Magnetocaloric properties of the pseudo-binary Er-rich lanthanide dialuminide compounds

The compounds (RE1-xErx)Al2 (where RE=Gd, Ho, Pr for x⩾0.75) were studied experimentally and theoretically in order to evaluate their magnetocaloric properties and suitability for use as working media in magnetic refrigeration devices operating at low temperatures. I propose a theoretical description of these systems which are composed of two rare-earth ions with different total angular momentum (JRE1 and JRE2) Our model Hamiltonian is solved self-consistently, taking into account crystal electric fields, exchange interactions, the Zeeman effect and second-order effects. From the eigenvalues and eigenstates, the partition function from which thermodynamic quantities may be calculated is obtained, including the isothermal magnetic entropy change, ΔSmag. In order to validate the theoretical results, ΔSmag obtained from heat capacity measurements using Maxwell's relations is compared to the calculated one. The results indicate that for Er-rich compositions fairly good agreement between theoretical and experimental ΔSmag is obtained.