On the relationship between perpendicular coupling and exchange biasing...

In studying well-characterized, exchange-biased Fe3 O4 /CoO superlattices, we show that a causal link exists between the exchange bias phenomenon and the perpendicular coupling of the ferrimag- netic and antiferromagnetic spins. Neutron diffraction studies reveal that for thin CoO layers, the onset temperature for exchange biasing TB matches the onset of locked-in, preferential perpendic- ular coupling of the spins, rather than the antiferromagnetic ordering temperature TN . The results are explained by considering the role of anisotropic exchange first proposed by Dzyaloshinsky and Moriya and developing a model based purely on information on structural defects and exchange for transition metal oxides. The devised mechanism provides a general explanation of biasing in systems with perpendicular coupling.