Superconducting Order Parameter Nucleation and Critical Currents in the Presence of Weak Stray Fields in Superconductor/Insulator/Ferromagnet Hybrids

The stray fields produced by ferromagnetic layers in Superconductor/Insulator/Ferromagnet (S/I/F) heterostructures may strongly influence their superconducting properties. Suitable magnetic configurations can be exploited to manipulate the main parameters of the hybrids. Here, the nucleation of the superconducting phase in an external magnetic field that periodically oscillates along the film width is studied on the base of the numerical solution of the linearized system of Usadel equations. In addition, the effect of the magnetic configuration of the F-layer on the temperature dependence of the critical current density, Jc(T), is investigated in the framework of the Ginzburg–Landau phenomenological theory on the base of the oscillating model of a stray field. By following this approach, the Jc(T) dependence of a Nb/SiO2/PdNi trilayer is reproduced for different magnetic configurations of the PdNi layer.

Controlling the proximity effect in a Co/Nb multilayer: the properties of electronic transport

We present both theoretical and experimental investigations of the proximity effect in a stack-like superconductor/ferromagnetic (S/F) superlattice, where ferromagnetic layers with different thicknesses and coercive fields are made of Co. Calculations based on the Usadel equations allow us to find the conditions at which switching from the parallel to the antiparallel alignment of the neighboring F-layers leads to a significant change of the superconducting order parameter in superconductive thin films. We experimentally study the transport properties of a lithographically patterned Nb/Co multilayer. We observe that the resistive transition of the multilayer structure has multiple steps, which we attribute to the transition of individual superconductive layers with the critical temperature, T c, depending on the local magnetization orientation of the neighboring F-layers. We argue that such superlattices can be used as tunable kinetic inductors designed for artificial neural networks representing the information in a “current domain”.

Controlling the proximity in a Co/Nb multilayer: the properties of electronic transport

We present both a theoretical and experimental investigation of the proximity effect in a stack-like superconductor/ferromagnet (S/F) superlattice, where ferromagnetic layers with different thicknesses and coercive fields are made of Co. Calculations based on Usadel equations allow us to find conditions at which switching from the parallel to the antiparallel alignment of neighboring F-layers leads to a significant change of the superconducting order parameter in thin s-films. Experimentally we study the transport properties of a lithographically patterned Nb/Co multilayer. We observe that the resistive transition of the multilayer contains multiple steps, which we attribute to the transition of individual s-layers with T c’s depending on the local magnetization orientation of neighbor F-layers. We argue that such superlattices can be used as tunable kinetic inductors, designed for artificial neural networks with a representation of information in the current domain.

Periodic Co/Nb pseudo spin valve for cryogenic memory

We present a study of magnetic structures with controllable effective exchange energy for Josephson switches and memory applications. As a basis for a weak link we propose to use a periodic structure composed of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on the Usadel equations show that switching from parallel (P) to antiparallel (AP) alignment of neighboring F layers can lead to a significant enhancement of the critical current through the junction. To control the magnetic alignment we propose to use a periodic system whose unit cell is a pseudo spin valve of structure F1/s/F2/s where F1 and F2 are two magnetic layers having different coercive fields. In order to check the feasibility of controllable switching between AP and P states through the whole periodic structure, we prepared a superlattice [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)]6 between two superconducting layers of Nb(25 nm). Neutron scattering and magnetometry data showed that parallel and antiparallel alignment can be controlled with a magnetic field of only several tens of Oersted.

Эффект близости в сверхпроводящем триплетном спиновом клапане S1/F1/S2/F2

Using the matrix method for solving linearized Usadel equations in the multimode approximation, the critical temperatures of the multilayer structures of the Superconductor / Ferromagnet / Ferromagnet (S/F/F) type has been obtained. The influence of an additional superconductor layer on the effects of the three-layer spin valve has been considered. In comparison with the additional normal layer in an S/F/N/F structure, the possibility of increasing the efficiency of the spin valve modes in a structure with an additional superconducting layer S instead of N has been discussed. The support by RSF (grant No. 18-12-00459) is gratefully acknowledged.