engleski

Calculation of magnetocaloric effect in GdGa and some related compounds

The intermetallic compound GdGa is reported to be ferromagnet with two magnetic order transitions ; a spin reorientation transition at T_SR ~ 100 K and a ferromagnetic-paramagnetic transition at T_C ~ 180 K. It also showed a magnetocaloric effect (MCE) which is of potential interest in magnetic refrigeration study. Substitution of Ga with some nearby elements (Ge, Zn, Cu) can strongly infuence the magnetic order, and therefore the thermodynamic properties of the prototype compound. The influence of substitution in tuning such properties is useful in studying the MCE and the mechanism of mediating exchange interactions through nonmagnetic atoms. In this work we presented preliminary results of calculations of the MCE, in terms of the isothermal magnetic entropy changes ∆S_mag and the adiabatic temperature changes ∆T_ad, in GdGa, GdGa(1-x)Ge(x), 0 < x < 1, and in Gd(Zn, Cu) compounds, under the magnetic field changes from 0->5T. Calculations are based on the mean-field model of coupled magnetic lattices combined with the density functional theory (DFT). Lattice contribution to total entropy is added in Debye approximation. In brief, we wanted to show how mean-field model accompanied with DFT calculation of exchange coupling constants could be used in prediction of the transition ordering temperature and the MCE. Results of the calculations are compared with experimental values. The role and dependence of conduction electron mediated exchange on chemical composition is discussed.

magnetocaloric effect; intermetallic compounds

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