Thermal instability of Co-substituted barium hexaferrites with U-type structure

Thermal stability studies of Co-substituted barium hexaferrites with the U-type structure are reported. Samples were prepared using solid-state reaction and high-energy milling at 1300 and 1250 °C, respectively. The influence of different annealing conditions on their compositions and magnetic properties was studied. Thermal instability of the studied compounds was observed at as low as 600 °C. Through x-ray powder diffraction, chemical analysis, and thermomagnetic measurements it was confirmed that a degradation of the U-hexaferrites occurred during the annealing at 600–800 °C. The observed changes in the samples’ phase compositions and structures did not have a significant influence on their magnetization and microwave properties.