Automated manufacturing of segmented nanowires with thin ferromagnetic layers: a step towards miniature SFS Josephson junctions

Abstract

Superconducting electronics is a rapidly growing field in micro- and nanoelectronics. Various planar structures, such as Josephson junctions, exhibit intriguing phenomena with potential applications in spin-based and quantum devices. However, the integration density of these thin-film digital components is still lower than that of semiconductor elements. The nanometer-scale miniaturization of Josephson junctions can be achieved by using a new approach, such as nanowire-based geometry. This article reports an automated electrochemical method for producing segmented Au/Ni/Au nanowires with diameters less than 100 nm. The potentiostatic electrodeposition of metals from different baths using coulometric control leads to the formation of segments with narrow length distributions and well-defined boundaries. The ability to fabricate coarse-grained gold segments and single-crystal ferromagnetic nickel layers as thin as 7 nm has been demonstrated. For a nanowire-based Nb/Au/Ni/Au/Nb hybrid structure with planar Nb electrodes and a 7-nm-thick Ni segment, a critical current of 0.6 μA at 1.2 K has been detected. The low-temperature transport properties are described by an effective resistance model, in which the Ni ferromagnetic layer exhibits ballistic electron transport. The fabricated structures represent the first example of miniature SFS Josephson junctions based on individual segmented nanowires that demonstrate proximity-induced superconducting behavior. These findings pave the way for designing compact, F-containing digital devices for superconducting nanoelectronics and spintronics.