Analytical Solution of Field-Induced Magnetic Transitions in Uniaxial Antiferromagnets-Application to Hematite

The paper presents an analytical solution of the thermodynamic potential of an antiferromagnet (weak ferromagnet) including a second-order anisotropy term (b/4) sin4θ for the critical orientations of the sublattice magnetizations and the critical fields applied in an arbitrary direction. This was applied to the antiferromagnetic-to-weak-ferromagnetic phase transitions induced in hematite by external fields applied below the Morin point.