MOSSBAUER STUDIES OF SPIN-WAVE EXCITATIONS IN FE/AG MULTILAYERS

The magnetic properties of molecular beam epitaxially (MBE) grown Fe(110)/Ag(111) heterostructures were investigated with Mossbauer spectroscopy. The Fe bilayers were fixed at 3 ML (monolayer) thickness and the Ag bilayer thickness varied from 4 ML to 20 ML. We found that as the Ag layer became thick enough (> 17 ML) to magnetically isolate the Fe layers, a quasi-linear temperature dependence of the hyperfine field results due to the 2-D spin wave excitations. As the Ag layer is reduced, a dimensional crossover in the excitations is induced by the magnetic interaction between Fe layers which makes M(T) change from a two-dimensional T relation to a three-dimensional T3/2 dependence. We constructed a simple theoretical model to motivate the explanation for the experimental results and obtained approximate values for the interlayer coupling strength for various Ag bilayer thicknesses.