Superconducting devices with ferromagnetic insulating GdN

Abstract

A thin Superconductor (S) proximity coupled to a Ferromagnetic Metal (FM) is an experimentally well studied system showcasing intriguing phenomena such as an oscillatory T_c with FM thickness, zero to pi transitions in S/FM/S Josephson Junctions (JJs), and the possibility of generation of spin polarized Cooper pairs using conventional s-wave superconductors [1,2]. However, the proximity coupling of a Ferromagnetic Insulator 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 a thin S layer, which is distinctly different from that of the stray field emanating out of the FI layer [3]. Most studies of FI/S systems have thus far been performed with various Europium chalcogenides. In this talk, I will discuss few superconducting devices using ferromagnetic insulator – GdN, which has been developed at the Quantum Materials and Devices Laboratory at IIT Bombay. The first is an FI/S bilayer, which is demonstrated as a system that allow application and tuning of local magnetic fields [4]. The second device is a large mesa type S/FI/S JJ; where a combination of barrier magnetization and magnetization due to junction self-current, leads to a zero magnetic field non-reciprocal Josephson effect (Josephson Diode). A non-volatile Josephson memory with reasonably high characteristic voltage is also demonstrable in such large magnetic JJs with GdN tunnel barrier.