Depth resolved study of annealing in IrMn/(Fe, Co, CoFe) exchange bias systems

TL;DR

This study investigates how annealing affects the structural and magnetic profiles of IrMn/(Fe, Co, CoFe) exchange bias systems using advanced scattering and spectrometry techniques, revealing different migration behaviors and their impact on magnetic properties.

Contribution

It provides the first detailed depth-resolved analysis of annealing effects on IrMn-based AFM/FM systems, highlighting migration phenomena and their influence on exchange bias stability.

Findings

Manganese migrates to the surface before annealing, indicating inherent non-homogeneity.

Annealing causes slight manganese migration in CoFe and Co layers without degrading exchange coupling.

Iron migration into the AFM layer during annealing leads to erosion of magnetic profiles and loss of pinning strength.

Abstract

Depth resolved study of structural and magnetic profiles of antiferromagnetic/ferromagnetic (AFM/FM) system upon annealing was performed in this work. We studied systems comprising of AFM IrMn and FM (Co, Fe, Co$_{70}$Fe$_{30}$) structures using polarized neutron and soft X-ray scattering, secondary neutral spectrometry, and magnetometry. Structural depth profiles obtained from neutron reflectometry indicate non-homogeneity of the AFM layer even before annealing, which is associated with the migration of manganese to the surface of the sample. Annealing of samples with CoFe and Co layers leads to a slight increase ($\sim$ 5 %) in the migration of manganese, which, however, does not lead to significant degradation of the exchange coupling at the AFM/FM interface. A significantly different picture was observed in the Fe/IrMn systems where a strong migration of iron into the AFM layer was observed upon annealing of the sample, leading to erosion of the magnetic profile, the formation of a non-magnetic alloy and degradation of the pinning strength. This study can be useful in the design of AF/FM systems in different spintronics devices, including HDD read heads, where thermal annealing is applied at different stages of the device manufacturing process.