Mössbauer investigation of the growth of the Fe multilayer in Fe(100)/Ag(100) structures

A monolayer of ⁵⁷Fe is used as a probe layer in molecular-beam-epitaxy-grown Ag/Fe(001)/Ag(001) structures. Different Fe sites can be distinguished in the iron multilayer based on the isomer-shift (i.s.) and quadrupole-splitting (QS) values of different components in the M\"ossbauer spectrum. This makes it possible to determine the concentration of ⁵⁷Fe atoms in the different atomic Fe layers and obtain information about the growth processes for different regions of the Fe multilayer. It was found that after deposition of about 5-Fe ML the growth changes from a Fe multilayer formation mode to a quasi-layer-by-layer mode. The values of the i.s. and QS are the same for Fe atoms located at the top and bottom Ag/Fe interface. Hhf values, on the other hand, are different by 9 kOe at the top and bottom for a sample in which the upper Ag(001) layer is covered by another Fe(001) layer. This result may be due to a contribution to the top Hhf value from Ruderman-Kittel-Kasuya-Yosida-like spin-density oscillations that couple the ferromagnetic Fe multilayers across the nonmagnetic Ag spacer.