Electric field effect on magnetic interactions in ultrathin transition-metal films

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A current challenge in the field of spintronics is the manipulation of localized spin structures such as chiral domain walls, skyrmions, or antiskyrmions in magnetic materials, which is a crucial step towards applications. The use of electric fields is attractive as it provides a means to change magnetic properties locally and at low energy cost. Therefore, there has been a large research effort to control magnetism by electric fields in materials such as ferromagnetic semiconductors, multiferroics and magnetic metals. In metals, the focus has been mainly on the electric-field induced change of the magnetocrystalline anisotropy. In this project we will use a multiscale approach combining density functional theory (DFT) and atomistic spin dynamics simulations to explore the possibility of manipulating localized spin structures at transition-metal interfaces by electric fields. Our focus will be ultrathin transition-metal films at surfaces with ferro- or antiferromagnetic exchange and significant Dzyaloshinskii-Moriya interaction (DMI), which exhibit chiral domain walls or magnetic skyrmions. Based on DFT we will calculate the electric field dependence of the exchange and the DMI as well as the magnetocrystalline anisotropy energy. The electric field induced changes of the magnetic interactions in these systems may allow to write and/or to delete such localized spin structures. We will explore this possibility by atomistic spin dynamics using the magnetic interactions as parametrized from our DFT calculations including the effect of the electric field. The local variation of the electric field on the surface e.g. due to the tip of a scanning tunneling microscope can be included in these simulations. The energy barriers for the collapse or creation of localized spin structures such as skyrmions or antiskyrmions will be obtained by applying the geodesic nudged elastic band (GNEB) method. Harmonic transition-state theory is used to calculate the lifetimes.