Authors

Daichi Chiba, Naoya Shibata & Atsushi Tsukazaki 

Abstract

A ferromagnetic (FM)-metal/oxide stack is the key structure determining the performance of spintronic devices. However, the effect of the electronic polarity of the oxide on the magnetic properties of the adjacent FM-metal has not been investigated previously. Here, we report the magnetic and structural properties of Co ultra-thin films sputter deposited directly on the Zn- and O-polar surfaces of ZnO substrates. The magnetic anisotropy and Curie temperature exhibit dramatic polarity-dependent differences for films on these surfaces. Structural analyses reveal that the heterointerface of the Co/O-polar surface is rather diffusive, whereas that of the Co/Zn-polar surface is atomically flat. These results suggest that the surface polarity plays a key role in determining the properties of the film. This novel FM-metal/polar-oxide system is expected to add new functionality to spintronic devices and provide an ideal basis for investigating the effect of a built-in electric field on the magnetism in a metallic monolayer. 

(a) The magnified HAADF-STEM image around the ZnO/Co interface for Zn-polar sample with tCo = 3.6 nm.(b) The FFT intensity map for the corresponding lateral pixels in the STEM image. The colour indicates the intensity (red: high, blue: low). The peak position corresponds to the LAD. The interfacial ML of Co shows exactly the same LAD as the surface Zn of the ZnO substrate.(c) The averaged intensity of the lateral pixels of the STEM image. The intensity just below the interface Co atoms is the weakest in the image. The (d) side view and (e) top view of the schematic image depicting the expected positions of the Co atoms on the Zn-polar surface.

Scientific Reports：http://www.nature.com/articles/srep38005#f7
Tohoku University：http://www.tohoku.ac.jp/japanese/2016/11/press20161129-01.html