Compositional control of the interlayer exchange coupling in magnetic multilayer structures

The interlayer magnetic coupling in two different high quality MBE grown trilayer systems, Co/Ru/Co and Co/Cu/Co, has been systematically studied. A strong anti-parallel superexchange bias at low Ru thickness in the Ru spacer systems has been observed, which is expected for Ru spacer since Ru has a large local density states above the Fermi level.; The effect of adding small amounts of Ag to the Co layers in the two different spacer systems has also been investigated. Small shifts in the average potential, measured relative to the Fermi level, are expected upon doping the magnetic films with small amounts of another metal. Ag was chosen because it is immiscible in the Co and forms very small clusters ({dollar}<{dollar}10 A). This leads to a maximum amount of possible charge transfer with a minimum perturbation of the Co band structure. A shift of 0.4 eV in the Fermi level has been calculated for a Ag concentration of 12.5% in Co. This will change the average potential seen by the 's' and 'd' electrons in the Co layers and thereby affect the RKKY coupling. A change in the potential directly influences the reflection coefficients of electrons at the Co/spacer interfaces and so the effects should appear primarily as shifts in the phase of the oscillations as a function of spacer film thickness. In the experiments, it was found that the phases changed up to 360{dollar}spcirc{dollar} for the Ru spacer systems and 120{dollar}spcirc{dollar} for the Cu spacer systems for Ag concentration up to 8%. However, the period or amplitude of the coupling was not affected significantly.; In addition, a dependence of the interlayer exchange coupling on the magnetic layer thickness has been observed in asymmetric Co(32 A)/Ru{dollar}(tsb{lcub}Ru{rcub}){dollar}/Co{dollar}(tsb2){dollar} trilayer systems within which {dollar}tsb{lcub}Ru{rcub}{dollar} is a constant. As a function of the second Co layer thickness, the amplitude of the coupling constant, {dollar}Asb{lcub}12{rcub},{dollar} varies significantly but the sign of {dollar}Asb{lcub}12{rcub}{dollar} does not change within each series. In both parallel and anti-parallel coupled structures, the variation length {dollar}Delta tsb2{dollar} between the maximum and the minimum coupling strength is about 10 A and consistent from series to series.