INTERLAYER EXCHANGE COUPLING IN FE CR MULTILAYERS/

We investigate the origin of the long-period oscillation of the interl ayer exchange coupling in Fe/Cr trilayer systems. Within the stationar y phase approximation the periods of the oscillations are associated w ith extremal vectors of the Fermi sphere of Cr. Using a realistic tigh t-binding model with spin-orbit interaction we calculate the coupling strength for each extremal vector based on the spin asymmetry of the r eflection amplitude for a propagating state impinging from the Cr to F e layer. We find that for the (001) and (110) growth directions the bi ggest coupling strength comes from the extremal vector centered at the ellipsoid N of the Fermi surface of Cr.