Spin-reorientation transitions in NdCo₅and critical effects on the electrical resistivity temperature derivative

Abstract

High resolution electrical resistivity measurements ( rho d rho /dT) are used to investigate in detail the two spin-reorientation transitions of the hexagonal ferromagnetic NdCo5 compound which occur at TSR1=242 K and TSR2=283 K (T>TSR2 gives spontaneous magnetisation, Ms, parallel to the c axis; TSR1<T<TSR2 gives a conical structure; T<TSR1 produces Ms in the basal plane). The authors have obtained the temperature dependence of the angle theta (TSR1<T<TSR2) using rho (T) data. The results being in fair agreement with theta (T) derived from the anisotropy constants K1 and K2. However, the temperature derivative d rho /dT exhibits new (and very localised) delta -type singularities near TSR1 and TSR2. These new anomalies in d rho /dT are interpreted in terms of lattice softening effects at TSR1 and TSR2 and associated anomalies in the C33 elastic constant.