Interactions between Ni and NiO

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Abstract
Polycrystalline Ni films, evaporated onto single-crystal NiO substrates, have been studied by torque measurements from 77° to 473°K in fields up to 22 kOe. The NiO films had (111) and (001) orientations, representing planes of parallel and compensated spins, respectively. After short vacuum anneals above TN, the Néel temperature, the major torque symmetry of the films on (001) NiO substrates was sin 4θ with an amplitude that decreased with increasing field. This was due to the rhombohedral distortion of NiO below TN; a (001) crystal consists of twinned, T-domain regions. This oriented strain field in the NiO substrate propagates into the Ni film and produces two orthogonal uniaxial anisotropies by a strain-magnetostriction mechanism. The (111) NiO substrates were also twinned. After annealing above TN, the Ni films on these substrates showed a peak in the rotational hysteresis at ∼1 kOe, and a torque component of sixfold symmetry in the moderate to high-field range. One sample also showed rotational hysteresis that was increasing rapidly at 22 kOe. This behavior is consistent with a model involving exchange anisotropy, the motion of T-domain walls, and a strain-magnetostriction mechanism.

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