Impurities and pressure effects on the entropy change of rare earth based compounds*

In this work, we theoretically discuss the effects of impurities and external pressure on the entropy change and on the temperature change of metallic compounds, whose magnetism comes mainly from rare earth ions. To this end we use a Hamiltonian of 4f localized interacting magnetic moments including extra terms to take into account the magnetoelastic interaction and anisotropy [1]. We apply the model to describe the entropy change in R₅Si₂Ge₂ (R=Gd, Tb) and Er(Co_1-xSi_x)₂. Our results show that applied pressure reduces the critical temperature of R₅Si₂Ge₂ but keeps the peak of the entropy change almost constant. On the contrary, applied pressure increases both the critical temperature of Tb₅Si₂Ge₂ and the entropy change around it. This finding is in good agreement with the available experimental data [2]. Similar results obtained for Er(Co_1-xSi_x)₂ are also in agreement with available experimental data
[1] N. A de Oliveira P. J. Von Ranke Phys. Rep. 489 (2010) 89
[2] S. Yuce et al APPL. Phys. Let. 101 (2012) 071906