The interactions between Ni and NiO were investigated by examining the magnetic properties of Ni films on single-crystal NiO substrates. The orientations of the NiO substrates were (001) (compensated spin planes), and (111) (parallel spin planes). With (001) NiO the Ni films were strained an amount corresponding approximately to the rhombohedral deformation of NiO below its Néel temperature. The amplitude and symmetry of magnetic torque data were consistent with the magnitude of this strain and the symmetry of the antiferromagnetic domain structure, respectively. Ni films on (111) NiO substrates had a complex field dependence of rotational hysteresis. This behavior was analyzed in terms of exchange anisotropy coupling and the interaction of the field with both the Ni and NiO spin systems. The analysis provided good agreement with the data for an exchange anisotropy energy of 1.75 erg/cm2 of interface, a crystalline anisotropy of NiO in its parallel spin plane of 1.1×103 erg/cc NiO, and a "flop field" for NiO in its parallel spin plane of 5 to 10 kOe. The analysis showed that two new regions of rotational hysteresis loss are present in fields ≥ the "flop field" of the antiferromagnetic spin system. Some more general features of exchange anisotropy coupling are also discussed. © 1965 The American Institute of Physics.