THE LOCK-IN AND REORIENTATIONAL PHASE-TRANSITIONS IN METALLIC SUPERLATTICES

We show that in the metallic magnetic superlattices, along with the bi linear RKKY-like exchange, there is significant biquadratic contributi on arising from intrinsic and fluctuational mechanisms. Within the phe nomenological approach, we postulate a particular form of free energy density functional and study the thermodynamic behaviour of the system under consideration. The model permits a transparent interpretation o f the phase transitions, observed in metallic multilayers, with multip le oscillation periods and biquadratic exchange effects taken into acc ount.