Role of the antiferromagnet in exchange-biased Fe3O4/CoO superlattices

Using neutron diffraction techniques, we have directly characterized the antiferromagnetic spin structure of CoO in exchange-biased Fe3O4/CoO (001) superlattices. The CoO antiferromagnetic order is long-range and extends coherently across intervening ferrimagnetic Fe3O4 layers. The ordering is influenced significantly by not only epitaxial growth constraints but also by couplings to the Fe3O4 layers. The antiferromagnetic order in these Fe3O4/CoO (001) samples exhibits significant dependence on field cooling preparations. The CoO spins show a strong tendency to align perpendicular to the net ferrimagnetic moment with some changes in the average domain size associated with field cooling. The CoO spin structure in the exchange-biased state illustrates important aspects of recent biasing theories but with unusually large domain sizes. (C) 1998 American Institute of Physics. [S0021-8979(98)17811-8].