Pseudo Core-Shell Permalloy (Supermalloy)@ZnFe2O4 Powders and Spark Plasma Sintered Compacts Based on Mechanically Alloyed Powders

Soft magnetic composites cores were produced by Spark Plasma Sintering (SPS) from Ni3Fe@ZnFe2O4 and NiFeMo@ZnFe2O4 pseudo-core-shell powders. In the Fe-Ni alloys@ZnFe2O4 pseudo-core-shell composite powders, the core is a large nanocrystalline Permalloy or Supermalloy particle obtained by mechanical alloying, and the shell is a pseudo continuously layer of Zn ferrite particles. The pseudo-core-shell powders have been compacted by SPS at temperatures between 500-700 ºC, with a holding time of 0 minutes. Several techniques were used for the characterisation of the powders and sintered compacts: X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, magnetic hysteresis measurements (DC and AC) and electrical resistivity. The electrical resistivity is stabilised at values of about 7·10-3 Ω·m for sintering temperatures between 600-700 °C and this value is 3 orders of magnitude higher than the electrical resistivity of sintered Fe compacts. The best relative initial permeability was obtained for the Supermalloy/ZnFe2O4 composite compacts sintered at 600 ºC, which decreases linearly for the entire frequency range studied, from around 95 to 50. Up a frequency of 2,000 Hz the power losses are lower than 1.5 W/kg. At the frequency of 10 kHz, the power losses are larger, but they remain at a low level. In the case of Supermalloy/ZnFe2O4 composite compact SPS-ed at 700 °C, the specific power losses are even lower than 5 W/kg. The power losses decomposition proved that intra-particles losses give the main part of the losses.