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

TL;DR

Researchers created magnetic composite materials using a special sintering method and found they have low power losses and high resistivity, making them suitable for magnetic applications.

Contribution

The paper introduces a novel pseudo-core-shell composite material with enhanced magnetic and electrical properties through spark plasma sintering.

Findings

The composite materials achieved an electrical resistivity of about 7 × 10−3 Ω·m, three orders of magnitude higher than sintered Fe.

Supermalloy/ZnFe2O4 compacts sintered at 600 °C showed the best initial permeability, decreasing linearly with frequency.

Power losses in the composite materials remained low, with specific losses below 5 W/kg at higher sintering temperatures.

Abstract

Soft magnetic composite 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 continuous layer of Zn ferrite particles. The pseudo-core-shell powders have been compacted by SPS at temperatures between 500–700 °C, with a holding time of 0 min. 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 three 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 °C, which decreases linearly for the entire frequency range studied, from around 95 to 50. At a frequency of 2000 Hz, the power losses are smaller than 1.5 W/kg. At a frequency of 10 kHz, the power losses are larger, but they remain at a reduced 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-particle losses are the main type of losses.

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