Realistic first-principles calculations of the magnetocaloric effect: applications to hcp Gd

Abstract

We present an efficient computational approach to evaluate field-dependent entropy of magnetocaloric materials from ab-initio methods. The temperature dependence is reported for the entropy change, specific heat and magnetization for hcp Gd. To obtain optimal accuracy in the calculations, a mixed-scheme for magnetic Monte Carlo simulations is proposed and found to be superior to using pure quantum or classic statistics. It is demonstrated that lattice and magnetic contributions play a role in the entropy change and that the dominating contribution comes from the magnetic contribution. The total calculated entropy change agrees with measurements at room temperature.

GRAPHICAL ABSTRACT

IMPACT STATEMENT

Demonstration of the accuracy of ab-initio theory, coupled to statistical methods, for accurate calculations of the total entropy variation associated with the magnetic transition of Gd. Reproduction of experimental data of entropy change.

Keywords:

• Magnetocaloric
• Gd
• entropy
• Monte Carlo
• mixed statistics

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 At low temperatures, the magnetic fluctuations can only happen in the directions transverse to the magnetization, i.e. the system has 2 degrees of freedom.

Additional information

Funding

This work was supported by the Swedish Foundation for Strategic Research, within the project Magnetic Materials for Green Energy Technology (ref. EM16-0039), STandUPP, eSSENCE, the Swedish Energy Agency (Energimyndigheten) as well as Vetenskapsrådet. The computations performed in this work were enabled by resources provided by the CSC – IT Center for Science, Finland, for computational resources and by the Swedish National Infrastructure for Computing (SNIC) at NSC and PDC centers, partially funded by the Swedish Research Council through grant agreement no. 2018-05973.