VP18-06 Temperature dependent structural, magnetic and microwave properties of hexagonal BaFe12O19/Ba2Co2Fe12O22 composite
Creators: Sonal Singh
Puneet Sharma
Pawandeep Kaur
Bhupendra Chudasama
Publisher: name: IEEE
Year: 2025

In recent past, exchange coupled composites of hard and soft ferrites have gained attention for their applications in microwave absorbers. Among the choices for the hard ferrites, M-type hexaferrites are prominent for their c-axis anisotropy, high magnetocrystalline anisotropy (Ha ~17 kOe) and high ferromagnetic resonance (FMR) frequency (~36 GHz). Extensive work has been reported on composites with M-type hexaferrite as the hard phase and cubic spinel/garnet ferrites as the soft phase. However, composites with a hexagonal soft magnetic phase are still unexplored. Y-type hexaferrites,which exhibit c-plane anisotropy and FMR frequencies up to 14 GHz, have distinct magnetic properties from M-type ferrites. As evident, one type of hexaferrite has limited frequency range, therefore focus has been shifted on development of composite ferrites with contrast magnetic and microwave properties. In the present work, composite of BaFe12O19 (BaM)/Ba2Co2Fe12O22 (Co2Y) in 70/30 weight ratio were prepared by one-pot method. Effect of different annealing temperatures (1000 °C-1200 °C) on structural, magnetic and microwave properties have been investigated. XRD patterns confirmed the co-existence of M-type and Y-type phases without any secondary phase till 1050 °C temperature (Fig.1). With further increase in temperature to 1100 °C, along with M and Y phases secondary Z-type phase start appearing. Magnetic studies revealed that composite exhibit stepped M-H loop till 1100 °C, referring to non-exchange coupled system (Fig.2). Notably, at 1150 °C and 1200 °C smooth demagnetization curve has been observed, indicating coherent rotation of M and Y magnetic spins suggesting that phases are coupled. Saturation magnetization (Ms) increased from 48.6 emu/g to 56.88 emu/g with drastic decrease in coercivity (Hc). The observed variations in Ms and Hc indicated that annealing temperature has strong influence on exchange coupling. Microwave studies in Ku–band indicated that the exchange coupling significantly influences the microwave absorption losses which can be suitably tuned with annealing temperature.
In recent past, exchange coupled composites of hard and soft ferrites have gained attention for their applications in microwave absorbers. Among the choices for the hard ferrites, M-type hexaferrites are prominent for their c-axis anisotropy, high magnetocrystalline anisotropy (Ha ~17 kOe) and high ferromagnetic resonance (FMR) frequency (~36 GHz). Extensive work has been reported on composites with M-type hexaferrite as the hard phase and cubic spinel/garnet ferrites as the soft phase. However, composites with a hexagonal soft magnetic phase are still unexplored. Y-type hexaferrites,which exhibit c-plane anisotropy and FMR frequencies up to 14 GHz, have distinct magnetic properties from M-type ferrites. As evident, one type of hexaferrite has limited frequency range, therefore focus has been shifted on development of composite ferrites with contrast magnetic and microwave properties. In the present work, composite of BaFe12O19 (BaM)/Ba2Co2Fe12O22 (Co2Y) in 70/30 weight ratio were prepared by one-pot method. Effect of different annealing temperatures (1000 °C-1200 °C) on structural, magnetic and microwave properties have been investigated. XRD patterns confirmed the co-existence of M-type and Y-type phases without any secondary phase till 1050 °C temperature (Fig.1). With further increase in temperature to 1100 °C, along with M and Y phases secondary Z-type phase start appearing. Magnetic studies revealed that composite exhibit stepped M-H loop till 1100 °C, referring to non-exchange coupled system (Fig.2). Notably, at 1150 °C and 1200 °C smooth demagnetization curve has been observed, indicating coherent rotation of M and Y magnetic spins suggesting that phases are coupled. Saturation magnetization (Ms) increased from 48.6 emu/g to 56.88 emu/g with drastic decrease in coercivity (Hc). The observed variations in Ms and Hc indicated that annealing temperature has strong influence on exchange coupling. Microwave studies in Ku–band indicated that the exchange coupling significantly influences the microwave absorption losses which can be suitably tuned with annealing temperature.