Oscillatory ferromagnetic interlayer coupling of Fe(110) thin films through (111) oriented Ag and Cu spacers

The magnetic coupling of Fe(110) thin films through epitaxial (111) oriented noble-metal spacers has been investigated using a site-specific Mossbauer spectroscopy technique that is sensitive to changes in the interfacial Fe spin-wave spectrum. As the interlayer exchange oscillates, the interfacial spin-wave modes are alternately softened and stiffened. To qualitatively connect the observed spin-wave behavior to the effective exchange al the Fe/noble-metal interface, the system is modeled using two semi-infinite simple cubic ferromagnets which may interact either ferromagnetically or antiferromagnetically. Vibrating-sample magnetometry and superconducting quantum interference device magnetometry measurements determined that the interlayer coupling is always ferromagnetic. As the interlayer thickness is increased, the spin-wave behavior indicates an oscillatory component superimposed on a monotonic decrease in the ferromagnetic exchange coupling. The periodicities of the oscillatory component are 6 monolayers (ML)) for Ag(111) and 4.5 ML for Cu(111), in close agreement with the expected periodicities from the bulk Fermi-surface spanning vectors.