Domain wall based spin-triplet Josephson junction and SQUID

Spin-singlet Cooper pairs convert to spin-triplet Cooper pairs on passing through a magnetic non-collinear structure at superconductor(S)/ferromagnet(F) interface [1]. In this context, the generation of triplet supercurrents through intrinsic ferromagnetic domain walls, which are naturally occurring non-collinear magnetic structure, was proposed theoretically in the last decade [2]. However, an experimental demonstration has been lacking in the literature, particularly due to the difficulty in accessing a single domain wall which is typically buried between two domains in a ferromagnetic material. In this report, by pinning a magnetic domain wall at the barrier of a nanoscale S/F/S planar junction, we have been able to demonstrate the predicted long-range triplet supercurrent due to a domain wall. The spin-triplet current was measured over a ferromagnetic barrier width exceeding 70 nm. Using the same concept of domain wall pinning at the Josephson junction barrier, we have also demonstrated a planar Nb/Ni/Nb triplet SQUID device.
[1]. J. Linder and J. W. A. Robinson, Nat. Phys. 11, 307 (2015).
[2]. F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 4096 (2001).