Thickness dependence of Morin transition temperature in iridium-doped hematite layers studied through nuclear resonant scattering

The Morin transition of very thin Ir-doped α-Fe₂O₃ films, which is not detectable with conventional magnetization measurements, was studied by conversion electron Mössbauer spectroscopy using a ⁵⁷Co source and nuclear resonant scattering using a synchrotron light source. It was found that (i) the Morin transition temperature increases as the Ir ratio increases, (ii) it decreases when the film thickness decreases, and (iii) the transition becomes irreversible when Ir ratio is small and the thickness is thin. These tendencies were found reproducible and systematic, although the mechanisms are to be clarified by further studies.