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

Using neutron diffraction techniques, we have directly characterized the an tiferromagnetic spin structure of CoO in exchange-biased Fe3O4/CoO (001) su perlattices. The CoO antiferromagnetic order is long-range and extends cohe rently across intervening ferrimagnetic Fe3O4 layers. The ordering is influ enced significantly by not only epitaxial growth constraints but also by co uplings to the Fe3O4 layers. The antiferromagnetic order in these Fe3O4/CoO (001) samples exhibits significant dependence on field cooling preparation s. The CoO spins show a strong tendency to align perpendicular to the net f errimagnetic moment with some changes in the average domain size associated with field cooling. The CoO spin structure in the exchange-biased state il lustrates important aspects of recent biasing theories but with unusually l arge domain sizes. (C) 1998 American Institute of Physics. [S0021-8979(98)1 7811-8].