Anisotropic compression effects on nanocrystalline crystals of nickel oxide

Nickel oxide (NiO) with bulk crystalline size is an antiferromagnetic insulator correlated strongly with crystal structure. A reduction in crystalline size causes a change in the magnetic sublattice, resulting in the appearance of ferromagnetic moments. Furthermore, in the nano crystals fabricated in mesoporous silica, there is a lattice distortion at the unit cell level that brings about the change in the magnetic property, suggesting a prominent magneto-structural correlation. We investigate anisotropic compression effects on nanocrystalline NiO with a crystalline size (D) of 11.4 nm to observe this remarkable magneto-structural correlation. Magneto-crystalline anisotropy is at its maximum when negative contraction occurs. The negative contraction appears even in a bulk crystal under non-ideal hydrostatic compression, and its anomalous structural change is suppressed with decreasing D.