A determination of the magnetoelastic coupling constant Mϵ2 for the rare earth compound ErAl 2

Abstract

The magnetostriction of a single crystal of ErAl 2 has been measured in the ordered and paramagnetic phases along the [111] easy axis of magnetization. The coupling constant M ϵ 2 between the rhombohedral distortion and the magnetization process has been determined by fitting the measured strain to a single-ion Hamiltonian which includes crystal field, exchange, magnetoelastic and elastic terms. In the crystal field term, revised values of the cubic crystal field parameters, B 0 4, B 0 6, obtained from neutron spectroscopy, have been used. The observed temperature dependence of the strain ϵ ϵ 2 is also shown to be well described by the molecular field approximation of Callen and Callen and a calcualtion of M ϵ 2 based on the point charge model predicts both the sign and magnitude of the coupling constant.