Elastic constant measurements of rare earth transition metal compounds

Abstract

The availability of single crystals of some of the rare earth transition metal compounds has allowed more detailed studies of the elastic and magnetoelastic effects in these materials [1]. Recent developments in this field will be reviewed with particular emphasis on the RCo 2, RFe 2 and RCo 5 compounds. The very large magnetostrictive effects observed in the former two series are reflected in anomalous changes in their elastic properties. Measurements on two compounds will be described in detail. The elastic constants of the cubic Laves phase compound HoCo 2 have been measured as a function of temperature and magnetic field covering both the initial ferrimagnetic ordering at 78 K and the rotation of the magnetic easy direction from [100] to [110] below 16 K [2]. Dramatic softening of acoustic modes is observed in both of these temperature regions. Preliminary measurements will also be presented of the temperature dependence of the elastic constants of NdCo 5, where there is particular interest in the rotation of the easy direction of magnetisation. NdCo 5 which is hexagonal has a magnetic easy hexagonal c-axis at room temperature. Below 290 K the moments move away from the c-axis until at 240 K they are confined to the basal plane. An inspection of earlier work on Gd would indicate strong magnetoelastic interactions in this region.