The Dependence of Magnetic and Mechanical Properties on Composition and Processing in Air Fired MnZn Ferrites

Abstract
The relationship between magnetic and mechanical properties has been studied as a function of composition, atmosphere and temperature for a series of MnZn ferrites. When processed in air, strength and permeability are critically dependent upon the formation of Mn²⁺ and Fe²⁺ on sintering, and residual stresses introduced via subsequent (re)oxidation upon cooling. In Fe deficient ferrites, properties are determined by the reoxidation of Mn²⁺, which introduces residual tensile stresses on cooling, so that low strength/high µ_i are observed. In the Fe excess region, reoxidation of Fe²⁺ on cooling introduces compressive stresses, resulting in high strength/low µ_i. Both strength and permeability increase with increasing sintering temperature in Fe excess materials. Cooling in N₂ prevents reoxidation, and results in increased permeability for Fe excess ferrites.