Oscillatory Exchange Bias Controlled by RKKY in Magnetic Multilayers

TL;DR

This paper demonstrates how RKKY-mediated exchange interactions in magnetic multilayers can be used to control and modulate the exchange bias strength, achieving significant tunability through spacer thickness variations.

Contribution

It introduces a novel method of controlling exchange bias via RKKY oscillations in multilayer structures, combining direct and indirect exchange effects.

Findings

Exchange bias strength oscillates with N-spacer thickness.

Modulation of bias reaches up to 400% at RKKY peak.

Superposition of direct and indirect exchange explains the effect.

Abstract

Ferromagnetic/antiferromagnetic bilayers are interfaced with normal metal/ferromagnetic bilayers to form F*/AF/N/F valves. The N-spacer thickness is chosen such that it mediates strong indirect exchange (RKKY) between the outer magnetic layers, which varies in strength/direction depending on the N thickness and in direction on switching F. The system exhibits a strong modulation of the F*/AF exchange bias, oscillating in strength syncronously with the oscillation in the interlayer RKKY exchange across the normal metal spacer. The effect is explained as due to a superposition taking place within the antiferromagnetic layer of the direct-exchange proximity effect from the F*/AF interface and the indirect RKKY exchange from F penetrating AF via N. The modulation, expressed via the strength of the F*/AF bias field, reaches 400% at the first RKKY peak.