Magnetic Properties of Anti-Perovskite Tetracobalt-Nitride Surfaces: a First-Principles Study

Abstract

We investigate the magnetic properties of the Co(4)N (001) surface by using the full-potential linerized augmented plane-wave band method. We consider two possible terminations, i.e., Co-atom-terminated and CoN-atom-terminated surfaces. From the calculations of the magnetic moment and the site-projected spin-polarized density of states of each atom in the systems, which remain very similar to the properties of the Co(4)N bulk structure, we find that surface termination does not influence considerably the magnetic properties of deeper layers in the anti-perovskite Co(4)N (001) surface. The properties of Co atoms in the two outermost layers depend on their position in the unit cell. Co(I)-type atoms, which are at the corners of a cubical unit cell, are distant from N atoms and they retain an isolated character as the Co atoms in Co fcc crystal. Co(II)-type atoms, which occupy the center of the cube faces, interact more strongly with neighboring N atoms. Therefore, the magnetic moment on Co(II) atoms is smaller than that on Co(I) atoms at the surface layer (S). Compared to the values of magnetic moments on the corresponding atoms in the bulk structure, the magnetic moments on the surface Co(I) (S) and Co(II) (S) atoms are larger: 2.01 and 1.55 mu(B), respectively. In tire CoN-terminated surface, the value obtained for Co(II)(S) is 1.61 mu(B). The magnetic properties of the Co(I) atoms, which are barely influenced by the presence of N atoms, do not depend much on the surface termination.