Magnetic anisotropy of half-metallic Co2FeAl ultra-thin films epitaxially grown on GaAs(001)

Bolin Lai,Xianyang Lu,Yongbing Xu,Long Yang,Liang He,Wenqing Liu,Yequan Chen,Junlin Wang,Xuezhong Ruan,Bo Liu,Fengqiu Wang,Jun Du,Yafei Zhao,Xuefeng Wang,Xiaoqian Zhang,Yao Li

doi:10.1063/1.5087227

Abstract

Single crystalline Co2FeAl films with different thicknesses varying from 3.6 to 10.6 nm have been grown on GaAs (001) using Molecule Beam Epitaxy (MBE). The magnetic characteristics were investigated by in-situ magneto-optical Kerr effect (MOKE). For all the samples, the angle dependent magnetization energy has a relatively high and steep peak around [110] direction which is the hard axis, and a wide basin from [11¯0] to [100] which is the range of the easy axis. More interestingly, the magnetic anisotropy includes a strong uniaxial component due to the Co2FeAl/GaAs interface, a cubic one from Co2FeAl crystalline structure, and an unexpected localized anisotropy term around the [110] direction. All the three anisotropy components overlap their own hard axis around [110] direction resulting in a steep energy barrier, which leads to unusual inverted hysteresis loops around [110]. Our findings add a building block for using half-metallic Co2FeAl thin films in the application of magnetic storage devices.

Highlights

Half metallic ferromagnets (HMFs) are ideal materials to be employed in spintronic devices since they possess 100% spin polarization at the Fermi level.1 Among HMFs, Co2FeAl (CFA) as one kind of Heusler alloys at present is one of the most promising spintronic materials because of its very low Gilbert damping constant2 and high Curie temperature (∼1000K).3 Recently, a giant tunnel magnetoresistance (TMR) ratio of 360% at room temperature has been reported on the magnetic tunnel junctions (MTJs) of Cr/CFA(30)/MgO(1.8)/CoFe(0.5)/CFA(5).4 the use of CFA as a ferromagnetic (FM) electrode in devices needs precise knowledge and control of its magnetic properties
All the three anisotropy components overlap their own hard axis around [110] direction resulting in a steep energy barrier, which leads to unusual inverted hysteresis loops around [110]
A giant tunnel magnetoresistance (TMR) ratio of 360% at room temperature has been reported on the magnetic tunnel junctions (MTJs) of Cr/CFA(30)/MgO(1.8)/CoFe(0.5)/CFA(5)

Summary

INTRODUCTION

Half metallic ferromagnets (HMFs) are ideal materials to be employed in spintronic devices since they possess 100% spin polarization at the Fermi level. Among HMFs, Co2FeAl (CFA) as one kind of Heusler alloys at present is one of the most promising spintronic materials because of its very low Gilbert damping constant and high Curie temperature (∼1000K). Recently, a giant tunnel magnetoresistance (TMR) ratio of 360% at room temperature has been reported on the magnetic tunnel junctions (MTJs) of Cr/CFA(30)/MgO(1.8)/CoFe(0.5)/CFA(5) (unit: nm). the use of CFA as a ferromagnetic (FM) electrode in devices needs precise knowledge and control of its magnetic properties. Half metallic ferromagnets (HMFs) are ideal materials to be employed in spintronic devices since they possess 100% spin polarization at the Fermi level.. Among HMFs, Co2FeAl (CFA) as one kind of Heusler alloys at present is one of the most promising spintronic materials because of its very low Gilbert damping constant and high Curie temperature (∼1000K).. The use of CFA as a ferromagnetic (FM) electrode in devices needs precise knowledge and control of its magnetic properties. In this sense, one of the key parameters is the magnetic anisotropy, which is influenced by the substrate, orientation, growth temperature and thickness.. The magnetic anisotropy of such ultra-thin CFA films needs further investigation The magnetic anisotropy of CFA was mainly studied on thick CFA films. CFA as a free layer in MTJ is usually of only several nanometers thickness. the magnetic anisotropy of such ultra-thin CFA films needs further investigation

EXPERIMENTAL DETAILS

CONCLUSIONS