Intermixing Induced Anisotropy Variations in CoB-based Chiral Multilayer Films

TL;DR

This study investigates how atomic intermixing affects magnetic anisotropy in CoB-based multilayer films, revealing stack-dependent variations and effects of thermal annealing on magnetic properties relevant for chiral magnetic textures.

Contribution

It provides new insights into the stack-order dependence of intermixing and its impact on magnetic anisotropy in amorphous CoB multilayers, with implications for magnetic texture control.

Findings

Intermixing varies with stack order, especially with Ir atop CoB.

Magnetic properties change systematically due to CoIr alloying.

Thermal annealing enhances magnetic anisotropy and coercivity.

Abstract

We examine the atomic intermixing phenomenon in three distinct amorphous CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO - which are shown to stabilise room-temperature chiral magnetic textures. Intermixing occurs predominantly between adjacent metallic layers. Notably, it is stack-order dependent, and particularly extensive when Ir sits atop CoB. Intermixing induced variations in magnetic properties are ascribed to the formation of magnetic dead layer arising from CoIr alloying in the metallic stacks. It also produces systematic variations in saturation magnetization, by as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness for the transition from perpendicular to in-plane magnetic anisotropy differs by more than 2x across the stacks. Finally, with thermal annealing treatment over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy increases monotonically across all stacks, coupled with discernibly larger Hc for the metallic stacks. These are attributed to thermally induced CoPt alloying and MgO crystallization in the metallic and oxide stacks, respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its amorphous nature after annealing. Our results set the stage for harnessing the collective attributes of amorphous CoB-based material platforms and associated annealing processes for modulating magnetic interactions, enabling the tuning of chiral magnetic texture properties in ambient conditions.