Polycrystalline Co2Fe0.4Mn0.6Si Heusler alloy thin films with high B2 ordering and small magnetic anisotropy for magnetic tunnel junction based sensors

Nana Kudo,Yasuo Ando,Masakiyo Tsunoda,Mikihiko Oogane

doi:10.1063/1.5130461

Abstract

To measure the bio magnetic field from the heart and brain at room temperature, the magnetic tunnel junctions (MTJs) based sensor is required to achieve a high sensitivity which is defined as the TMR ratio/2Hk (where Hk is anisotropic magnetic field of the free layer). To realize both high TMR ratio and small Hk, we employed (001)-oriented polycrystalline Co-based Heusler alloy material (Co2Fe0.4Mn0.6Si) for the free layer which is known for its high spin polarization and small Hk. In this study, we optimized the crystal and magnetic properties of Co2Fe0.4Mn0.6Si free layer and succeeded in reducing Hk in polycrystalline CFMS free layer with high B2 ordering. We also demonstrated the linear output of TMR in MTJs fabricated under the optimized condition.

Highlights

Magnetic tunnel junctions (MTJs) attract great interest for application to some spintronics devices, such as a highly sensitive magnetic sensor, because of the large tunnel magnetoresistance (TMR) effect
To measure the bio magnetic field from the heart and brain at room temperature, the magnetic tunnel junctions (MTJs) based sensor is required to achieve a high sensitivity which is defined as the TMR ratio/2Hk
Since the sensitivity of MTJs based sensors is defined as the TMR ratio/2Hk (Hk: magnetic anisotropy field), small Hk in the free layer and high TMR ratio is required to achieve the high sensitivity

Summary

Introduction

Magnetic tunnel junctions (MTJs) attract great interest for application to some spintronics devices, such as a highly sensitive magnetic sensor, because of the large tunnel magnetoresistance (TMR) effect. We have demonstrated detection of the weak bio magnetic field at room temperature using MTJs based magnetic sensor devices.. The detection of the magnetic field from the heart was succeeded by real-time measurement, the sensitivity of the MTJs based sensor is still short for detection of the brain field. Since the sensitivity of MTJs based sensors is defined as the TMR ratio/2Hk (Hk: magnetic anisotropy field), small Hk in the free layer and high TMR ratio is required to achieve the high sensitivity. Epitaxially grown free layer is not suitable for the MTJs sensor application and polycrystalline structure is useful for the reduction of Hk by averaging the crystalline magnetic anisotropy in the film plane. In order to achieve a high TMR ratio, Co-based Heusler alloy is a candidate for free layer material because of its high spin polarization and small magnetic anisotropy.

Methods

Results

Conclusion