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

Abstract

We report the annealing-induced exchange bias in Fe–Cu–Pt based heterostructures with Cu as an intermediate layer (Fe/Cu/Pt heterostructure) and as a capping layer (Fe/Pt/Cu heterostructure). The exchange bias (shift in the hysteresis loop along the field axis) 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 °C, while on annealing these heterostructures at 500 and 600 °C a negative exchange bias of ∼ −100 Oe was observed. X-ray and polarized neutron reflectivity measurements show the evolution of the depth-dependent structure and magnetic properties of the heterostructures on annealing at different temperatures and revealed the 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 〉 400 °C resulted into the formation of a ternary alloy phase. The observation of annealing-induced positive and negative exchange bias effect is dependent on the applied field and majority of the magnetic phase (hard/soft), present in the system. This annealing dependent coupling could give rise to more advanced applications of hard/soft ferromagnetic heterostructures.