Novel in-situ core shell structured Fe-ferrite soft magnetic composite powder processed by controlled oxidation

The present work focuses on a novel approach of forming core–shell soft composite powder of Fe-Fe₃O₄ having ferrite as an electrically insulating layer around Fe-powder. The approach involves simple low-temperature in-situ oxidation-diffusion to obviate the interface delamination of core–shell structure while enabling % phase-control of ferromagnetic-core and ferrimagnetic-shell with time–temperature variation. Fe-powder was heated upto 400 °C-600 °C and subjected to oxidation for 5–15 min before cooling under inert atmosphere (N₂). A thorough investigation of core–shell powders was done using Micro-XRD, FE-SEM, EBSD and Saturation magnetization (Ms) was measured using PPMS. The shell thickness increased with increasing temperature and oxidation time. Co-relation between phase percentages in the core–shell powder & Ms values were established. The process resulted in higher Ms values (209–136 emu/g) compared to those reported in the literature in such powders with average shell thickness ranging from 0.4 µm to 14.3 µm, retaining the characteristic soft magnetic property of Fe-Fe₃O₄ composite powder.