Tailoring Ultrathin Magnetic Multilayers at Terraced Topologically Insulating Interfaces for Perpendicularly Magnetized Domains

TL;DR

This study develops a method to grow ultrathin magnetic multilayers on topological insulator interfaces, achieving uniform perpendicular magnetic domains suitable for spintronics, by optimizing buffer layer thickness and structure.

Contribution

It introduces a novel heterostructure combining topological insulators with magnetic multilayers, demonstrating how buffer layer optimization enables perpendicular magnetic anisotropy.

Findings

Buffer layer thickness is critical for uniform perpendicular magnetic anisotropy.

Buffered samples show well-defined out-of-plane magnetic domains.

Optimized heterostructures are suitable for spin-orbit torque applications.

Abstract

Topological insulators and skyrmion-hosting, chiral magnetic multilayers are two well-explored areas of modern condensed matter physics, each offering unique advantages for spintronics applications. In this paper, we demonstrate the optimization process for the growth of a Bi$_2$Se$_3$/buffer/[Pt/CoB/Ru]$_{\times N}$ heterostructure that combines these two material classes: the Bi$_2$Se$_3$ epilayer was grown by molecular beam epitaxy before transfer under ultrahigh vacuum to a separate growth chamber where the polycrystalline metallic multilayer was sputter deposited. The structure of the samples was characterized by co-fitted X-ray and polarized neutron reflectometry measurements and scanning transmission electron microscopy. Polarized neutron models and standard magnetometry show that a buffer layer exceeding a critical thickness is required to obtain the desired uniform, perpendicular magnetic anisotropy in every magnetic layer in the multilayer. Samples with both Ta and Mo buffers were used requiring thicknesses of 1.5 and 0.9 nm respectively. In minimizing the Bi$_2$Se$_3$ terracing, buffered samples yield well-defined, out-of-plane, magnetic domains suitable for spin-orbit torque induced manipulation as determined by X-ray photoemission electron microscopy.