Perpendicular magnetization in CoO (111) layers induced by exchange interaction with ferromagnetic Co and Ni60Cu40 nanoclusters

The magnetization reversal of ferromagnetic nanoparticles coupled by exchange with a CoO (111) thin film has been studied. The interfacial exchange interaction triggers the appearance of an out-of-plane magnetization in the CoO (111) film. Co and Ni60Cu40 particles were chosen, as they present an order of magnitude difference in the saturation magnetization and Curie temperatures that surround the Néel temperature of CoO. In both cases, the exchange coupling leads to an increase of the coercive field, up to 200% in Co particles, and small exchange bias of 100 Oe when the external magnetic field is applied in the CoO (111) plane. When the field is applied along the CoO [111] direction, an unexpected net magnetization of the CoO (111) layer is revealed. Interestingly, it scales with the particles magnetization. The results are explained in terms of a large interfacial interaction and an induced canting of the CoO spins in the close region of the interface. The large value of the CoO magnetization indicates that the canting settles over an extended thickness of at least 3.7 nm and 1.2 nm in the cases of Co and Ni60Cu40 particles, respectively, which is consistent with a compensated antiferromagnetic spins surface.