Crystalline structure and XMCD studies of Co40Fe40B20 grown on Bi2Te3, BiTeI and Bi2Se3

TL;DR

This study investigates the epitaxial growth, crystalline structure, and magnetic properties of CoFeB films on topological insulator substrates Bi2Te3, Bi2Se3, and BiTeI, revealing ordered ferromagnetic films and their magnetic characteristics.

Contribution

First demonstration of structurally ordered ferromagnetic CoFeB films on topological insulator surfaces using laser MBE, with detailed analysis of their structure and magnetic moments.

Findings

Epitaxial CoFeB films on Bi2Te3 show Bcc(111) structure.

CoFeB on Bi2Se3 is polycrystalline at RT.

Magnetic anisotropy differs between CoFeB/Bi2Te3 and CoFeB/Bi2Se3.

Abstract

Epitaxial films of Co40Fe40B20 (further - CoFeB) were grown on Bi2Te3(001) and Bi2Se3(001) substrates by laser molecular beam epitaxy (LMBE) technique at 200-400C. Bcc-type crystalline structure of CoFeB with (111) plane parallel to (001) plane of Bi2Te3 was observed, in contrast to polycrystalline CoFeB film formed on Bi2Se3(001) at RT using high-temperature seeding layer. Therefore, structurally ordered ferromagnetic thin films were obtained on the topological insulator surface for the first time. Using high energy electron diffraction (RHEED) 3D reciprocal space mapping, epitaxial relations of main crystallographic axes for the CoFeB/ Bi2Te3 heterostructure were revealed. MOKE and AFM measurements showed the isotropic azimuthal in-plane behavior of magnetization vector in CoFeB/ Bi2Te3, in contrast to 2nd order magnetic anisotropy seen in CoFeB/Bi2Se3. XPS measurements showed more stable behavior of CoFeB grown on Bi2Te3 to the oxidation, in compare to CoFeB grown on Bi2Se3. XAS and XMCD measurements of both concerned nanostructures allowed calculation of spin and orbital magnetic moments for Co and Fe. Additionally, crystalline structure and XMCD response of the CoFeB/BiTeI and Co55Fe45/BiTeI systems were studied, epitaxial relations of main crystallographic axes were found, and spin and orbital magnetic moments were calculated.