Antiferromagnetic NiO nanoparticles exhibit anomalous magnetic propert
ies, such as large moments, and coercivities and loop shifts of up to
10 kOe. This behavior is difficult to understand in terms of 2-sublatt
ice antiferromagnetic ordering which is accepted for bulk NiO. Numeric
al modeling of spin configurations in these nanoparticles yields 8-, 6
-, or 4-sublattice configurations, indicating a new finite size effect
, in which the reduced coordination of surface spins causes a fundamen
tal change in the magnetic order throughout the particle. The relative
ly weak coupling between the sublattices allows a variety of reversal
paths for the spins upon cycling the applied field, resulting in large
coercivities and loop shifts.