Results of analysis of magnetic states of a ferromagnetic system, which can be used when interpreting hysteresis properties of multilayer ferromagnetic films with antiferromagnetic interaction between the layers, are given. In the model of uniform rotation of magnetization vectors magnetic phase diagrams were calculated and stability ranges of different magnetic states of monoaxial ferromagnetic crystals, containing antiferromagnetic defects, were determined. Anisotropy of hysteresis loops, coercive force and relative residual magnetization of the crystal at different densities of the antiferromagnetic defects were investigated.