Exchange bias in a Co/CoO/Co trilayer with two different ferromagnetic-antiferromagnetic interfaces

The exchange-bias properties of a Co/CoO/Co sandwich structure are examined. The Co/CoO bottom bilayer was obtained by oxidation of a Co layer and the top bilayer was formed by subsequent deposition of Co on top of CoO. The strength of the interfacial coupling is shown to be stronger at the bottom Co/CoO interface than at the top interface. A number of original properties characterize exchange bias of the top bilayer. This includes weak temperature dependence of the bias field, weak coercivity due to exchange bias, and lack of the training effect. These properties suggest that the antiferromagnetic moment configuration is frozen during magnetization reversal of the top Co layer.