Experimental study of the feasibility of a spin valve based on superconductor/ferromagnet proximity effect
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Experimental Study of the Feasibility of a Spin Valve Based on Superconductor/Ferromagnet Proximity Effect I. A. Garifullina, N. N. Garif’yanova, R. I. Salikhova, K. Westerholtb, D. Sprungmannb, H. Zabelb, R. Brucasc, and B. Hjörvarssonc a
b
Zavoisky Physical-Technical Institute, Kazan, 420029 Russia Institute for Experimental Physics/Condensed Matter Physics, Ruhr-Universität Bochum, D-44780 Bochum, Germany c Department of Physics, Uppsala University, Box 530, SE-751 21 Uppsala, Sweden e-mail: [email protected]
Abstract—The feasibility of a superconducting spin valve based on superconductor/ferromagnet proximity effect is discussed. Experimental results obtained by the authors to date in studies of this problem are presented. PACS numbers: 74.45.+c, 74.78.Fk, 74.62.-c DOI: 10.1134/S1063776107070503
1. INTRODUCTION The interaction between superconductivity and ferromagnetism in layered thin-film superconductor/ferromagnet (S/F) heterostructures (S/F proximity effect) has been the subject of extensive studies over the past decade. To date, many characteristics of the S/F proximity effect are well understood (e.g., see reviews in [1–6]), and currently growing interest in this effect is motivated by its potential applicability in spintronics [7–12]. In multilayer thin-film systems, the superconducting transition temperature Tc can be controlled by relative orientation of F-layer magnetizations. Originally, a superconducting spin-valve design based on the S/F proximity effect was proposed by Sangjun Oh with coauthors in [7]. It was the S/F1/N/F2 system shown in Fig. 1a, where the F1 and F2 layer magnetizations are decoupled by a nonmagnetic metal (N) layer sufficiently thin to transmit the Cooper pair wavefunction from the S layer into the F2 layer. In the F1/S/F2 spin valve design theoretically proposed by Tagirov in [8] (see Fig. 1b), the S layer is adjoined by F layers on both sides. Calculations show that Tc is lower for both structures with parallel orientation of the F-layer magnetizations as compared to their antiparallel orientation. Generally, the relative orientation of the ferromagnetic magnetizations can be varied by using an antiferromagnetic film deposited on the F2 layer (see Fig. 1), which fixes the F2-layer magnetization via anisotropy fields. This scheme makes it possible to rotate the F1-layer magnetization by applying a relatively weak external magnetic field. Two recent reports of Tagirov’s superconducting spin-valve design implemented in CuNi/Nb/CuNi trilayers can be found in [9, 10], and an observation of the effect in a Ni/Nb/Ni system was
reported in [12]. The difference in Tc between parallel and antiparallel magnetizations of CuNi ferromagnetic layers, [∆Tc], was found to be approximately 6 mK. For the Ni/Nb/Ni system, it amounted to 41 mK. One prerequisite for observing a significant superconducting spin valve effect is reentrant superconductivity [8]. We discovered this phenomenon in Fe/V/Fe trilayers [13]: as the Fe layer thickness dFe was increased, superconductivity va
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