Prediction of ferromagnetism in MnB and MnC on nonmagnetic transition-metal surfaces studied by first-principles calculations

We propose two-dimensional ferromagnetic nanostructures, i.e., single-layer films of MnB as well as MnC, on the basis of first-principles calculations. The ferromagnetic state is stable in a freestanding MnB monolayer as well as the one on many nonmagnetic metal substrates, including Ag(001). We have identified the mechanism of the itinerant ferromagnetism as the kinetic-energy gain due to the minority-spin hopping of $3d$ electrons in Mn atoms through B atoms. The second-order perturbative analysis treating hybridization as overlap integrals clarifies that the perpendicular magnetic anisotropy in freestanding MnB and MnB/Ag(001) is mainly attributed to virtual transition processes between up-spin occupied states and down-spin unoccupied states. In contrast, the in-plane anisotropy in MnB/Pd(001) comes from virtual transition processes among down-spin occupied states and up-spin unoccupied states.