Neutron Diffraction Study of the Magnetic Structure of Hematite to 41 kbar

Time-of-flight neutron diffraction has been used to study the pressure dependence of the magnetic moment direction in α-Fe₂{O}₃$ to 41 kbar. The pressure dependence of the magnetic moment direction at room temperature is found to be in agreement with the pressure dependence calculated from measurements of the quadrupole splitting at high pressure by Vaughan and Drickamer, using the M\"ossbauer effect. It is found that the spin direction varies slowly and continuously with pressure above 14 kbar, with no well-defined Morin transition occurring at room temperature. The large pressure dependence of the Morin transition at lower pressures is well accounted for by Searle's theory based on the magnetoelastic effect. The slow variation of the spin direction at higher pressures must be accounted for by higher-order contributions to the anisotropy energy.