Memory Cell for High-Density Arrays Based on a Multiterminal Superconducting-Ferromagnetic Device

We report the fabrication and testing, at 4.2 K, of four-terminal SIS′F1IF2S devices, where S(S′) denotes a superconductor (Nb), F1,2 denotes a ferromagnetic material (Ni and permalloy (Py), respectively), and I denotes an insulator (AlOx). The F1IF2 junction plays the role of a pseudo-spin valve, in which the magnetization vector of the Py layer can be reversed either by an externally applied magnetic field, or, potentially, by the electric current properly supplied to the device. The total magnetic moment of the F1IF2 junction, determined by two different magnetization orientations in the F1 and F2 layers, can be sensed by an adjacent SIS′ junction, resulting in two distinct maximum Josephson critical current values. Such controlled manipulation of the Josephson critical current offers the possibility of building a cryogenic memory cell based on the four-terminal hybrid S/F device. One of the advantages of this memory device is its compatibility with single-flux quantum circuit elements.