Synthesis of low-temperature sintered M-type barium ferrites with enhanced microstructure, magnetic and dielectric properties

M-type barium ferrites (BaM) are utilized in the preparation of ferrite circulators due to their excellent magnetic properties. However, high sintering temperature of BaM is one of the major problems unsuitable for actual production requirements. In this study, Bi ³⁺ ions from the low-melting point oxide bismuth(III) oxide (Bi ₂O ₃) were made to substitute Fe ³⁺ ions to reduce the sintering temperature and control the magnetic properties. Addition of an appropriate content of Bi ³⁺ ions at the sintering temperature of 900 °C led to the disappearance of the second phase, and a pure BaBi _x(CoTi) _1.2Fe _9.6−xO ₁₉ phase was formed. The results exhibited the existence of dense microstructure in BaM ceramics. Moreover, when the x value of Bi ₂O ₃ was 0.45, the permeability of the sample increased from 12.59 to 21.6 at 10 MHz, the saturation magnetization reached 3313.34 gauss, and the permittivity increased from 10.75 to 21.24. Permeability and permittivity were found to be approximately equal. Interestingly, addition of excessive Bi ₂O ₃ led to the formation of the second phase, and the microstructure exhibited the appearance of abnormal grains. However, BaM still maintained acceptable magnetic properties. The results showed that the addition of Bi ³⁺ ions could reduce the sintering temperature of the ferrite and simultaneously adjust the magnetic and dielectric properties. Therefore, this material may have good performance in the preparation of ferrite circulators.