Large magnetic anisotropy and its strain modulation in two-dimensional intrinsic ferromagnetic monolayer RuO2 and OsO2

Abstract

As a promising candidate suitable for applications in spintronic devices at the nanoscale and in high-density data storage, two-dimensional (2D) intrinsic ferromagnetic materials with magnetic anisotropy (MA) have been experimentally demonstrated in the last year. Monolayer RuO₂ and OsO₂ hold great potential for achieving large MA due to the strong spin–orbit coupling (SOC) interactions of Ru and Os. Using first-principles calculations, we systematically investigate the stability, electronic structure and magnetic properties of monolayer 1T-RuO₂ and 1T-OsO₂ and explore the effects of strain on their electronic structure and magnetic properties. It is found that both monolayer 1T-RuO₂ and 1T-OsO₂ are 2D intrinsic ferromagnetic materials with large MA. In particular, the magnetic anisotropy energy (MAE) of monolayer 1T-OsO₂ is as high as −42.67 meV per unit cell and its Curie temperature is much higher than the liquid-nitrogen temperature. It is worth noting that the large MA of monolayer 1T-OsO₂ is significantly enhanced by tensile strain. By analyzing the density of states and the d orbital-resolved MAE of Os and Ru atoms based on second-order perturbation theory, it is revealed that the large MAE of monolayer 1T-RuO₂ and 1T-OsO₂ is mainly contributed by the matrix element differences between the opposite-spin d_xy and d_x²−y² orbitals of Ru and Os atoms, and the tensile strain induced enhancement of monolayer 1T-OsO₂ mainly originates from the change in contributions to the MA from the matrix element differences between the d_yz and d_z² orbitals of Os atoms from zero to negative. Our results indicate that monolayer 1T-RuO₂ and especially monolayer 1T-OsO₂ are promising candidates suitable for applications in spintronic devices at the nanoscale and in high-density data storage.