Bilinear and biquadratic interlayer exchange coupling in ferromagnet-nonmagnetic metal multilayer film

The model of biquadratic exchange coupling is extended by taking into account the demagnetizing, anisotropy fields and nonlocal interlayer bilinear exchange coupling. Biquadratic exchange coupling constant B₁₂ absolute value reduces due to finite correlation length of the magnetization fluctuations. The cases when the fluctuation contribution to energy density is not reduced to the biquadratic form are considered. B₁₂ reveals a likely magnetic anisotropy at film magnetizing if ferromagnetic layer thickness is sufficiently small. The experiments on multilayer Co/X (X is nonmagnetic metal) films are discussed