Speaker
Description
Soft magnetic composites (SMCs), which have isotropic ferromagnetic behavior, high saturation magnetization, high permeability, and relatively low core loss, have been regarded as key components of electromagnetic systems in higher frequency range [1]. This work focuses on investigating the effect of adding Al$_2$O$_3$ or h-BN as a layer keeping the electric insulation of the NiFe-based SMC structure. Soft magnetic composites based on NiFeMo powder particles encapsulated in Al$_2$O$_3$ or h-BN matrix are prepared by powder metallurgy process followed by compaction. The structure and various magnetic properties related to their soft magnetic performance are analyzed. Four samples prepared are with volume ratio ($98.8:1.2$ and $95:5$) of the mixture of NiFeMo and Al$_2$O$_3$ or h-BN.
The most important properties studied here are complex permeability and total energy loss. Further important characteristics are initial relative permeability, maximum relative permeability and coercivity. As both the electroinsulators contribute to the entire electrical resistivity, the resulting composites possess improved electromagnetic performance. This is fulfilled by electrically insulating coating on the surface of powder particles, limiting the eddy current paths into the cross-section of isolated particles. The magnetic losses in the frequency range from DC to $50$ kHz on ring-shaped samples are shown to be suppressed thanks to the lower eddy currents. The real part of complex permeability keeps a constant value until higher frequencies in comparison with NiFeMo sample. The peak of imaginary part of relative complex permeability is shifted from $5$ kHz for NiFeMo to $10.5$ kHz for the sample with $1.2\%$ and to $80$ kHz for the sample with $5\%$ Al$_2$O$_3$ content. Position of peaks for samples with h-BN are at significantly higher values, $250$ kHz for sample with $1.2\%$ and 400 kHz for sample with $5\%$ h-BN content. Herein, the imaginary components shift with rising electric insulation amounts, corresponding with the measured electrical resistivity values. Therefore, the use of the h-BN as an insulating layer with more uniform distribution in soft magnetic composites has promising potential in meeting requirements in the high-frequency range.
Acknowledgements
This work has been supported by the Scientific Grant Agency of the Ministry of Education, Science, Research & Sport of the Slovak Republic and the Slovak Academy of Sciences (VEGA 1/0132/24, and VEGA 1/0403/23) and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.
References
[1] E. A. Périgo et al., “Past, present, and future of soft magnetic composites,” Applied Physics Reviews, vol. 5, no. 3. AIP Publishing, p. 031301, Sep. 2018. https://doi.org/10.1063/1.5027045
