Perpendicular Coupling in Exchange-BiasedFe3O4/CoOSuperlattices

The CoO antiferromagnetic ordering in exchange-biased (001) ${\mathrm{Fe}}_3{\mathrm{O}}_4/\mathrm{CoO}$ superlattices has been determined as a function of temperature and magnetic field using neutron diffraction methods. The Co spins preferentially align in domains in which the spins are perpendicular to the net ${\mathrm{Fe}}_3{\mathrm{O}}_4$ moment direction. This 90° orientation between the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and CoO spins is a direct consequence of the interfacial exchange coupling giving rise to exchange biasing, as is not observed in a comparable MgO/CoO superlattice.