Spin orientation of hematite (α-Fe2O3) nanoparticles during the Morin transition
ABSTRACT We have synthesized 40-nm-sized hematite particles by the forced hydrolysis of acid Fe3+ solution to investigate the change in spin direction during the Morin transition. Mössbauer spectra were obtained at various temperatures ranging from 4.3 to 300 K. The Morin temperature (TM) was found to be 220 K, which is lower than 263 K of bulk hematite. Fe3+ spins in the 40-nm-sized hematite particle flip from 90° to 28° with respect to the c-axis of hexagonal structure during the Morin transition, which corresponds to the  direction of rhombohedral structure. This is not in agreement with the spin flip from 90° to 0° observed in bulk hematite or sub- and micron-sized particles at T<TM.