Induced phase shift in interlayer magnetic exchange coupling: Magnetic layer doping

The changes in the phase of the long-period oscillatory interlayer exchange coupling between two Co layers, separated by a Ru spacer layer, are examined as a function of small concentrations of Ag, Au, Cu, and Ru added to the magnetic Co layer. Phase changes of up to 360 degrees are observed for small concentrations of Ag (up to 8%) with minimal modifications to the coupling period or strength. In addition, an additive antiferromagnetic bias is observed for small interlayer thicknesses, indicative of a superexchange contribution to the interlayer coupling. The effects are also investigated for Cu as the nonmagnetic spacer material and phase shifts are observed similar to those in the systems with Ru as the spacer material. Band-structure calculations are presented that show that insertion of small amounts of Pig into the Co host leads to additional states at the bottom of the band. This lowering of the lower band limit is interpreted as a change in the potential step that determines the spin-dependent reflection coefficients of the electrons crossing the ferromagnet/spacer layer interface. The observed phase shifts are therefore interpreted to directly result from changes in the band structure of the ferromagnetic layer. The insertion of small amounts of nonmagnetic material in the ferromagnetic layer thus provides a mechanism with which the phase of the coupling can be shifted in a well controllable manner.