Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers

TL;DR

This study investigates the exchange bias in NiFe/IrMn bilayers, revealing the dual behavior of uncompensated spins at the interface and the finite size effects on IrMn's anisotropy, using numerical analysis and resonant magnetic reflectometry.

Contribution

It provides new insights into the dual behavior of interfacial uncompensated spins and the finite size effects on IrMn anisotropy in exchange bias systems.

Findings

Uncompensated spins are mainly frozen with minimal rotation.

IrMn anisotropy exhibits a finite size effect.

Interfacial spin disorder is linked to chemical intermixing.

Abstract

We present a comprehensive study of the exchange bias effect in a model system. Through numerical analysis of the exchange bias and coercive fields as a function of the antiferromagnetic layer thickness we deduce the absolute value of the averaged anisotropy constant of the antiferromagnet. We show that the anisotropy of IrMn exhibits a finite size effect as a function of thickness. The interfacial spin disorder involved in the data analysis is further supported by the observation of the dual behavior of the interfacial uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we have observed that the antiferromagnetic uncompensated spins are dominantly frozen with nearly no rotating spins due to the chemical intermixing, which correlates to the inferred mechanism for the exchange bias.