Ultrathin Co-O oxide layer-driven perpendicular magnetic anisotropy in a CoO/[Co/Pd]m multilayer matrix upon annealing.

Woo Seong Chung,Tae Whan Kim,Seung Mo Yang,Jin Pyo Hong

doi:10.1038/srep37503

Abstract

Ferromagnetic/noble metal multilayer (ML) frames are expected to serve as reliable building blocks in a variety of perpendicular magnetic anisotropy (PMA) based spintronic devices. However, ultrathin ML matrices are highly susceptible to unintended reduction of electron spin polarization in the as-grown or annealed states and often require a large repeat number. Here, we introduce a simple approach to achieve thermally stable PMA in ultrathin [Co/Pd]3 MLs involving the incorporation of an ultrathin CoO capping layer. The thickness and oxygen content of the CoO layer are critical parameters to achieve enhanced PMA in ultrathin [Co/Pd]3/CoO MLs post-annealed up to 400 °C. An extensive analysis of structural features identified that robust PMA characteristics in [Co/Pd]3/CoO MLs are linked with thermally activated oxygen atom diffusion leading to structural reconfiguration upon annealing. The possible origin of the enhanced PMA in our [Co/Pd]3/CoO ML samples after high-temperature annealing is discussed, thereby enabling their use in future spintronic-related devices.

Highlights

Proper capping/buffer layer[13,14]
We show that the enhanced perpendicular magnetic anisotropy (PMA) in ultrathin CoOx-capped ML frames likely arises from atomic ML reconstruction induced by oxygen atom diffusion during high-temperature annealing
We report PMA in ultrathin [Co/Pd]3 MLs upon incorporation of a CoO capping layer after high-temperature annealing

Summary

Introduction

Proper capping/buffer layer[13,14]. We report a simple CoO capping approach which results in appreciable PMA in an ultrathin [Co/Pd]3 ML matrix after high-temperature annealing. The thickness and oxygen content of the incorporated CoO layer are critical to achieving strong PMA. Magnetic and structural characteristics were analyzed by vibrating sample magnetometer (VSM) and high-resolution X-ray diffraction (HR-XRD), respectively. Atomic depth profile analyses of oxygen and cobalt species were conducted by X-ray photoemission spectroscopy (XPS). We show that the enhanced PMA in ultrathin CoOx-capped ML frames likely arises from atomic ML reconstruction induced by oxygen atom diffusion during high-temperature annealing

Methods

Results

Conclusion