Local breaking of the spin-orbit interaction: the microscopic origin of exchange bias in Co/FeMn

TL;DR

This paper reveals that the orbital magnetic moment in Co/FeMn thin films is the key microscopic factor causing exchange bias, advancing understanding of interfacial magnetic interactions.

Contribution

It provides the first direct spectroscopic evidence linking the orbital magnetic moment to exchange bias in ferromagnet/antiferromagnet systems.

Findings

Orbital magnetic moment is the main driver of exchange bias.

Pinned moments originate from the orbital component.

Spectroscopy confirms the physical origin of pinned moments.

Abstract

Modern magnetic thin film devices owe their success in large part to effects emerging from interlayer coupling and exchange interaction at interfaces. A prominent example is exchange bias (EB), a magnetic coupling phenomenon found in ferromagnet (F)/antiferromagnet (AF) systems. Uncompensated pinned moments in the AF couple to the F via the interface causing an additional unidirectional anisotropy. As a result, the hysteresis of the F is shifted. The existence of such pinned moments is nowadays accepted although their physical nature and origin is still unknown. Here we present a thorough spectroscopic investigation based on X-ray magnetic circular dichroism which does for the first time provide direct information about the physics of pinned magnetic moments. Our data clearly shows that the orbital magnetic moment, which is usually widely quenched in transition metal systems, is the driving force behind exchange bias in Co/FeMn.