A Simple Computational Proxy for Screening Magnetocaloric Compounds

Abstract

Alternating cycles of isothermal magnetization and adiabatic demagnetization applied to a magnetocaloric material can drive refrigeration in very much the same manner as cycles of gas compression and expansion. The material property of interest in finding candidate magnetocaloric materials is ΔS<sub>M</sub>, their gravimetric entropy change upon application of a magnetic field under isothermal conditions. There is, however, no general method for screening materials for such an entropy change without actually performing the relevant, time- and effort-intensive magnetic measurements. Here we propose a simple computational proxy based on performing nonmagnetic and magnetic density functional theory calculations on magnetic materials. This proxy, which we term the magnetic deformation Σ<sub>M</sub>, is a measure of how much the unit cell deforms comparing with the relaxed structures with and without the inclusion of spin polarization. Σ<sub>M</sub> appears to correlate very well with experimentally measured magnetic entropy change values. Here, the proxy has been tested against 33 ferromagnetic materials with known ΔS<sub>M</sub>, including nine materials newly measured for this study. It has then been used to screen 134 ferromagnetic materials for which the magnetic entropy has not yet been reported, identifying 30 compounds as being promising for further study. As a demonstration of the effectiveness of our approach, we have prepared one of these compounds and measured its isothermal entropy change. MnCoP, with a T<sub>C</sub> of 575 K, shows a maximal ΔS<sub>M</sub> of –6.0 J kg<sup>–1</sup> K<sup>–1</sup> for an H = 5 T applied field.