Fig. 1

Four-probe non-local configurations for resistance measurements of a non-magnetic/ferromagnetic/non-magnetic (NFN) sandwich, when the СPP charge flow is driven from source I_S to drain I_D and the voltage drop is measured between two other nodes bounding the related conditional resistor(s). (a) Conventional four-resistor model^24,25,26 with the crossed configuration of current and voltage contacts. (b) Circuit diagram with six conditional resistors for R_{AB, CD} measurements. (c) Schematics of the through-N/F/N sample four-terminal configuration with contacts B and D made of Pt, two NbN superconducting films with contacts A and C, and the ferromagnetic interlayer F in grey, blue, and yellow, respectively. The currents I_XY mean the net currents flowing from contact X to contact Y (X, Y = A, B, C, D and X ≠ Y), the arrows correspond to the expected directions of the charge flow and, accordingly, to positive current values. If, due to the charge transport redistribution, the current between the two nodes, by which the voltage drop is determined, changes its direction (and consequently the voltage drop changes its sign), the four-probe resistance calculated using Eq. (1) will be negative.