Observation of the Triplet Spin-Valve Effect in a Superconductor-Ferromagnet Heterostructure

TL;DR

This paper reports the experimental observation of the triplet spin-valve effect in a superconductor-ferromagnet heterostructure, demonstrating how non-collinear magnetization alignment suppresses superconductivity due to triplet pairing.

Contribution

It provides experimental evidence of long-range triplet pairing in S-F heterostructures with non-collinear magnetizations, confirming theoretical predictions.

Findings

Superconductivity is suppressed at non-collinear magnetization alignment.

The resistance measurements show a lower Tc at NCA compared to collinear states.

Triplet pairing generation affects the superconducting transition temperature.

Abstract

The theory of superconductor-ferromagnet (S-F) heterostructures with two ferromagnetic layers predicts the generation of a long-range, odd-in-frequency triplet pairing at non-collinear alignment (NCA) of the magnetizations of the F-layers. This triplet pairing has been detected in a Nb/Cu41Ni59/nc-Nb/Co/CoOx spin-valve type proximity effect heterostructure, in which a very thin Nb film between the F-layers serves as a normal conducting (nc) spacer. The resistance of the sample as a function of an external magnetic field shows that for not too high fields the system is superconducting at a collinear alignment of the Cu41Ni59 and Co layer magnetic moments, but switches to the normal conducting state at a NCA configuration. This indicates that the superconducting transition temperature Tc for NCA is lower than the fixed measuring temperature. The existence of a minimum Tc, at the NCA regime below that one for parallel or antiparallel alignments of the F-layer magnetic moments, is consistent with the theoretical prediction of a singlet superconductivity suppression by the long-range triplet pairing generation.