Giant magnetocaloric effect in magnets down to the monolayer limit

Abstract

Two-dimensional magnets could potentially revolutionize information technology, but their potential application to cooling technology and magnetocaloric effect (MCE) in a material down to the monolayer limit remain unexplored. Herein, we reveal through multiscale calculations the existence of giant MCE and its strain tunability in monolayer magnets such as CrX${}_3$ (X=F, Cl, Br, I), CrAX (A=O, S, Se; X=F, Cl, Br, I), and Fe${}_3$GeTe${}_2$. The maximum adiabatic temperature change ($\Delta T_{\text{ad}}^{\text{max}}$), maximum isothermal magnetic entropy change, and specific cooling power in monolayer CrF${}_3$ are found as high as 11 K, 35 $\mu$Jm${}^{-2}$K${}^{-1}$, and 3.5 nWcm${}^{-2}$ under a magnetic field of 5 T, respectively. A 2% biaxial and 5% $a$-axis uniaxial compressive strain can remarkably increase $\Delta T_{\text{ad}}^{\text{max}}$ of CrCl${}_3$ and CrOF by 230% and 37% (up to 15.3 and 6.0 K), respectively. It is found that large net magnetic moment per unit area favors improved MCE. These findings advocate the giant-MCE monolayer magnets, opening new opportunities for magnetic cooling at nanoscale.