Paper NM-MoM2
Effect of Segregation of sp-Impurities on Surface and Grain Boundary Magnetism in Nanocrystalline Nickel and Cobalt

Monday, December 12, 2016, 8:20 am, Room Hau

We present a systematic ab initio study of segregation of 12 non-magnetic sp-impurities (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te) at Σ5(210) grain boundary (GB) and (210) free surface (FS) in fcc nanocrystalline ferromagnetic cobalt and nickel and analyze their effect on structure, magnetic and mechanical properties. In nanocrystalline nickel, most of the above impurities nearly kill or substantially reduce the magnetic moments at the FS and, when segregating interstitially (i.e. Si, P, S, Ge, As, Se), also at the GB so that they provide atomically thin magnetically dead layers which may be very desirable in spintronics. We demonstrate that the existence of magnetically dead layers is a common phenomenon at the sp-impurity-decorated GB and FS in nickel. It is caused by a strong hybridization of sp states of the impurities with the d states of nickel and a redistribution of electron states in both majority and minority bands. Reduction of magnetic moments at the Σ5(210) GB in fcc nanocrystalline cobalt is, in absolute values, very similar to that in nickel. However, as the magnetic moment in bulk cobalt is higher, we do not observe magnetically dead layers here. It turns out that by focused impurity segregation we can generate atomically thin magnetic layers with tailored magnetization, which can contribute to a new development of technologically important materials.