The evolution of in-plane magnetic anisotropy in CoFeB/GaAs(001) films annealed at different temperatures

Hongqing Tu,W Zhang,Biao You,Jun Du,Lujun Wei,Yuan Yuan,Ji Wang

doi:10.1063/1.5004512

Abstract

A considerable in-plane uniaxial magnetic anisotropy (UMA) field (Hu ∼ 300 Oe) could be achieved when the amorphous CoFeB film was deposited on the GaAs(001) wafer by magnetron-sputtering after proper etch-annealed procedure. In order to get deep insights into the mechanism of the UMA, the film was annealed at different temperatures and the evolution of the in-plane magnetic anisotropy was investigated carefully. With increasing the annealing temperature (TA), the UMA could be maintained well when TA reached 250°C, but became very weak at 300°C. However, when TA was elevated to 400°C, another UMA (Hu ∼ 130 Oe) was built accompanied with a fourfold magnetic anisotropy with its strength of about 50 Oe. In terms of the magnetic anisotropy evolution along with TA, the anelastic strain, which is thought to be resulted from the interfacial interaction between CoFeB and GaAs, may play a dominant role in producing the enhanced UMA based on the ‘bond-orientational’ anisotropy (BOA) model.

Highlights

Ferromagnetic (FM) films deposited on semiconductors (SCs) can often exhibit significant uniaxial magnetic anisotropy (UMA), which has important applications in spintronic devices such as information storage and magnetic field sensors
Both cross-sectional transmission electron microscope (TEM) and x-ray diffraction (XRD) results show that the as-deposited CoFeB film is amorphous
The sample was cut into several pieces, and each of them was annealed at a specific temperature for two hours with the ambient pressure lower than 1.0×10-5 Pa

Summary

INTRODUCTION

Ferromagnetic (FM) films deposited on semiconductors (SCs) can often exhibit significant uniaxial magnetic anisotropy (UMA), which has important applications in spintronic devices such as information storage and magnetic field sensors. Two different ideas have emerged about the origin of the UMA: (i) magnetoelastic coupling due to the lattice mismatch between GaAs and the FM layer and resulting anisotropic strain or (ii) electronic hybridization between the FM layer and GaAs.1 These FM films often display fourfold magnetic anisotropy (FMA) at proper thicknesses in the film plane, which is undoubtedly caused by the magneto-crystalline anisotropy (MCA). To our knowledge, the anelastic strain is temporarily nonrecoverable, for example, after removing stress but, in many cases, may be recoverable by annealing.14,18 If this argument is true, the UMA in the CoFeB/GaAs(001) film, which is currently considered to result from the anelastic strains, will weaken remarkably or even vanish after proper annealing. In order to get deep insights of the UMA mechanism, the CoFeB/GaAs(001) film owning enhanced UMA at the as-deposited state was annealed at different temperatures, and the evolution of the in-plane magnetic anisotropy along with the annealing temperature (T A) was investigated carefully

EXPERIMENTAL RESULTS

RESULTS AND DISCUSSION

CONCLUSIONS