Magnetoelectric control of surface anisotropy and nucleation modes in L1₀-CoPt thin films

The interplay between electric field controlled surface magnetic anisotropy and micromagnetic nucleation modes for L10-CoPt thin-film is investigated with density-functional and micromagnetic model calculations. The electric field redistributes electron states near the Fermi level, which has a fairly strong effect on the surface anisotropy, but due to inversion symmetry, the net anisotropy of the films with odd numbers of layers remains unchanged. By contrast, the micromagnetic nucleation mode is spatially asymmetric even for symmetric thin-films with odd numbers of layers. This leads to a reduction of the nucleation field (coercivity) and — for suitably chosen nanostructures — to substantial changes in the hysteretic behavior. In lowest order, the coercivity reduction is independent of the total film thickness. This counter-intuitive feature can potentially be exploited in magnetoelectric switching devices