Indirect magnetic interaction through silver in epitaxial Fe(110)/Ag(111) multilayers

Evidence for an indirect magnetic interaction through silver has been observed in three different series of high-quality monocrystalline Fe(110)/Ag(111) multilayer films fabricated by molecular-beam epitaxy. These multilayers consisted of 3-, 5-, or 8-monolayer (ML) bilayer components of Fe; each respective series had Ag bilayer components ranging from 4 to 20 ML’s. An analysis of the temperature dependence of magnetization (as determined by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy) indicated that there was a magnetic coupling between neighboring Fe bilayer components through the intervening Ag. This interlayer coupling could be seen through variations in the ${\mathit{T}}^{3/2}$ dependence of the hyperfine field in the 5- and 8-ML Fe component multilayers. However, the 3-ML Fe component series exhibited a linear T to ${\mathit{T}}^{3/2}$ dimensional crossover in the hyperfine-field temperature dependence. Specifically, the linear temperature dependence of the 3-ML film with a thick Ag component (the magnetically uncoupled case) represented the behavior of a genuine two-dimensional ferromagnet. However, as the interlayer magnetic coupling increased with decreasing Ag thickness, a temperature dependence (at low temperatures) developed that increasingly resembled that of three-dimensional ferromagnetism, i.e., a ${\mathit{T}}^{3/2}$ law.