequency was obtained for composition NC 0.90. Optical spectra at excitation wavelength of 350 nm show sharp peaks around 330 nm in all the compositions.

Introduction

Recently, considerable attention has been given to the nano-sized spinel ferrites due to their versatile fundamental and technical applications. These ferrites have a broad spectrum of applications including microwave absorbers [1], electronic and communication devices [2], magnetic recording media, biotechnology [3], computer memories [4], gas sensors, ferro-fluids, catalysts [5], magnetic drug carrier, waste water processing [6], solid oxide fuel cells [7] to cite a few. Spinel ferrites can be depicted by the chemical formula MO.Fe2O3, where M refers to divalent metal ions. These ferrites possess face-centered cubic crystal structure with metal cations occupying interstitial positions. Properties of these ferrites are governed by the synthesis method and site occupancy by different metal ions. Synthesis method plays a vital role in deciding the purity of phase and size of the particles. Literature reports a significant variation in the structural and magnetic properties as size of particle reduces from micrometer to nanometer range [8]. Occupancy of cationic sites by different metal ions decides the magnetic, dielectric, optical and other properties.

In the midest of different spinel ferrites, nickel–cobalt ferrites have a festive significance due to their magneto-resistive properties. Researchers have made many efforts to optimize their properties by adopting different synthesis methods [5], [6], [7], [8], [9], [10], [11], [12] or substituting different ions [13], [14], [15], [16], [17], [18]. Rodrigues et al. (2015) investigated the structural and magnetic properties of Ni-Co ferrites prepared using combustion reaction assisted with microwaves [11]. Hcini et al. (2017) presented the dielectric and complex impedance properties of Ni0.6Co0.4Fe2O4 prepared by Pechini sol–gel method in frequency range 40 Hz–10 MHz [12]. K. Vijay Babu and his co-workers reported structural and dielectric properties of pure nickel ferrite along with ESR analysis [19]. Ni-Co ferrite series prepared using sol–gel method and glycine fuel was reported by Jithin and his team [20]. But there is no cumulative reporting on Ni-Co spinel ferrites which presents all these properties, to the best of authors’ knowledge.

The aim of this communication is to present and discuss proper correlation of magnetic, elastic, dielectric (20 Hz-120 MHz frequency), microwave Ku-band (12.4–18 GHz) and optical properties of nickel cobalt mixed ferrites at the same platform. The spinel ferrite compositions were prepared using Pechini’s sol–gel auto-combustion method [21]. To the best of our knowledge for the first time, elastic, Ku microwave electromagnetic and optical properties of these compositions are being reported. On the basis of analysis done, the prepared materials are proposed for practical applications in recording media, electric devices, microwave absorbers and optical equipment fabrication.

Section snippets

Experimental section

Ni1-xCoxFe2O4 (x=0.00,0.15,0.30,0.45,0.60,0.75,0.90,1.00) spinel ferrites were synthesized using Pechini’s sol–gel method with citric acid as fuel. Ethylene glycol and hydrogen peroxide were used as polymerizing and reducing agents respectively. Final sintering of the powder was done at 1000 °C for 6 h to ensure proper grain formation. Complete synthesis process, structural characterization and X-band electromagnetic properties of these compositions have been previously reported elsewhere [21].

Magnetic properties using VSM and ESR analysis

Room temperature hysteresis loops of Ni-Co spinel ferrites, obtained in ± 20 kOe field range, are depicted in Fig. 1. Normal S-shaped curves are observed for all compositions which show their ferrimagnetic character [3]. Inset (Fig. 1) shows the increase in height of the curve with increase in cobalt substitution, which depicts an increase in saturation magnetization MS. The values of saturation magnetization (Table 1) are calculated by two methods: experimentally and theoretically. The

Conclusions

Spinel ferrites with chemical composition Ni1-xCoxFe2O4, prepared by Pechini’s sol gel method are investigated thoroughly for their magnetic, elastic, dielectric, microwave absorption and optical properties. Saturation magnetization, magnetic moment and Curie temperature are observed to increase with the doping amount. An optimized combination of high saturation magnetization (86.12 emu g−1) and lower coercivity (694.7 Oe) is achieved in composition NC 0.90, which suggests its possible use in

Data availability

The raw/ processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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