Geometric dependence of exchange bias in tilted three-dimensional CoFe/IrMn microwires

TL;DR

This study demonstrates the fabrication and characterization of 3D CoFe/IrMn microwires with controlled inclination angles, revealing how geometric factors influence exchange bias and coercivity in non-planar magnetic structures.

Contribution

It introduces a novel method combining two-photon lithography and sputtering to create 3D magnetic bilayers and systematically investigates the impact of geometry on exchange bias effects.

Findings

Exchange bias varies systematically with inclination angle.

Surface roughness affects magnetic properties in 3D structures.

Growth direction influences magnetic anisotropy in non-planar geometries.

Abstract

The exchange bias (EB) effect, arising from interfacial coupling between ferromagnetic (FM) and antiferromagnetic (AF) layers, induces a unidirectional magnetic anisotropy and underpins a wide range of spintronic functionalities. Extending the EB effect to three-dimensional (3D) architectures enables investigation of interfacial coupling in non-planar structures, which is a key step toward realizing spintronic functionalities beyond planar systems. Achieving this requires the fabrication of FM/AF bilayers with smooth interfaces and well-defined thicknesses on non-planar scaffolds, together with suitable characterization methods. In this work, we realize exchange-biased 3D FM/AF microwires by combining two-photon lithography with magnetron sputtering. CoFe/IrMn bilayers are deposited on microwire scaffolds with inclination angles of 0 deg, 30 deg, 45 deg relative to the substrate, and their magnetization reversal is probed using dark-field magneto-optical Kerr effect (DF-MOKE) magnetometry. We find that the EB and coercive fields vary in a characteristic way with the inclination angle, consistent with the systematic reduction in film thickness expected from inclined directional deposition. In addition, the EB magnitude is influenced by the combined effects of surface roughness of non-planar geometries and the directional growth of the bilayer, highlighting the importance of 3D scaffold surface quality for integrating magnetic multilayers. These results provide insight into the growth and magnetic behavior of sputter-deposited magnetic multilayers with functional interfaces on 3D geometries.