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 CrX₃ (X = F, Cl, Br, I), CrAX (A = O, S, Se; X = F, Cl, Br, I), and Fe₃ GeTe₂ . The maximum adiabatic temperature change ( $$ ), maximum isothermal magnetic entropy change, and specific cooling power in monolayer CrF₃ are found as high as 11 K, 35 µJ m^-2  K^-1 , and 3.5 nW cm^-2 under a magnetic field of 5 T, respectively. A 2% biaxial and 5% a-axis uniaxial compressive strain can remarkably increase $$ of CrCl₃ 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.