Annealing driven positive and negative exchange bias in Fe-Cu-Pt heterostructures at room temperature

TL;DR

This study demonstrates how annealing temperature influences positive and negative exchange bias in Fe-Cu-Pt heterostructures at room temperature, revealing complex interfacial magnetic interactions and phase evolution.

Contribution

It uncovers the temperature-dependent switch between positive and negative exchange bias in Fe-Cu-Pt heterostructures and links it to interdiffusion and phase formation at interfaces.

Findings

Positive exchange bias of 120 Oe at 400°C

Negative exchange bias of ~ -100 Oe at 500°C and 600°C

Interdiffusion leads to ternary alloy formation and complex magnetic phases

Abstract

We report annealing induced exchange bias in Fe-Cu-Pt based heterostructures with Cu as an intermediate layer (Fe/Cu/Pt heterostructure) and capping layer (Fe/Pt/Cu heterostructure). Exchange bias observed at room temperature (300 K) is found to be dependent on the annealing temperature. We obtained positive exchange bias of 120 Oe on annealing both the heterostructures at 400 oC, while on annealing these heterostructures at 500 and 600 oC a negative exchange bias of ~ -100 Oe was found. X-ray reflectivity and polarized neutron reflectivity measurements provided evolution of depth dependent structure and magnetic properties of the heterostructures on annealing at different temperatures and revealed coexistence of soft and hard (alloy) magnetic phases across the thickness of the films. Rapid and long range interdiffusion at interfaces on annealing the systems at a temperature above 400 oC resulted into formation of a ternary alloy phase. These results can be understood within the context of a very unusual interface exchange interaction at the interface of hard/soft magnetic phases, which are dependent on the annealing temperature.