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.

Abnormal behaviour of the resistive transition to the normal state in superconducting Nb-Ti tapes just below Hc2

The results of studying the resistive properties of Nb-Ti tapes in high magnetic fields close to the upper critical field (Hc2) are reported. The voltage-current curves (VCCs) and resistance-current cures (RCCs) show an “abnormal” hysteresis which is opposite in sign to a common thermal one caused by self-heating. Several features were noted: the existence of threshold current below which VCCs are reversible and the presence of excessive voltage noise in the hysteresis region. Earlier the similar behaviour was observed in granular superconductors. The nature of the “granular” properties of Nb-Ti tapes in high magnetic field and the relation with other observed effects, such as the irreversibility field and the apparent anisotropy of the upper critical field are discussed.