Exchange Bias and Blocking Temperature Distribution of Fe-Film/CoO-Nanoparticle Hybrid Bilayers

We fabricated and characterized Fe-film/CoO-nanoparticle hybrid bilayers and studied their temperaturedependent magnetic properties. The magnetic nanoparticles are uncoupled or weakly coupled in the particle films, which essentially resemble the antiferromagnetic grains in the deposited thin films. The size and size distribution of the nanoparticles can be well-controlled by chemical synthesis prior to assembling, providing additional route for engineering the antiferromagnetic layer in exchange-bias systems. Using cycled annealing-cooling measurements, we observed a unimodal blocking-temperature distribution in our samples that is a reflection of the intrinsic antiferromagnetic monodisperse “grain” size distribution. The absence of the low-temperature contribution is likely attributed to both the fabrication process and the nanoparticle morphology.