In order to understand the interplay between exchange coupling and magnetic
structure, we have examined the magnetic ordering of a series of epitaxial
Fe3O4/NiO superlattices using polarized neutron diffraction techniques. As
expected, the net ferrimagnetic moment of the Fe3O4 layers aligns parallel
to an applied magnetic field. The antiferromagnetic NiO spins order into a
lternating antiparallel [111] planes as in bulk, but the direction of the s
pins in the planes are determined by field preparation. The NiO moments ten
d to align perpendicular to the field. In addition, the relative population
of the NiO domains varies as the field is raised. The changes in the antif
erromagnetic spin order relative to bulk seem to result from magnetic coupl
ing with the Fe3O4 moments. (C) 1999 American Institute of Physics. [S0021-
8979(99)67708-8].