Tailoring the magnetic anisotropy of Py/Ni bilayer films using well aligned atomic steps on Cu(001).

S Ma,Z D Zhang,J Li,J X Deng,Z Q Qiu,A Tan,C Hwang

doi:10.1038/srep11055

Abstract

Tailoring the spin orientation at the atomic scale has been a key task in spintronics technology. While controlling the out-of-plane to in-plane spin orientation has been achieved by a precise control of the perpendicular magnetic anisotropy at atomic layer thickness level, a design and control of the in-plane magnetic anisotropy has not yet been well developed. On well aligned atomic steps of a 6° vicinal Cu(001) surface with steps parallel to the [110] axis, we grow Py/Ni overlayer films epitaxially to permit a systematic exploration of the step-induced in-plane magnetic anisotropy as a function of both the Py and the Ni film thicknesses. We found that the atomic steps from the vicinal Cu(001) induce an in-plane uniaxial magnetic anisotropy that favors both Py and Ni magnetizations perpendicular to the steps, opposite to the behavior of Co on vicinal Cu(001). In addition, thickness-dependent study shows that the Ni films exhibit different magnetic anisotropy below and above ~6 ML Ni thickness.

Highlights

The step-induced in-plane magnetic anisotropy cannot be fully studied because of the limited thickness range below the Ni Spin reorientation transition (SRT) thickness
Our result provides a new method for the modulation of the magnetic anisotropy in both the out-of-plane and the in-plane directions which is important to the prospective application in future spintronics devices
According to the general Néel’s expression for the effective anisotropy Keff = KV + 2 KS/d Ref. [32], the competition between the interface and the volume anisotropy energies is responsible for the overall effective uniaxial anisotropy induced by the steps and the interfacial contribution should gradually decrease with increasing the Py thickness

Summary

Introduction

The step-induced in-plane magnetic anisotropy cannot be fully studied because of the limited thickness range below the Ni SRT thickness. Dhesi et al investigated the SRT of Ni film on vicinal Cu(1 1 32) and found a very peculiar behavior that below the SRT thickness, the Ni magnetization is titled from the surface normal direction with the in-plane component perpendicular to the steps above 5.5 ML and switches to in-plane direction and parallel to the steps below 5.5 ML27. It has remained as a mystery on the sign of the step-induced magnetic anisotropy in vicinal Ni/Cu(001): is the easy axis parallel to the steps as in the Co/vicinal Cu(001) or perpendicular to the steps?. Our result provides a new method for the modulation of the magnetic anisotropy in both the out-of-plane and the in-plane directions which is important to the prospective application in future spintronics devices

Methods

Results

Conclusion