Defect induced ferromagnetism in h-BaTiO₃ synthesized from t-BaTiO₃ by microwave heating

Structure modification of tetragonal BaTiO₃ (t-BaTiO₃) and corresponding phase transition by microwave heating were investigated. The sample compound was heated by 1.8 kW power and 2.45 GHz frequency microwave irradiation under N₂ atmosphere in a short experimental duration of 14 min. The maximum temperature of the surface of the sample was 1115 °C. The structure of the microwave irradiated BaTiO₃ was then analyzed by employing X-ray diffraction (XRD), Rietveld refinement analysis, Raman spectroscopy, and field emission scanning electron microscopy techniques. From XRD and Rietveld refinement analysis, the microwave irradiated BaTiO₃ sample was composed of hexagonal 89%, cubic 5% and tetragonal 6%. Due to the direct internal heating mechanism of microwaves, the core temperature of the sample might be higher than the phase transition temperature. The magnetic behavior of the sample was investigated using a vibrating sample magnetometer. The results indicated that the microwave irradiated BaTiO₃ exhibited mixed magnetism: ferromagnetic nature at low applied magnetic fields and diamagnetic nature at high applied magnetic fields.