Methods to induce perpendicular magnetic anisotropy in full-Heusler Co2FeSi thin layers in a magnetic tunnel junction structure

TL;DR

This paper develops methods to induce perpendicular magnetic anisotropy in full-Heusler Co2FeSi layers within magnetic tunnel junctions, enhancing their potential for spintronic applications.

Contribution

It introduces specific processing techniques, including oxygen exposure and annealing, to achieve PMA in Co2FeSi layers in MTJ structures, which was not previously demonstrated.

Findings

Oxygen exposure effectively induces PMA in bottom CFS layers.

Annealing at 300°C enhances PMA in top CFS layers.

PMA observed in multilayers with specific layer structures and processing conditions.

Abstract

In this study, to obtain perpendicular magnetic tunnel junctions (p-MTJs) using half-metallic ferromagnets (HMFs), several methods were developed to induce perpendicular magnetic anisotropy (PMA) in full-Heusler Co2FeSi (CFS) alloy thin layers in an MTJ multilayer composed of a layered CFS/MgO/CFS structure. Oxygen exposure at 2.0 Pa for 10 min after deposition of the bottom CFS layer was effective for obtaining PMA in the CFS layer. One of the reasons for the PMA is the formation of nearly ideal CFS/MgO interfaces due to oxygen exposure before the deposition of the MgO layer. The annealing process was effective for obtaining PMA in the top CFS layer capped with a Pd layer. PMA was clearly observed in the top CFS layer of a Cr(40 nm)/Pd(50 nm)/bottom CFS(0.6 nm)/MgO(2.0 nm)/top CFS(0.6 nm)/Pd(10 nm) multilayer, where the top CFS and Pd thin films were deposited at RT and subsequently annealed at 300{\deg}C. In addition to the continuous layer growth of the films, the crystalline orientation alignment at the top CFS/Pd interface probably attributes to the origin of PMA at the top CFS layer.