Influence of Microstructure on the DC-Bias-Superposition Characteristics of NiZn Ferrites

The influence of microstructure on the magnetic properties, especially the dc-bias-superposition characteristics, of NiZn ferrites has been investigated. The value of saturation magnetic flux density (B_s) first increased and then changed little with variation of the sintered density, and showed little relation to the microstructure. Coercivity (H_c) decreased continuously with increasing average grain size. ΔB (B_s-remanence) first increased with increasing average grain size, but then gradually decreased when abnormal grain growth prevailed. The incremental permeability (permeability with magnetic field superposition) was influenced by both ΔB and H_c. A sample with higher ΔB and H_c favored the attainment of a higher incremental permeability. The Q-factor was mainly determined by the sintered density and microstructure. To sum up, a uniform and dense microstructure with relatively small average grain size is favorable for obtaining better dc-bias-superposition characteristics, including permeability and Q-factor.