Competing interface and bulk anisotropies in Co-rich TbCo amorphous thin films.

We study the magnetic properties of amorphous Tb$_x$Co$_{100-x}$ films with $x$ in the range 8$-$12~at\% and with a thickness of 5$-$100~nm. In this range the magnetic properties are shaped by a competition between a perpendicular bulk magnetic anisotropy and an in-plane interface anisotropy, in addition to the changes in magnetization. This results in a temperature controllable spin reorientation transition from in-plane to out-of-plane which is thickness and composition dependent. Furthermore, we show that perpendicular anisotropy is recovered throughout an entire TbCo/CoAlZr multilayer, where neither TbCo nor CoAlZr single layers exhibit perpendicular anisotropy. This illustrates the important role of the TbCo interfaces in the overall effective anisotropy.