Multiterminal Superconducting-Ferromagnetic Device with Magnetically Tunable Supercurrent for Memory Application

We report on the fabrication and testing at 4.2 K of four-terminal SF₁IF₂S₁IS₂ devices, where S denotes a superconductor (Nb), F_1,2 denotes ferromagnetic material (permalloy (Py) and Ni, respectively), and I denotes an insulator (AlO_x). The F_{1 IF}2 structure plays a role of a pseudospin 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. The two different magnetization orientations in the F₁ and F₂ layers can be sensed by an adjacent S_{1 IS}2 junction, resulting in the two distinct Josephson critical current values. Such controlled manipulation of the Josephson critical current offers a 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 the single flux quantum circuit elements. We present a theoretical model that adequately describes the experimental results.