Asymmetric superconducting spin valves based on the Fe/V layer system grown on MgO(100)

Abstract

We studied asymmetric superconducting spin valves with the layer sequence V/Fe/V/Fe/CoO, grown on MgO(100). These thin film heterostructures exhibit a superconducting spin valve (SSV) effect, that is, a difference, T s , between the superconducting transition temperatures T s with the magnetization directions of the two Fe layers oriented antiparallel and parallel. For pure Fe layers in the SSV we observe a maximum shift T s = 24 mK. On replacing the Fe layers with FeV alloy layers, the SSV effect was increased to a maximum value of T s = 35 mK. This is one of the largest shifts observed in SSV devices up to now, but still an order of magnitude smaller than the SSV effect observed in V layers grown on epitaxial Fe/V superlattices previously. Our results suggest a dominant importance of the Fe/V interface quality for the amplitude of the SSV effect.

Superconducting spin-valve effect and triplet superconductivity inCoOx/Fe1/Cu/Fe2/Cu/Pbmultilayer

“…Structures similar to suggested by Oh et al [1] were investigated to a less extent. A studied [Fe/V] n antiferromagnetically coupled superlattice with thick superconducting vanadium layer on the top instead of a single F1/N/F2 trilayer [22][23][24] was not actually the spin valve device because the system could not be switched from the AP to P orientation of the magnetizations instantaneously. At the same time the analysis of the temperature dependence of the critical field has shown that implicitly ∆T c of this structure can reach up to 200 mK at δT c ∼100 mK.…”

Large Superconducting Spin Valve Effect and Ultrasmall Exchange Splitting in Epitaxial Rare-Earth-Niobium Trilayers

“…Despite the ultra-small E ex in comparison even with weak TM ferromagnets, we see a very large reversible ∆T c0 ≈ 400 mK which is in quantitative agreement with the theoretical model. Previous theories suggested that to get a sizable ∆T c0 it is crucial to have a high interface transparency, a small pair-breaking scattering, and a large superconducting coherence length because Cooper pairs have to sense the exchange field from both F layers [8,10,19]. The fully epitaxial nature of our SSVs should improve interface quality and hence provide a reasonably high interface transparency and a small interface scattering as evidenced by the small dimensionless interfacial resistance γ b ~ 0.3.…”

“…The superconducting spin valve (SSV) exploits proximity-coupling between a superconductor and two ferromagnet (F) layers such that the exchange-induced suppression of the critical temperature (T c ) is controlled by the relative magnetization orientation of the F layers [2-5]. To date, experimental realization of this effect [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] has been limited to transition metal (TM) F layers and the maximum ∆T c between parallel (P) and antiparallel (AP) orientation is about 40 mK, with a T c below 0.4 K [9]. Although ∆T c was improved to 200 mK with a T c around 2.8 K, this was obtained in a large (kOe) field [10].…”

“…So far, we have demonstrated a much larger ∆T c0 in comparison with TM SSVs together with an infinite MR. We now discuss the origins of these remarkable features. First we focus on ∆T c0 ; theoretical predictions [3,4] for TM SSVs ∆T c0 in the dirty limit can be two orders of magnitude higher than the corresponding experimental results [10,19]. To compare our results with theory, we used the Usadel equation to model our results in the dirty limit because the mean free paths of both epitaxial Nb and Ho (l Nb , l Ho ) were smaller than their respective coherence lengths (ξ Nb , ξ Ho ) [23].…”

Influence of the FFLO-like state on the upper critical field of a superconductor/ferromagnet bilayer: Angular and temperature dependence

“…for F/S/F and S/F/F structures), the superconducting transition temperature depends on the relative orientation of their magnetizations 26,27 . Such systems represent superconducting spin valves, which can be switched between two states with different transition temperatures by magnetic fields, as demonstrated experimentally for the F/S/F [28][29][30] and S/F/F [31][32][33] case. For non-collinear orientations of the magnetizations, an unconventional odd-in-frequency triplet s-wave pairing 23 is predicted, reducing the superconducting transition temperature 34 .…”