Engineering the magnetic anisotropy axes in epitaxial half-Heusler NiMnSb by Pt and Ta capping

The magnetic anisotropy in NiMnSb has been found to be highly sensitive to layer parameters, such as Mn concentration or thickness. Here, we report on the magnetic anisotropy of thin epitaxial single crystal quality NiMnSb films (3–40 nm) in combination with different capping layer materials, Ru, Pt, and Ta. We observe that the easy axis of the magnetic anisotropy is forced into the $[11¯0]$ crystal direction for Pt capped and into the [110] crystal direction for Ta capped NiMnSb, irrespective of the original anisotropy of the NiMnSb film. This effect is independent of the thickness of the capping layer and even present in multilayers with a Cu interlayer (few nanometers) between the NiMnSb and Pt cap, indicating that it is not related to interface chemistry and possibly pointing to it originating from the strong spin-orbit coupling in the capping layers.