Exchange bias and coercivity in oxygen-exposed cobalt clusters

Abstract

Exchange bias and coercivity have been studied in nanometric-size cobalt clusters as a function of oxygen exposure under high vacuum. This technique allows looking at the early stages of oxidation, as well as studying exchange bias in small clusters before they are completely transformed into oxide. It is found that oxygen induces at first an increase in the coercive field and in the superparamagnetic blocking temperature, before any substantial loss in the magnetization, which indicates that this effect is due to adsorbed oxygen rather than to exchange coupling with an oxide overlayer.