Spin-flop transition driven by competing magnetoelastic anisotropy terms in a spin-spiral antiferromagnet

摘要

Holmium, the archetypical system for spin-spiral antiferromagnetism, undergoes an in-plane spin-flop transition earlier attributed to competing symmetry-breaking and fully symmetric magnetoelastic anisotropy terms [Phys. Rev. Lett. 94,227204 (2005)], which underlines the emergence of sixfold magnetoelastic constants in heavy rare earth metals, as otherwise later studies suggested. A model that encompasses magnetoelastic contributions to the in-plane sixfold magnetic anisotropy is laid out to elucidate the mechanism behind the spin-flop transition. The model, which is tested in a Ho-based superlattice, shows that the interplay between competing fully symmetric α-magnetoelastic and symmetry-breaking γ-magnetoelastic anisotropy terms triggers the spin reorientation. This also unveils the dominant role played by the sixfold exchange magnetostriction constant, where D_(α2)~(66) ≃ 0.32 GPa against its crystal-field counterpart M_(α2)~(66)≃ -0.2 GPa, in contrast to the crystal-field origin of the symmetry-breaking magnetostriction in rare earth metals.