Competing surface and bulk anisotropies in TbCo films

Amorphous TbCo is a ferrimagnet which is well known for its strong perpendicular magnetic anisotropy (PMA). It is central to many devices involving spin-orbit torque, all-optical and thermally induced magnetization switching. In order to achieve the PMA needed for these applications, the thickness of the film needs to exceed a value. This critical thickness depends on the properties of the alloy, such as the size of the anisotropy and magnetostatic energy. However, it has been shown that this critical thickness also depends on seed and/or capping layer, where a significantly lower critical thickness can be achieved by using heavy metals. The dependence of the magnetic properties on the seed and capping layer hints at the existence of an interface layer which does not exhibit PMA. By studying different spin configurations in TbCo thin films with different seed/buffer layers, we will determine the origin of this effect, which in turn will facilitate the optimal design of magnetization switching in this important material system.