Giant Magnetocaloric Effect in Magnets Down to the Monolayer Limit.

2D magnets can 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, it is revealed 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 ( Δ T ad max $\Delta T_{{\rm{ad}}}^{\max }$ ), maximum isothermal magnetic entropy change, and specific cooling power in monolayer CrF 3 are found as high as 11 K, 35 µJ m -2  K -1 , and 3.5 nW cm -2 under a magnetic field of 5 T, respectively. A 2% biaxial and 5% a-axis uniaxial compressive strain can remarkably increase Δ T ad max $\Delta T_{{\rm{ad}}}^{\max }$ 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.