We show that antiferromagnetic nanoparticles of alpha-Fe2O3 (hematite) under wet conditions can attach into chains along a common  axis. Electron microscopy shows that such chains typically consist of two to five particles. X-ray and neutron diffraction studies show that both structural and magnetic correlations exist across the interfaces along the  direction. This gives direct evidence for exchange coupling between particles. Exchange coupling between nanoparticles can suppress superparamagnetic relaxation and it may play a role for attachment along preferred directions. The relations between exchange coupling, magnetic properties, and oriented attachment are discussed.
Physical Review B (condensed Matter and Materials Physics), 2005, Vol 72, Issue 21