Core loss reduction in Fe-6.5Â wt.%Si/SiO2 core-shell composites by ball milling coating and spark plasma sintering

The Fe-6.5 wt.%Si/SiO2 core-shell composite powders and compacts have been prepared by simple ball milling coating and spark plasma sintering process. The microstructure, magnetic and electrical properties of the compact samples obtained at different sintering temperatures were investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, vibrating sample magnetometer, and impedance analyzer. The relative densities of Fe-6.5 wt.%Si/SiO2 composite compacts first increase with sintering temperature from 800 °C to 1150 °C, and then keep nearly unchanged with higher temperature, while the coercivity and electrical resistivity change in the opposite direction. The saturation magnetization fluctuates around an identical value with increasing the sintering temperature from 800 °C to 1250 °C. The Fe-6.5 wt.%Si/SiO2 composite compact sintered at 1150 °C displays excellent soft magnetic properties: saturation magnetization of 153.9 emu/g, coercivity of 14 Oe, relative permeability of 8.6 × 103 at 50 Hz, respectively. The Fe-6.5 wt.%Si/SiO2 core-shell composite compacts clearly exhibit much higher electrical resistivity and lower core loss (1.4 × 10−5 Ω m and 18.1 W/kg (P5/400)) than those of Fe-6.5 wt.%Si compacts without core-shell structures (9.6 × 10−7 Ω m and 37.9 W/kg (P5/400)). The core-shell structures introduced here is a good potential method to increase electrical resistivity and reduce core loss of soft magnetic materials, which can obviously improve energy conversion efficiency of electric-magnetic switching device.