Investigation of crystal structure formation under microwave heating

Recently, we have developed new methods to form nano-structures consisting of small magnetic domains of 5–20 nm with random orientations, when some ferromagnetic materials are exposed to the magnetic field with microwave frequencies. To investigate the consequences of the non-equilibrium reactions by electromagnetic wave energy, we performed polarized neutron diffraction measurements to characterize the magnetic nano-domain structure of the microwave heated magnetite powder by using the polarized neutron triple-axis spectrometer TAS-1 at JRR-3 of Japan Atomic Energy Agency. In the magnetite samples heated under magnetic field of microwave up to 1000 and 1200 °C, magnetic Bragg peaks arising from crystalline magnetite of at least 20 nm in size were observed. In the latter sample the formation of non-magnetic substance, mostly hematite, was observed. These findings are consistent with the results of the magnetization measurement and X-ray diffraction.