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 SF
₁
IF
₂
S
₁
IS
₂
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 F
₁
and F
₂
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.