A magnetic analogue of stereoisomerism : application to helimagnetism in two dimensions

J. Villain

Magnetic systems invariant by a continuous symmetry group (e.g. the Heisenberg and XY models) may have a ground state which exhibits a discrete degeneracy, i.e. the lowest energy states form pockets separated by energy barriers in the phase space. This phenomenon is investigated in detail for the case of an isotropic, bilinear spin Hamiltonian on a Bravais lattice. Apart from spin glasses, which are not considered here, this idea can be applied to magnetism in two-dimensional lattices : two-dimensional, Heisenberg magnets with a discrete ground-state degeneracy are expected to have some kind of long range order below some transition temperature, whereas two-dimensional, conventional ferromagnets are disordered at all finite temperatures.

Mots clés: ferromagnetism; Heisenberg model; spin Hamiltonians

Domaines: Articles anciens

J. Villain. A magnetic analogue of stereoisomerism : application to helimagnetism in two dimensions. Journal de Physique, 1977, 38 (4), pp.385-391. ⟨10.1051/jphys:01977003804038500⟩. ⟨jpa-00208597⟩