One approach to reduce eddy current loss is to restrict the flow of eddy currents by increasing the resistivity of the material. For this purpose, insulating oxide particles (e.g., CaO, SiO2, Nb2O5, Ta2O5, HfO2, ZrO2, and V2O5) have been shown to preferentially increase the grain boundary resistance of polycrystalline ferrite cores by segregating them to grain boundary regions, which results in a decrease in eddy current loss. However, this approach comes with a substantial cost to permeability originating from the presence of the nonmagnetic impurities at the grain boundaries and the associated increased grain boundary effective thickness, which frustrates and weakens the long-range intergranular magnetic coupling.
In 2012, Chen and Harris demonstrated the efficacy of the use of 1 - 10 wt-% highly‑resistive, magnetic, insulating grain boundary phase of NiZn spinel ferrite introduced to a principal MnxZn1-xFe2O4 (MZFO) to effectively reduce losses for applications at frequencies greater than 1 MHz.
Technology Overview
Northeastern researchers have created a novel approach that has been demonstrated for simultaneous substantially reduced eddy current losses and retained long-range magnetic continuity and high permeability using insulating magnetic intergranular inclusions.
Here, ferrimagnetic yttrium iron garnet (YIG; Y3Fe5O12) and diamagnetic barium titanate (BTO, BaTiO3) nanoparticles (NPs) were introduced to the processing of semiconductor MnZn-ferrite (MZFO) of the composition (Mn0.69Zn0.20)Fe2.11O4. 
Selection of the YIG NPs as the ferrimagnetic grain boundary insulating phase was due to its high intrinsic electrical resistivity (i.e., >1010 Ohm-cm). Alternatively, BTO was chosen as the diamagnetic control additive due to its similar electrical properties (i.e., >1012 Ohm-cm). 
Additionally, both additives (i.e., YIG: garnet, space group La3d; BTO: perovskite, space group P4mm) have crystallographic structures markedly different from the MZFO (spinel, space group Fd3m) and provide incongruent grain boundary phases that act to disrupt the flow of intergranular eddy currents.
In this method, the YIG additives were found to not only substantially reduce total power loss attributable to the eddy current loss component, but also sustain a high permeability. 
- Decrease in eddy current loss 
- Highly sustained permeability and magnetization 
- Can be used as an inductor core for >100 KHz applications such as switch-mode power supplies, power converters, filters, and chokes
- License
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- Research collaboration
Patent Information:
For Information, Contact:
Mark Saulich
Associate Director of Commercialization
Northeastern University
Yajie Chen
Parisa Andalib
Vincent Harris