Experimental and theoretical analysis of the upper critical field in FSF trilayers

TL;DR

This study combines experimental measurements and quasiclassical theory to analyze the upper critical magnetic field in FSF trilayers, revealing a transition from oscillatory to reentrant behavior influenced by external magnetic fields.

Contribution

It introduces a comprehensive theoretical model that accurately predicts the critical field behavior in FSF trilayers, validated by experimental data across various sample configurations.

Findings

Observation of transition from oscillatory to reentrant Tc behavior

Good agreement between theory and experiment using a single set of parameters

Confirmation of FFLO physics relevance in CuNi/Nb/CuNi trilayers

Abstract

The upper critical magnetic field H_{c2} in thin-film FSF trilayer spin-valve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable thicknesses of the bottom and of the top Cu_{41}Ni_{59} F-layers are prepared in a single run, utilizing a wedge deposition technique. The critical field H_{c2} is measured in the temperature range $0.4-8$ K and for magnetic fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of the superconducting transition temperature versus F-layers thickness, induced by an external magnetic field, has been observed for the first time. In order to properly interpret the experimental data, we develop a quasiclassical theory, enabling one to evaluate the temperature dependence of the critical field and the superconducting transition temperature for an arbitrary set of the system parameters. A fairly good agreement between our experimental data and theoretical predictions is demonstrated for all samples, using a single set of fit parameters. This confirms adequacy of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual superconducting properties of the studied Cu_{41}Ni_{59}/Nb/Cu_{41}Ni_{59} spin-valve core trilayers.