Superconducting-ferromagnetic injection-controlled switching device

We report the fabrication and characterization at 4.2 K of superconducting-ferromagnetic (SIFS) switching devices that are configured in an injection-controlled weak link geometry (ICWL). Here, S, I, and F denote a superconductor (Nb), an insulator (Al/AlO_x), and a ferromagnetic material [Ni or Ni₈₀Fe₂₀ (Py)], respectively. An ICWL device can be designed to have a broad range of output resistances. Therefore, such devices can serve as line drivers and cell selectors in cryogenic memories involving currently developed magnetic memory elements. These devices can have a critical current gain well above 10. We have found that performance of our ICWL devices can be explained by the 'simple heating' model, which corresponds to the result obtained for SIN devices with similar configurations studied earlier by others [K. Takeuchi and Y. Okabe, 'Gap measurement in Nb/NbOx/Al injection controlled planar three terminal devices,' IEEE Trans. Magn., vol. 25, pp. 1282-1285, Mar. 1989]. However, an advantage of the SIFS devices over SIN devices is that the F layer can be made very thin with a negligible resistance as compared with the tunnel barrier resistance.