Field-induced first-order moment reorientation transitions in R₂T₁₇ ferrimagnets

The basal-plane anisotropy in a hexagonal easy-plane ferrimagnetic system yields discontinuities in the magnetisation curve for external fields applied in the easy plane. At the discontinuities first-order moment reorientation (FOMR) transitions occur. The lowest transition field depends strongly on the difference between the values of the sublattice magnetisations and is very sensitive to the intersublattice coupling. The transition field provides a direct method for evaluating the exchange coupling between the 3d and 4f spins. The lowest transition field in the series of the easy-plane R₂T₁₇ compounds (where R=rare-earth metal and T=Fe, Co) occurs for Ho₂Co₁₇ and amounts to 21 T.