Anisotropic magnetocaloric effect in single crystals of CrI$_3$

TL;DR

This study investigates the anisotropic magnetocaloric effect in CrI$_3$ single crystals, revealing a two-step magnetic transition, localized magnetism, and quantifying the magnetic entropy change and cooling power under various magnetic fields.

Contribution

It provides a detailed analysis of the anisotropic magnetocaloric effect and magnetic transitions in CrI$_3$, including experimental measurements and scaling analysis, which is novel for this material.

Findings

Maximum magnetic entropy change of ~5.65 J/kg·K at 9 T

Anisotropy in entropy change with a maximum difference of ~1.56 J/kg·K between axes

Second-order magnetic transition confirmed by universal scaling of entropy change

Abstract

We report a systematic investigation of dc magnetization and ac susceptibility, as well as anisotropic magnetocaloric effect in bulk CrI$_3$ single crystals. A second-stage magnetic transition was observed just below the Curie temperature $T_c$, indicating a two-step magnetic ordering. The low temperature thermal demagnetization could be well fitted by the spin-wave model rather than the single-particle model, confirming its localized magnetism. The maximum magnetic entropy change $-\Delta S_M^{max} \sim 5.65$ J kg$^{-1}$ K$^{-1}$ and the corresponding adiabatic temperature change $\Delta T_{ad} \sim 2.34$ K are achieved from heat capacity analysis with the magnetic field up to 9 T. Anisotropy of $\Delta S_M(T,H)$ was further investigated by isothermal magnetization, showing that the difference of $-\Delta S_M^{max}$ between the $ab$ plane and the $c$ axis reaches a maximum value $\sim$ 1.56 J kg$^{-1}$ K$^{-1}$ with the field change of 5 T. With the scaling analysis of $\Delta S_M$, the rescaled $\Delta S_M(T,H)$ curves collapse onto a universal curve, indicating a second-order type of the magnetic transition. Furthermore, the $-\Delta S_M^{max}$ follows the power law of $H^n$ with $n = 0.64(1)$, and the relative cooling power RCP depends on $H^m$ with $m = 1.12(1)$.