Thermodynamic properties of a diluted Heisenberg ferromagnet with interaction anisotropy -- magnetocaloric point of view

TL;DR

This paper investigates the thermodynamic and magnetocaloric properties of a site-diluted Heisenberg ferromagnet with interaction anisotropy, using Pair Approximation, highlighting the limitations of Molecular Field Approximation.

Contribution

It introduces the use of Pair Approximation to accurately analyze magnetocaloric effects in anisotropic, diluted Heisenberg ferromagnets, surpassing the Molecular Field Approximation.

Findings

PA results align with experimental observations

Interaction anisotropy significantly affects magnetocaloric properties

MFA is inadequate for certain thermodynamic quantities

Abstract

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 Gr\"uneisen 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 behaviour.