The influence of spontaneous and field-induced spin reorientation transitions on the magnetocaloric properties of HoZn and ErZn

Abstract

We report a theoretical investigation on the magnetocaloric properties of the cubic CsCl-type HoZn and ErZn compounds. Several anomalies in the magnetocaloric quantities, ΔST and ΔTS, are observed due to spontaneous and/or field-induced spin reorientation transitions in these compounds. In HoZn, a discontinuity in the isothermal entropy change and in the adiabatic temperature change around T1 = 23 K is ascribed to the spontaneous reorientation transition. Under a magnetic field variation from 0 up to 2 T in the 〈110〉 and 〈100〉 directions, an almost table-like behavior in ΔST is predicted between T1 and TSR1. The peak around the ferromagnetic–paramagnetic transition temperature in the magnetocaloric quantities shows a dependence on the direction of the applied field. For μ0ΔH = 2 T, it reaches 11.9 J/kg K (magnetic field along the 〈111〉 direction) and 7.9 J/kg K (magnetic field in the 〈100〉 direction). In ErZn there is also a dependence of ΔST and ΔTS on field direction. From the analysis of the spin reorientations in both compounds we have built spin reorientation diagrams that summarize their temperature and field dependence. Our theoretical approach is based on a model Hamiltonian that includes exchange, crystal field, and quadrupolar interactions.