Remotely induced magnetism in a normal metal using a superconducting spin-valve

Superconducting spintronics has emerged in the last decade as a promising new field that seeks to open a new dimension for nanoelectronics by utilizing the internal spin structure of the superconducting Cooper pair as a new degree of freedom. Conventional Cooper pairs are in a spin singlet state, with oppositely aligned spins. The basic building blocks of superconducting spintronics, however, are spin-triplet Cooper pairs with equally aligned spins. Such states are promoted by proximity of a conventional superconductor to a ferromagnetic material with inhomogeneous macroscopic magnetization. A multitude of proof-of-principle type experiments were successfully performed. Currently, the discipline finds itself at the crossroads for developing first-generation devices. One still unresolved issue concerns experimental verification of a theoretically predicted inverse magnetization induced inside a conventional superconductor contacted by a ferromagnet. In search for this phenomenon, using low-energy muon spin rotation experiments, we found an entirely unexpected novel effect: the creation of a magnetization at a remote non-magnetic interface between a metal (gold) and a superconductor (niobium), separated from a ferromagnetic double layer by a distance >50 nm. This remote magnetization depends on the mutual orientation of the magnetizations in the ferromagnetic double layer: it takes its maximum at perpendicular alignment, while it disappears when switching our device into a homogeneous magnetic state. Surprisingly, we observe no magnetization in the superconductor itself. In all respects, the entire structure thus shows unusual non-local spin-valve behaviour, acting over a distance. The effect disappears when the superconductor switches to the normal state. This provides the intriguing possibility to detect remotely the magnetic state of a device via a dissipationless superconducting conduit. It may act as a basic building block for a new generation of quantum interference devices based on the spin of a Cooper pair.