Microstructure and magnetic properties of the FeSiAl soft magnetic composite with a NiFe2O4-doped phosphate insulation coating

Abstract

Novel FeSiAl soft magnetic composites (SMCs) with a phosphate insulation coating doped with magnetic NiFe2O4 nanocrystalline particles were prepared. They exhibited high permeability, ultra-low loss, and high thermal stability. The saturation magnetization of the FeSiAl SMC increased, while the coercivity decreased due to the exchange coupling of the magnetic nanocrystalline particles. The total loss of the novel SMC decreased to 139.93 kW/m3 at 100 mT and 100 kHz, which is only one-third of that of common commercially available Sendust composites, while the permeability was up to 62 for the reduced demagnetization field. Furthermore, three-dimensional loss separation was performed based on the nonlinear regression method, and the complex permeability was separately addressed as the domain-wall movement and spin resonance parts. The minimum total loss was ascribed to the significantly reduced hysteresis loss and the slightly reduced eddy current loss, corresponding to the low coercivity (Hc = 0.341 Oe) and high impedance (|Z| = 67.1 MΩ). This was attributed to the improved magnetic properties and resistance of the insulation coating, which was related to the magnetic nanoparticles embedded in the insulation coating. The permeability was mainly derived from the spin resonance due to the complete insulation coating and ultrafine particles. This novel SMC with a phosphate insulation coating doped with magnetic NiFe2O4 nanocrystalline particles provides a high-efficiency, high-frequency, and high-saturation soft magnetic device for switching power supplies, photovoltaic inverter boost inductors, and other applications.