Prediction of Novel 2D Intrinsic Ferromagnetic Materials with High Curie Temperature and Large Perpendicular Magnetic Anisotropy

Two-dimensional intrinsic ferromagnets with high Curie temperature and large perpendicular magnetic anisotropy (PMA) are promising candidates for data storage and spintronics applications. In this work, first-principle calculations and Monte Carlo simulation are used to investigate the stability, electronic structure, and magnetic anisotropy of monolayers of CrSeX (X = Cl, Br, I). It is found that monolayer CrSeX (X = Cl, Br, I) species are two-dimensional intrinsic ferromagnets and are thermally stable at room temperature. It is worth noting that the Curie temperatures of monolayer CrSeX (X = Cl, Br, I) can reach or even exceed room temperature, and a strong PMA can be obtained in monolayer CrSeI. Interestingly, the PMA of monolayer CrSeI is mainly provided by the nonmetallic I atom with large spin-orbit coupling and magnetic anisotropy of the nonmetallic I atom reaching up to 0.572 meV/I atom, which is comparable to that of metallic Fe atoms at Fe/MgO interfaces. In contrast to monolayer CrSeI, monolayer CrSeCI and CrSeBr possess weak in-plane magnetic anisotropy, and their easily magnetized direction is the [100] axis. By analyzing the projected density of states and the p-orbital-resolved magnetic anisotropy energy of the nonmetallic I atom based on second-order perturbation theory, we find that the large PMA of monolayer CrSeI is mainly provided by the matrix element difference between the spin-up p(x) and p(y) states of the nonmetallic I atoms, and the difference between it and the matrix element difference between the spin-up p(x) and p(y) states of the nonmetallic I atoms in the case of the magnetic moment aligning [100] and [010] axes is the reason why the energy of monolayer CrSeI for the magnetic moment aligning [100] axis is smaller than the energy for the magnetic moment aligning [010] axis. This study suggests that monolayer CrSeI is a promising candidate for future applications in spintronic devices.