Fabrication of planar halfmetallic ferromagnetic Josephson junctions with long range coupling

Abstract

Superconducting junctions with a ferromagnet as the weak link, where triplet correlations can transport supercurrents over a substantial distance, have been of long-standing interest. In this work, we study the triplet transport in planar La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) nanowire Josephson junctions with NbTi superconducting contacts. By meticulous ion etching with an artificial Pt hard mask, the NbTi/LSMO bilayer is structured to form an LSMO bridge without damaging its top layer. We observe superconducting (critical) currents of the order of 10$^{9}$ A/m$^2$ in a junction with a length of 1.3 $\mu$m, and distinguishing superconducting quantum interference (SQI) patterns when sweeping a magnetic field perpendicular ($B_\perp$) to the plane of the wire or parallel ($B_\parallel$) to the plane and along the wire. The observed Gaussian-shaped SQI pattern is attributed to the diffusive transport of triplet pairs in the LSMO. Our work demonstrates that combinations of oxide magnets with conventional ($s$-wave) alloy superconductors can be a promising new route to realizing superconducting spintronics.