Thermodynamic properties of a diluted Heisenberg ferromagnet with interaction anisotropy—Magnetocaloric point of view

The thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin S=1/2 with interaction anisotropy in spin space is investigated. The study is aimed at presenting the magnetocaloric properties of such a model, including the entropy and temperature changes in magnetization/demagnetization processes, generalized Grüneisen ratio as well as the quantities characterizing the efficiency of magnetic cooling cycles. The results are obtained using pair approximation (PA) method and extensively compared with the molecular field approximation (MFA) calculations. The importance of interaction anisotropy and site-dilution is discussed. The inadequacy of the MFA approach (even on the qualitative level) is found for selected quantities, while PA provides the results which are consistent with the experimentally observed behavior.

► Thermodynamics of site-diluted ferromagnetic S=1/2 Heisenberg model is investigated.
► Numerous magnetocaloric properties are extensively analyzed.
► Pair approximation results are compared with those of molecular field approximation.
► The importance of interaction anisotropy in spin space and site-dilution is discussed.
► The inadequacy of MFA approach is found for selected quantities.