The effect of microstructure on the initial permeability of Ni-Zn ferrite

We have studied the sintering behavior, microstructure, and permeability of the ferrite Ni0.50Zn0.50Fe2O4 sintered at temperatures from 1000 degrees C to 1400 degrees C for various dwell times. The shrinkage rate is maximum at 1140 degrees C; hence samples sintered at T >= 1100 degrees C exhibit densities larger than 97%. Moderate grain growth is observed up to 1250 degrees C; however, if the density exceeds a threshold of 98% enhanced grain growth sets in. All samples are single-phase spinels with the lattice constant slightly increasing with sintering temperature. At T >= 1300 degrees C significant ZnO evaporation sets in and the corresponding change in ferrite composition is indicated by mass loss, EDX-analysis, and Seebeck coefficient measurements. The complex permeability spectra show systematic changes with sintering temperature and dwell time. For samples sintered at 1100 degrees C, the permeability increases from mu' = 133 for a dwell time of 30 min to mu' = 318 after 24 h sintering. The variation of the permeability is discussed as function of density and grain size. The non-magnetic grain boundary model is applied to interpret the grain size dependence of the permeability.

Automated summary

This study investigated the sintering behavior, microstructure, and permeability of Ni0.50Zn0.50Fe2O4 ferrite sintered at temperatures ranging from 1000 degrees C to 1400 degrees C with different dwell times. The results showed that the maximum shrinkage rate occurred at 1140 degrees C, resulting in samples sintered at temperatures greater than or equal to 1100 degrees C having densities higher than 97%. Moderate grain growth was observed up to 1250 degrees C, but enhanced grain growth occurred if the density exceeded a threshold of 98%. All samples exhibited a single-phase spinel structure with a slightly increased lattice constant with sintering temperature. At temperatures greater than or equal to 1300 degrees C, significant ZnO evaporation occurred, leading to changes in ferrite composition indicated by mass loss, EDX-analysis, and Seebeck coefficient measurements. The complex permeability spectra showed systematic changes with sintering temperature and dwell time. For samples sintered at 1100 degrees C, the permeability increased from mu' = 133 after 30 minutes of dwell time to mu' = 318 after 24 hours of sintering. The variation in permeability was discussed in relation to density and grain size, with the non-magnetic grain boundary model used to interpret the grain-size dependence of permeability.