THEORY OF NON-HEISENBERG EXCHANGE - RESULTS FOR LOCALIZED AND ITINERANT MAGNETS

A general formulation of intersite (layer) exchange coupling in bulk ( multilayer) materials is proposed based on the treatment of the spin ( layer) rotation as a perturbation in terms of the force theorem and mu ltiple scattering theory. The expansion of the intersite (layer) excha nge interaction energy gives expressions for the bilinear and biquadra tic exchange. For metals, the approach is illustrated by linear muffin -tin orbital calculations of exchange coupling constants in the ferrom agnetic 3D-metals and the fee phase of bulk Fe. Long range oscillation s of strongly volume dependent exchange coupling in fee Fe appears to be the origin of the spin-density-wave instability in this metastable phase. The correctness of expressions for the limit of localized magne ts is demonstrated by calculations for the antiferromagnetic insulator NiO. In contrast with other theories, this method can be used for bot h nonmagnetic and magnetic spacers in metallic multilayers, as is illu strated by calculations of the interfacial and interlayer exchange in Fe/Mn and Co/Mn. (C) 1996 American Institute of Physics.