Interlayer coupling in (formula presented) superlattices

Interlayer coupling has been investigated for a series of (Formula presented) (Formula presented) superlattices. The layer of (Formula presented) in the lattices is ferromagnetic for (Formula presented) and causes ferromagnetic coupling between Fe layers for all spacer thicknesses investigated here. As the Si content increases above (Formula presented) the layer becomes nonmagnetic and simultaneously our current in the plane of the sample and current perpendicular to the sample plane measurements suggest that the spacer rapidly changes its conduction property from metallic to highly resistive. Variations of the interlayer magnetic coupling as a function of spacer layer thickness for the spacer compositions above (Formula presented) are similar to each other; namely, with an increase of the spacer thickness the interlayer coupling is initially ferromagnetic, then antiferromagnetic, and finally becomes noncoupling. Moreover, the temperature dependence of the bilinear and biquadratic coupling constants, (Formula presented) and (Formula presented) which were obtained by numerical fitting, varies sensitively with x. Assuming that the conduction of the spacers ranges from metallic to insulating as x increases, all these coupling behaviors can be described qualitatively by the quantum interference model formalized by Bruno. Furthermore, we found that the coupling strength is enhanced dramatically with increase of x of (Formula presented)