Superparamagnetic Transition in Diluted Exchange Coupled Bilayers

Abstract

In ferromagnet (FM)/antiferromagnet (AF) bilayer systems, it was recently found that the exchange bias vs. FM thickness curve shows a critical thickness below which the exchange bias vanishes, and confirmed by analytic calculation using a simplified model that it can be ascribed to the superparamagnetism (SPM) promoted through the exchange coupling with the AF layer. This paper studies the effect by means of Monte Carlo simulations and tries to obtain more insight into the phenomenon. The AF layer is randomly diluted up to 0.3 at.% to account for the presence of defects contributing to the exchange bias effect. The influence of the FM dilution on the onset of SPM is investigated.