Mn–Zn ferrites with high Fe ₂ O ₃ content obtained by the nitrate–citrate sol–gel auto‐combustion method

Abstract In this paper, powders and sintered cores of Mn–Zn ferrites with Fe 2 O 3 contents ranging from 61.8 to 76.9 mol.% were investigated. The high iron oxide powders obtained by the nitrate–citrate sol–gel auto‐combustion method contained 96 wt.% ferrite phase without additional heat treatment. After air quenching at 1300°C, the ferrite cores obtained from these powders have a two‐phase structure. Single‐phase ferrites with Fe 2 O 3 contents ranging from 61.8 to 76.9 mol.% were obtained by sintering in an atmosphere with a residual air pressure of 20 Pa at 1280°C. As the Fe 2 O 3 content increases from 61.8 to 76.9 mol.%, initial magnetic permeability decreases from 1100 to 150, coercivity ( H c ) increases from 70 to 240 A/m, but high temperature stability of maximum flux density ( B m ) is achieved—in the range of 25°C–100°C, the decrease of B m is not more than 3%. Sintering at 1300°C resulted in a decrease of initial magnetic permeability and B m values due to active evaporation of zinc.