Superconducting Spin-Valve Effect in Structures with a Ferromagnetic Heusler Alloy Layer
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Superconducting Spin-Valve Effect in Structures with a Ferromagnetic Heusler Alloy Layer A. A. Kamasheva,b,*, N. N. Garif’yanova, A. A. Validova, Ya. V. Fominovc, and I. A. Garifullina a Zavoisky
Kazan Physical–Technical Institute, Federal Research Center “Kazan Scientific Center,” Russian Academy of Sciences, Kazan, 420029 Russia b Kazan Federal University, Kazan, 420008 Russia c Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia *e-mail: [email protected] Received February 18, 2020; revised February 18, 2020; accepted February 18, 2020
Abstract—We present comparative analysis of superconducting properties of two types of spin valves containing Heusler alloy Co2Cr1 – xFexAly as one of ferromagnetic layers (F1 or F2) in the F1/F2/S structures. We have used the Heusler alloy layer (i) as a weak ferromagnet in the case of the F2 layer and (ii) as a half-metal in the case of F1 layer. In the former case, large classical effect ΔTc of the superconducting spin valve is obtained; this is facilitated by a substantial triplet contribution ΔTctrip to the superconducting spin valve effect. In the latter case, giant value of ΔTctrip reaching 0.5 K is observed. DOI: 10.1134/S1063776120060126
1. INTRODUCTION Investigations of the interrelation between two antagonistic phenomena (superconductivity and ferromagnetism) have been performed from the middle of 1960s. The antagonism of these phenomena is related to the fact that ferromagnetism presumes parallel (P) spin orientation, while superconductivity presumes antiparallel (AP) orientation because the spins of electrons constituting a Cooper pair have opposite directions. Due to considerable advances in preparing high-quality thin layered metal films (multilayers) in recent years, the direction of research works has been shifted towards artificially obtained multilayer heterostructures (see, for example, reviews [1–3]). The interest in structures consisting of ferromagnetic and superconducting layers is due to the fact that superconductivity (S) and ferromagnetism (F) in them are spatially separated. The phenomena observed in such structural materials are known as superconductor/ferromagnet (S/F) proximity effect. In the last two decades, huge theoretical and experimental interest in the development of logical elements for superconductor spintronics (see, for example, [4, 5]) was demonstrated. According to these publications, the most promising devices for application in quantum logic elements are heterostructures based on the S/F proximity effect [6]. The quantum qubit element [7, 8] is based on the so-called Josephson π junction [9, 10], which can be obtained in a thin-film
S/F/S heterostructure. In this respect, the S/F interface has become of fundamental importance [11]. In particular, in 1997, a group headed by Prof. Beasley from the Stanford University [12] proposed a theoretical model of a superconducting spin valve (SSV) based on the fact that the degree of
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