Increasing the performance of a superconducting spin valve using a Heusler alloy

We have studied superconducting properties of spin-valve thin-layer heterostructures CoOx/F1/Cu/F2/Cu/Pb in which the ferromagnetic F1 layer was made of Permalloy while for the F2 layer we have taken a specially prepared film of the Heusler alloy Co2Cr1-xFexAl with a small degree of spin polarization of the conduction band. The heterostructures demonstrate a significant superconducting spin-valve effect, i.e., a complete switching on and offof the superconducting current flowing through the system by manipulating the mutual orientations of the magnetization of the F1 and F2 layers. The magnitude of the effect is doubled in comparison with the previously studied analogous multilayers with the F2 layer made of the strong ferromagnet Fe. Theoretical analysis shows that a drastic enhancement of the switching effect is due to a smaller exchange field in the heterostructure coming from the Heusler film as compared to Fe. This enables to approach an almost ideal theoretical magnitude of the switching in the Heusler-based multilayer with a F2 layer thickness of ca. 1 nm. © 2018 Kamashev et al

Layered ferromagnet-superconductor structures: the π\pi state and proximity effects

We investigate clean mutilayered structures of the SFS and SFSFS type, (where the S layer is intrinsically superconducting and the F layer is ferromagnetic) through numerical solution of the self-consistent Bogoliubov-de Gennes equations for these systems. We obtain results for the pair amplitude, the local density of states, and the local magnetic moment. We find that as a function of the thickness $d_F$ of the magnetic layers separating adjacent superconductors, the ground state energy varies periodically between two stable states. The first state is an ordinary "0-state", in which the order parameter has a phase difference of zero between consecutive S layers, and the second is a "$\pi$-state", where the sign alternates, corresponding to a phase difference of $\pi$ between adjacent S layers. This behavior can be understood from simple arguments. The density of states and the local magnetic moment reflect also this periodicity.Comment: 12 pages, 10 Figure

Nickel on Lead, Magnetically Dead or Alive?

Two atomic layers of Ni condensed onto Pb films behave, according to anomalous Hall effect measurements, as magnetic dead layers. However, the Ni lowers the superconducting T_{c} of the Pb film. This has lead to the conclusion that the Ni layers are still very weakly magnetic. In the present paper the electron dephasing due to the Ni has been measured by weak localization. The dephasing is smaller by a factor 100 than the pair-breaking. This proves that the T_{c}-reduction in the PbNi films is not due magnetic Ni moments

Proximity Effect in Heterostructures Based on a Superconductor/Half-Metal System

We have demonstrated that with increasing the exchange splitting of the conduction band of a ferromagnet and, respectively, of the degree of the spin polarization, the probability of transmission of the superconducting Cooper pairs through the S/F interface decreases. We have concluded that the spin imbalance plays a key role in the processes taking place at the interface between a superconductor and a ferromagnet with spin-polarized conduction electrons. We have studied the superconducting spin-valve effect in F1/F2/S heterostructures containing the Heusler alloy Co2Cr1 –xFexAly as one of two ferromagnetic (F1 or F2) layers. We have used the Heusler alloy layer in two roles: as a weak ferromagnet on the place of the F2 layer and as a half-metal on the place of the F1 layer. In the first case, we have obtained the full switching between the normal and superconducting states is realized with the dominant aid of the long-range triplet component of the superconducting pair condensate which occurs at the perpendicular mutual orientation of magnetizations. In the second case, we have observed separation between the superconducting transitions for perpendicular and parallel configurations of magnetizations reaching 0.5 K. We have also found good agreement between our experimental data and theoretical results

Superconducting Spin-Valve Effect in Structures with a Ferromagnetic Heusler Alloy Layer

© 2020, Pleiades Publishing, Inc. 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

Proximity effect in Fe/Pb/Fe trilayers

74.80.Dm Superconducting layer structures: superlattices, heterojunctions, and multilayers , - 74.50.+r Proximity effects, weak links, tunneling phenomena, and Josephson effects , - 74.62.-c Transition temperature variations,

FMR Studies of Exchange-Biased Heusler Alloy Thin Films

© 2020, Springer-Verlag GmbH Austria, part of Springer Nature. Ferromagnetic resonance (FMR) and SQUID-magnetization measurements were performed out to assess the potential of using the antiferromagnetic IrMn compound as an exchange-bias layer for the Heusler alloy layer Co 2Cr 1-xFe xAl y in the superconducting spin valve structure. It was observed that the exchange-bias field for the Heusler alloy film deposited directly on IrMn is close to zero. Introducing the Py (Ni 0.8Fe 0.2) interlayer between the IrMn and Heusler alloy layers improves the biasing property, but it is not enough for using it in the superconductivity spin valve. Furthermore, it was found that the magnitude of the exchange-bias field determined from the FMR data is several times smaller that obtained from the SQUID-magnetization measurements