Influence of manganese substitution and annealing temperature on the formation, microstructure and magnetic properties of Mn–Zn ferrites

The effects of annealing temperature and manganese substitution on the formation, microstructure and magnetic properties of MnxZn1−xFe2O4 (with x varying from 0.3 to 0.9) through a solid-state method have been investigated. The correlation of the microstructure and the grain size with the magnetic properties of Mn–Zn ferrite powders was also reported. X-ray diffraction (XRD), a scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM) were utilized in order to study the effect of variation of manganese substitution and its impact on crystal structure, crystalline size, microstructure and magnetic properties of the ferrite powders formed. The XRD analysis showed that pure single phases of Mn–Zn ferrites were obtained by increasing the annealing temperature to 1200–1300 °C. Increasing the annealing temperature to ⩾1300 °C led to abnormal grain growth with inter-granular pores and this led to a decrease in the saturation magnetization. Moreover, an increase in the Mn2+ ion substitution up to x=0.8 increased the lattice parameter of the formed powders due to the high ionic radii of the Mn2+ ion. Mn–Zn ferrites phases were formed and the positions of peaks were shifted by substituting manganese. The average crystalline size was increased by increasing the annealing temperature and decreased by increasing the substitution by manganese up to 0.8. The average crystalline size was in the range 95–137.3 nm. The saturation magnetization of the Mn–Zn-substituted ferrite powders increased continuously with an increase in the Mn concentration up to 0.8 at annealing temperatures of 1200–1300 °C. Further increase of Mn substitution up to 0.9 led to a decrease of saturation magnetization. The saturation magnetization increased from 17.3 emu/g for the Mn0.3Zn0.7Fe2O4 phase particles produced to 59.08 emu/g for Mn0.8Mn0.2Fe2O4 particles.