Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers

Abstract

Epitaxially grown multilayer systems offer the possibility to study the influence of ferromagnetism on superconductivity in a controlled way. In this paper, we explore how the superconducting properties of high quality epitaxially grown superconductor/normal-metal/ferromagnet trilayers evolve as a function of the exchange splitting in the ferromagnet and the thickness of the normal-metal layer. We report results for Nb(110)/Au(111)/Co(0001) and make a detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use quantitative fast Fourier transform analysis to confirm the existence of a long-period (2.1 nm) oscillation in the superconducting transition temperature ${T}_{\text{c}}$ as a function of the Au-layer thickness ${t}_{\text{Au}}$ for ${t}_{\text{Au}}>2\text{ }\text{nm}$ and highlight an additional short-period (0.76 nm) oscillation for ${t}_{\text{Au}}<3\text{ }\text{nm}$ in Nb/Au/Co. This short-period oscillation can be explained in terms of a damped Ruderman-Kittel-Kasuya-Yoshida-like oscillation of the spin polarization in Au. The robustness of the long-period oscillation against the substitution of Co for Fe suggests that it is intrinsic to the Au(111) layer on Nb and may represent a form of quantum interference in very clean trilayer systems.