Ion-lattice interactions in rare earth compounds

Abstract

A study is made using a variational method, of the interaction of a dysprosium ion in an axially symmetric crystal field with a lattice distortion which gives a coupling of type epsilon Q(J₊²+J_-²). It is shown that a low energy configuration can be obtained in which the dysprosium moment lies in, or near, the perpendicular plane is accompanied by static strain in the lattice. Several orientations of moment plus strain have equal energies. It is then shown that in a magnetically concentrated crystal there will be mutual energies coming from the strains, and it is suggested that the unusual properties of dysprosium vanadate can be understood as arising from ordering of the lattice strains at low temperatures.