Magnetic properties of Y–Fe–O ultrafine particles containing YFe(3+x)O1.5(4+x) synthesized by rf thermal plasma

Y–Fe–O ultrafine particles containing YFe(3+x)O1.5(4+x), ε-Fe2O3, and γ-Fe2O3(Fe3O4) were fabricated using a thermal plasma evaporation method with rf Ar–O2. To determine if YFe(3+x)O1.5(4+x) in the particles is a ferri-, ferro-, or paramagnetic compound at room temperature (R.T.), the magnetic properties of these particles at R.T. were studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrometry. VSM results showed that the saturation magnetization of particles at R.T. increased after the Curie point (CP) measurement at reduced pressure (4×10−3 Pa) from R.T. to an upper limit temperature higher than 460 °C. The saturation magnetization of particles at R.T. after the CP measurement at reduced pressure from R.T. to 700 °C was larger than that from R.T. to 600 °C. In the XRD patterns, the relative quantities of h-YFeO3 and γ-Fe2O3(Fe3O4) to that of YFe(3+x)O1.5(4+x) increased after the CP measurement at reduced pressure from R.T. to 700 °C, indicating that the saturation magnetization at R.T. increased as the relative quantity of γ-Fe2O3(Fe3O4) increased. The relative quantities of h-YFeO3 and γ-Fe2O3(Fe3O4) to that of YFe(3+x)O1.5(4+x) after the CP measurement depended on Fe/Y of the particles, indicating that the increase in saturation magnetization at R.T. after the Curie point measurement depended on the increase in relative quantity of γ-Fe2O3(Fe3O4). Mössbauer spectrometry before and after the CP measurements showed that YFe(3+x)O1.5(4+x) exhibited only a single type of quadrupole splitting and no magnetic splitting, indicating that YFe(3+x)O1.5(4+x) is a paramagnetic compound.