LATTICE MISFIT STRAIN AS ORIGIN FOR BIQUADRATIC INTERLAYER COUPLING

The direct observations of some MBE grown superlattices show large int erfacial undulations, which is attributed to the elastic relaxation of tensile layers. Assuming that the interface lateral lattice deformati on, due to ionic radii misfit, is given by the periodic solution of th e Frenkel-Kontorova model, we calculate the magnetoelastic contributio n to the biquadratic magnetic coupling between ferromagnetic layers ac ross the nonmagnetic spacer. We show that due to the correlated modula tions of the effective bilinear exchange integral, there arises a biqu adratic exchange which favours perpendicular orientations of magnetiza tion in adjacent ferromagnetic layers.