Research articlesSuppressed domain wall damping in planar BaM hexaferrites for miniaturization of microwave devices
Introduction
Antenna substrate materials, made of low-loss magnetic materials, ideally have high permeability at applied frequencies to decrease antenna size without degradation to performance. With increasing demands from telecommunication devices and systems, the resonance frequency of ferrites must be shifted well above 5 GHz with high permeability and low losses [1].
Limited by the Snoek’s relationship, attaining high permeability in ferrites has been a longstanding challenge for high frequency applications. It is difficult for spinel ferrites to possess high permeability in the gigahertz range due to low anisotropy fields and low resonance frequencies.
Hexagonal ferrites have attracted more attention for gigahertz application because planar anisotropy of hexagonal ferrites extends Snoek’s limit [2], which is useful to shift the resonance frequency beyond GHz. Many methods used to adjust the planar anisotropy field or improve sintering process to lower the damping coefficient have been reported for BaM [3], [4], [5], Co2Y [6], [7] and Co2Z [8], [9], [10] ferrites to increase the permeability and decrease magnetic loss. However, the permeability is usually lower than 2.5 when the working frequency is above 1 GHz. It is difficult to meet the requirement of matching impedance. In general, there are two resonance frequencies observed in the permeability spectrum with frequency: one is domain wall motion at low frequency; while the other is resonance at high frequency stemming from spin rotation. It is clear that the domain wall resonance may limit lower operating frequencies for antenna operations. One of the solutions to this limiting magnetic loss is to have polycrystalline ferrites with finer grains, which enables the reduction of domain wall losses to the total loss. The other solution is to make polymer-based composites by mixing ferrites, or magnetic alloy particles, within dielectric polymer hosts [11], [12], [13]. However, the composite path leads to a marked reduction in permeability. A number of published works have revealed that it remains difficult to realize a permeability above 3 while retaining a magnetic loss tangent of <0.1 over a frequency range of 1–5 GHz.
Here, we present a path to realizing both high permeability and low loss by means of the introduction of Bi2O3 to CoRu-doped BaM type ferrites. The addition of Bi2O3 effectively tailors the microstructure of polycrystalline ferrites thus modifying the role of domain wall resonance to both permeability and magnetic loss. The experimental results indicate that the ferrite materials have a permeability of ~3 at a frequency >1 GHz with a magnetic loss tangent of ~0.05 and 0.1 at 1 GHz and 1.5 GHz, respectively. The results demonstrate great potential for application as substrates for miniaturized antenna at f 1 GHz.
Section snippets
Experimental
The BaCo1.2Ru0.2Fe10.9O19 M-type hexaferrite were prepared via the conventional solid-state reaction method. Starting materials of BaCO3, Co3O4, RuO2 and Fe2O3 of reagent grade purity were mixed, dried and calcined at 1100 °C for 4 h. The calcined powders were then ground by a planetary ball mill. During ball milling, one of the calcined powders was milled without any additive as a control sample (i.e., Sample A), whereas the other was milled with 1 wt-% Bi2O3 (i.e., Sample B). After
Results and discussion
Fig. 1 presents permeability and magnetic loss values at 1 GHz for Samples A and B sintered at different temperatures. The permeability of Sample A, sintered in air, increases slightly with sintering temperature, but the magnetic loss exhibits different behavior and experiences a minimum at a sintering temperature of 1260 °C. To further lower magnetic losses, the sample was sintered in an oxygen gas atmosphere while an additive (Bi2O3) is incorporated. Fig. 1(b) indicates that the additive
Conclusion
We have demonstrated that Ru substituted BaM-type hexaferrite has excellent high frequency magnetic characteristics, but the magnetic loss properties induced by domain wall motion remains a hindrance to practical applications. Our attempt to lower magnetic losses by tailoring grain morphology, magnetic domain structure and cut-off frequency by the introduction of Bi2O3 additive in conjunction with co-doping of Co and Ru ions in the BaM ferrite led to marked success. Experimental data revealed a
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.
CRediT authorship contribution statement
Qifan Li: Conceptualization, Methodology, Formal analysis, Writing - original draft. Yajie Chen: Resources, Writing - review & editing. Qifan Li: Formal analysis, Validation. Lezhong Li: Data curation, Investigation. Kun Qian: Formal analysis, Investigation. Vincent G. Harris: Supervision, Writing - review & editing.
Acknowledgement
This research is funded by Rogers Corporation.
References (24)
- et al.
Low-loss Z-type hexaferrite (Ba3Co2Fe24O41) for GHz antenna applications
J. Magn. Magn. Mater.
(2016) - et al.
BiFeO3 tailored low loss M-type hexaferrite composites having equivalent permeability and permittivity for very high frequency applications
J. Alloys Compd.
(2015) - et al.
Phase formation, sintering behavior and magnetic property of Bi-Co-Ti substituted M-type barium hexaferrite
J. Alloys Compd.
(2013) - et al.
Study of the dielectric and magnetic properties of Co2Y, Y-type hexaferrite (Ba2Co2Fe12O22) added with PbO and Bi2O3 in the RF frequency range
J. Alloys Compd.
(2010) - et al.
Aluminum substituted low loss Z-type hexaferrites for antenna applications
Phys. B Condens. Matter.
(2013) - et al.
Particle-size distribution modified effective medium theory and validation by magneto-dielectric Co-Ti substituted BaM ferrite composites
J. Magn. Magn. Mater.
(2018) - et al.
Layered dielectric-magnetic composite structures for Rf-applications
Compos. Struct.
(2010) - et al.
Influence of V2O5 addition on the grain growth and magnetic properties of Mn-Zn high permeability ferrites
J. Magn. Magn. Mater.
(2007) Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics
Prog. Mater. Sci.
(2012)- et al.
Low loss Z-type Ba3Co2Fe24O41 hexaferrites for antennas and RF devices
IEEE Trans. Magn.
(2011)