Decoupling of superconducting V by ultrathin Fe layers in V/Fe multilayers

Abstract

We report on a detailed study of superconducting critical temperatures ${\mathit{T}}_{\mathit{c}}$ and critical fields ${\mathit{H}}_{\mathit{c}2}$ of V/Fe multilayers. The thickness of the V layers (${\mathit{d}}_{\mathrm{V}}$) and Fe layers (${\mathit{d}}_{\mathrm{Fe}}$) as well as the total number of layers in the multilayer (N) were varied systematically. For ${\mathit{d}}_{\mathrm{Fe}}$≥0.6 nm, at constant ${\mathit{d}}_{\mathrm{V}}$, ${\mathit{T}}_{\mathit{c}}$ and the critical fields for parallel (${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$) and perpendicular (${\mathit{H}}_{\mathit{c}2\mathrm{\perp }}$) orientation do not depend on either ${\mathit{d}}_{\mathrm{Fe}}$ or N, and a two-dimensional (2D) temperature dependence for ${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$ without 3D-2D crossover is observed for small values of ${\mathit{d}}_{\mathrm{V}}$. The predicted oscillatory behavior of ${\mathit{T}}_{\mathit{c}}$ as a function of ${\mathit{d}}_{\mathrm{Fe}}$ is not found. We conclude that the superconducting V layers are completely decoupled by only 0.6 nm Fe, in conflict with previous reports. Upon decreasing ${\mathit{d}}_{\mathrm{V}}$ at constant ${\mathit{d}}_{\mathrm{Fe}}$, a strong decrease of ${\mathit{T}}_{\mathit{c}}$ is found. This, together with the temperature dependence of ${\mathit{H}}_{\mathit{c}2\mathrm{\parallel }}$ and ${\mathit{H}}_{\mathit{c}2\mathrm{\perp }}$ for all samples can be described by existing theory.