Isolation of proximity-induced triplet pairing channel in a superconductor/ferromagnet spin valve

Andrey Kamashev,Joachim Schumann,Jürgen Thomas,Aidar Validov,Bernd Büchner,Yakov Fominov,Vladislav Kataev,Nadir Garif’Yanov,Pavel Leksin,Ilgiz Garifullin,N Perov,A Semisalova

doi:10.1051/epjconf/201818508001

Andrey Kamashev, Joachim Schumann + Show 10 more

Open Access

https://doi.org/10.1051/epjconf/201818508001

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Abstract

In the present work we have studied the proximity-induced superconducting triplet pairing in CoOx/Py1/Cu/Py2/Cu/Pb spin-valve structure (where Py = Ni0:81Fe0:19). For CoOx(3 nm)/Py(3 nm)/Cu(4 nm)/Py(0.6 nm)/Cu(2 nm)/Pb(70 nm) we have studied the dependence of the Tc on the angle α between the direction of the cooling field and the external field both applied in the plane of the sample. We obtained that the Tc does not change monotonically with the angle but passes through a minimum. To observe an “isolated” triplet spin-valve effect we exploited the oscillatory feature of the magnitude of the ordinary spin-valve effect ΔTc in the dependence of the Py2-layer thickness dPy2. We determined the value of dPy2 at which ΔTc caused by the ordinary spin-valve effect is suppressed. This means that the difference in the Tc between the antiparallel and parallel mutual orientation of magnetizations of the Py1 and Py2 layers is zero. For such a sample a “pure” triplet spin-valve effect which causes the minimum in Tc at the orthogonal configuration of magnetizations has been observed.

Highlights

We analyzed the dependence of the superconducting transition temperature Tc on the angle α between the magnetizations of the Py1 and Py2 ferromagnetic layers in the magnetic field H0 = +100 Oe applied in the plane of the sample
This difference in magnitude of the spin-valve effect ∆Tc is associated with the fact that, for the thickness of the permalloy layer dPy2 = 3 nm in sample 2, the wave function of superconductor Cooper pairs almost completely decays in the Py2 ferromagnetic layer
Py1 has little influence on the superconductivity and, on the magnitude of the superconducting spinvalve effect ∆Tc. This is consistent with the fact that, in accordance with the theory, a decrease in the thickness of the permalloy layer dPy2 leads to an increase in the superconducting spin-valve effect ∆Tc

Summary

Introduction

The optimal thickness of the Pb layer dPb = 70 nm was determined from the Tc(dPb) curve measured at a constant dPy1 = 5 nm, which is much larger than the penetration depth ξh of Cooper pairs into ferromagnetic Py. Basing on our data on Tc(dPy) at fixed dPb we estimate this value as ξh∼1.1 nm. Earlier we revealed that the F1-layer thickness at a fixed dF2 does not significantly influence ∆Tc for the sample set CoOx(2.5 nm)/Fe1(dFe1)/Cu(4 nm)/Fe2(dFe2)/Cu(1.2 nm)/Pb(60 nm) and that a thin Cu(1.2 nm) interlayer between F2- and S- layers is completely transparent for the Cooper pairs [17]

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Conclusion