Figure 1. Illustration of the transistor geometry and potential energy distribution.

(a) Ni₈₁Fe₁₉ permalloy disks (gray circles) of radius, R, and thickness, τ_m are designed with a small gap of distance, d. A gate electrode (gold wire) is overlaid with its left edge shifted from the opposing gap side by a distance, λ. A magnetized cell (black circle) of radius, a, is shown moving along the magnetic track. The external field direction, H_ext, is aligned along the track axis, depicted as the black arrow. The potential energy line cross-section simulated at a vertical height of z = a is shown in (b) from finite element (FEM) analysis (black line), and from analytical charge model (red line) based on Eqs. 1–2. A photograph of the chip and 3D printed container used to test the transistors are shown in (c). The overall instrument apparatus is shown in (d).