Microwave surface impedance of proximity-coupled superconducting (Nb) / spin-glass (CuMn) bilayers

TL;DR

This study measures the surface impedance of Nb/CuMn bilayers at 10 GHz to explore the magnetic effects on superconducting proximity, revealing behavior distinct from normal metals and modeled by two electrodynamic theories.

Contribution

It provides experimental data on superconducting/spin-glass bilayers and compares two models describing their electrodynamics, highlighting magnetic influence.

Findings

CuMn acts as a weak ferromagnet affecting superconductivity.

Surface impedance differs significantly from superconductor/normal-metal systems.

Proximity-coupling length scale remains temperature independent.

Abstract

The surface impedance of Nb/CuMn (superconducting/spin-glass) bilayers has been measured at 10 GHz with the parallel plate resonator technique to obtain information about the exotic behavior of the order parameter in superconducting/magnetic proximity systems. The data strongly differs from the superconducting/normal-metal case, showing the magnetic nature of the CuMn layer, which acts as a weak ferromagnet. The results are described in the framework of two models for the electrodynamics of superconducting/ferromagnetic (S/M) bilayers characterized by a proximity-coupling length scale which is independent of temperature.