Proximity effect in [Nb(1.5 nm)/Fe(x)]10/Nb(50 nm) superconductor/ferromagnet heterostructures.

Yury Khaydukov,Thomas Keller,Roman Morari,Laura Guasco,Gideok Kim,Sabine Pütter,Bernhard Keimer,Anatolie Sidorenko

doi:10.3762/bjnano.11.109

Abstract

We have investigated the structural, magnetic and superconduction properties of [Nb(1.5 nm)/Fe(x)]10 superlattices deposited on a thick Nb(50 nm) layer. Our investigation showed that the Nb(50 nm) layer grows epitaxially at 800 °C on the Al2O3(1−102) substrate. Samples grown at this condition possess a high residual resistivity ratio of 15–20. By using neutron reflectometry we show that Fe/Nb superlattices with x < 4 nm form a depth-modulated FeNb alloy with concentration of iron varying between 60% and 90%. This alloy has weak ferromagnetic properties. The proximity of this weak ferromagnetic layer to a thick superconductor leads to an intermediate phase that is characterized by a suppressed but still finite resistance of structure in a temperature interval of about 1 K below the superconducting transition of thick Nb. By increasing the thickness of the Fe layer to x = 4 nm the intermediate phase disappears. We attribute the intermediate state to proximity induced non-homogeneous superconductivity in the structure.

Highlights

Superconductor(S)/ferromagnet(F) heterostructures are intensively studied systems, which are interesting for fundamental physics due to a big number of predicted and detected phenomena such as the appearance of non-uniform superconducting states
One possible way to exert such a control is via interaction of superconductivity and interlayer exchange coupling (IEC) of F layers through a normal metal (NM) spacer
The interaction of exchange coupling can be studied by integral magnetometric methods such as SQUID magnetometry [30] or depth-resolved techniques such as polarized neutron reflectometry (PNR) [31]

Summary

Introduction

Superconductor(S)/ferromagnet(F) heterostructures are intensively studied systems, which are interesting for fundamental physics due to a big number of predicted and detected phenomena such as the appearance of non-uniform superconducting states (see reviews [1,2,3]). Among these phenomena are π–Josephson junctions [4,5,6,7] with a π-phase difference of super-. The interaction of exchange coupling can be studied by integral magnetometric methods such as SQUID magnetometry [30] or depth-resolved techniques such as polarized neutron reflectometry (PNR) [31]

Objectives

Results

Discussion

Conclusion