Field-Assisted Sintering of FeCo/MnZn Ferrite Core-Shell Structured Particles

Abstract

Core-shell FeCo/MnZn ferrite powders were prepared by the sol-gel method with ferrite contents ranging from 5.01 wt.% to 17.10 wt.%. The target composition for the MnZn ferrite shell was Mn_0.8Zn_0.2Fe₂O₄. The powders were compacted into bulk composites with FeCo separated by an oxide matrix using the field-assisted sintering technique (FAST) at 800°C for 10 min. All resulting compacts achieved relative density > 95%. As the MnZn ferrite content in the original core-shell powder increases from 5.01 wt.% to 17.10 wt.%, the saturation magnetization of the compacts decreases from 222 Am²/kg to 165 Am²/kg, and the coercivity increases from 772 A/m to 1654 A/m. XRD of the compacts indicates that a chemical reaction dissociates the spinel-structured MnZn ferrite into a rocksalt structured phase. Thermodynamics calculation indicates that the reaction happens between FeCo and MnZn ferrite at 800°C, but favors MnZn ferrite at temperatures ≤ 400°C. This prediction was substantiated by FAST consolidation at 400°C.