Anisotropic magnetocaloric effect of CrI$_{3}$: A theoretical study

TL;DR

This study provides a theoretical analysis of the anisotropic magnetocaloric effect in CrI₃, highlighting the role of magnetic anisotropy energy and susceptibility in thermodynamic behavior near the Curie temperature.

Contribution

The paper introduces a theoretical framework combining Heisenberg Hamiltonian derivation and Monte Carlo simulations to analyze anisotropic magnetocaloric effects in CrI₃.

Findings

Negative sign of isothermal magnetic entropy change along the hard plane was reproduced.

Magnetocrystalline anisotropy energy significantly influences temperature-dependent entropy changes.

High magnetic susceptibility occurs due to competition between anisotropy energy and external magnetic field at low temperatures.

Abstract

CrI$_{3}$ is considered to be a promising candidate for spintronic devices and data storage. We derived the Heisenberg Hamiltonian for CrI$_{3}$ from density functional calculations using the Liechtenstein formula. Moreover, the Monte--Carlo simulations with the Sucksmith--Thompson method were performed to analyze the effect of magnetic anisotropy energy on the thermodynamic properties. Our method successfully reproduced the negative sign of isothermal magnetic entropy changes when a magnetic field was applied along the hard plane. We found that the temperature dependence of the magnetocrystalline anisotropy energy is not negligible at temperatures slightly above the Curie temperature. We clarified that the origin of this phenomenon is attributed to anisotropic magnetic susceptibility and magnetization anisotropy. The difference between the entropy change of the easy axis and the hard plane is proportional to the temperature dependence of the magnetic anisotropy energy, implying that the anisotropic entropy term is the main source of the temperature dependence of the free energy difference when magnetizing in a specific direction other than the easy axis. We also investigated the magnetic susceptibility that can be used for the characterization of the negative sign of the entropy change in the case of a hard plane. The competition of magnetocrystalline anisotropy energy and external magnetic field at low temperature and low magnetic field region causes a high magnetic susceptibility as the fluctuation of magnetization. Meanwhile, the anisotropy energy is suppressed at a sufficient magnetic field applied along the hard axis, the magnetization is fully rotated to the direction of the external magnetic field.