Temperature dependent structural, magnetic and microwave properties of hexagonal BaFe12O19/Ba2Co2Fe12O22 composite

In this study, the effect of different annealing temperatures (1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C) on structural, magnetic, and microwave properties of BaFe12O19(BaM)/Ba2Co2Fe12O22(Co2Y) hexaferrite composites have been investigated. XRD patterns confirmed the co-existence of M-type and Y-type phases without any secondary phase until 1050 °C temperature. With a further increase in temperature to 1100 °C, along with M and Y phases, a secondary Z-type phase starts appearing. Magnetic studies revealed that the composite exhibits a stepped M-H loop till 1100 °C, referring to a non-exchange coupled system. Notably, at 1150 °C and 1200 °C, a smooth demagnetization curve has been observed, indicating coherent rotation of M and Y magnetic spins, suggesting that both phases are coupled. The saturation magnetization (Ms) increased from 48.6 emu/g to 56.8 emu/g with a drastic decrease in coercivity (Hc). The observed variations in Ms and Hc indicated that annealing temperature strongly influences exchange coupling. Microwave studies in the Ku–band indicated that the exchange coupling significantly influences the microwave absorption losses, which can be suitably tuned with annealing temperature for various microwave device applications.