Superconducting devices with ferromagnetic insulators

A thin Superconductor (S) proximity coupled to a Ferromagnetic Metal (FM) is an experimentally and theoretically well studied system, which has demonstrated intriguing phenomena such as oscillatory Tc with ferromagnet thickness, zero to pi transitions in ferromagnetic weak link Josephson junctions and the possibility of generation of spin polarized Cooper pairs using conventional s-wave superconductors. However, despite some early studies from Meservey, Tedrow and Moodera in MIT – the proximity coupling of a Ferromagnetic Insulator (FI) to a superconductor, is relatively less explored. The primary feature of proximity coupling in FI/S systems is the appearance of an effective exchange field in the thin S layer, which is distinctly different from that of the stray field emanating out of the FI layer. In this talk I will discuss three different kind of superconducting devices using FIs which has been developed at the Quantum Materials and Devices Laboratory at IIT Bombay. The first is a FI/S bilayer, which we demonstrate as a system that allow application and tuning of local magnetic fields. The second is a FI/S/FI spin valve where several novel switching phenomena, and possible control of magnetism using superconductivity is found. Both these devices are in Current In-Plane (CIP) geometry, that harness the induced exchange fields for their functionality. In Current Perpendicular to Plane (CPP) geometry, using S/FI/S Josephson junctions – we demonstrate devices that exhibit non-reciprocal Josephson effect (Josephson Diode) and also non-volatile Josephson memory with reasonably high characteristic voltage.