Density functional theory study of the magnetic properties of 2D ferromagnetic semiconductor CrCl3-xBrx (x = 1-3) monolayers.

Two-dimensional ferromagnetic semiconductors have attracted great attention due to their applications in the next generation of nanoscale spintronics. However, experimentally confirmed two-dimensional ferromagnetic semiconductors are rather limited and suffer from a rather low Curie temperature. Based on density functional theory, the structure, electronic, and magnetic properties of the CrCl3-xBrx (x = 0, 1, 2, 3) monolayers are systematically explored. As a result, they are all semiconductors with intrinsic ferromagnetism, and their band gaps decrease with increasing Br composition. Interestingly, due to the joint effects of spin-orbit coupling and magnetic dipole-dipole interaction, the magnetic easy axes have a transition from in-plane to out-of-plane with Br composition increasing. In addition, by the isovalent alloying method, the FM coupling of CrCl3-xBrx can be remarkably enhanced, and their Curie temperature can be increased to 120 K, 130 K, 145 K and 170 K without introducing any carriers, respectively. Besides, the CrCl3-xBrx monolayers have good thermal and dynamical stability, and their small exfoliation energies confirm that they can be exfoliated from the bulk flexibly. Our findings not only provide an effective method to improve ferromagnetism in 2D semiconductors but also provide a class of potential candidates for realistic spintronic applications.