Superparamagnetic Transition in Diluted Exchange Coupled Bilayers

摘要

In our previous work[1-2] we found, in ferromagnet (FM)/antiferromagnet (AF) bilayer systems, 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)[3-4] promoted through the exchange coupling with the AF layer. This paper studies the effect by means of Monte Carlo simulations[2] and tries to obtain more insight into the phenomenon. The AF layer is randomly diluted up to 0.3at.% 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.