Magnetocaloric effect near room temperature in a freestanding two-dimensional non-van der Waals crystal of MnCoAs

The magnetocaloric effect (MCE) plays a major role in magnetic refrigeration. However, a large MCE near room temperature has rarely been observed in the fast-growing family of two-dimensional (2D) materials. Using 2D non-van der Waals crystals, herein we design an intrinsic and physically realistic system to achieve a large MCE. Based on first-principles calculations, we identify that 2D MnCoAs is a robust ferromagnetic metal, whose specific heat shows anomalous bimodal behavior. The MCE in 2D MnCoAs generates a Curie temperature of 214-221 K, a magnetic entropy change of 1.4-4.3 J kg-1 K-1, a relative cooling power of 28.4-244.5 J kg-1, and a full width at half maximum of the entropy change peak of 20-57 K for a magnetic field change of 1-7 T. For comparison, the value of magnetic entropy change is 0-0.2 J kg-1 K-1 in bulk MnCoAs. Obviously, the reduced dimensionality leads to a significant improvement in the MCE. In addition, 2D MnCoAs is highly ductile, which is conducive to magnetic refrigeration cycling stability. We also show that a 2D MnCoAs crystal can be grown on a Si (001) substrate while it retains its MCE value, paving an avenue to the desired goal of on-chip cooling. Our results provide not only an alternative MCE thin film for cooling applications in nanodevices, but also a fundamental understanding of the impact of reduced dimensionality on MCE.