Observation of perpendicular exchange bias in [Pd/Co]-CoO nanostructures: Dependence on size, cooling field, and training

Magnetic [Pd/Co] multilayer structures deposited onto self-assembled particle monolayers were capped with a CoO layer to study the size dependence of perpendicular exchange bias. Compared to the continuous film, the biased caps develop an asymmetric hysteresis loop and show a significantly higher exchange bias field and coercivity strongly depending on the cooling field and number of field cycles. The magnitude of the exchange bias field increases substantially as we scale down the particle diameter. Moreover, in contrast to the film, the coercivity exhibits a nonmonotonic temperature behavior with a local maximum at about 250 K, which may originate from strong spin fluctuations in the antiferromagnet.