Long range proximity effects in planar structures involving the half-metal ferromagnet La 0.7 Sr 0.3 MnO 3   and   Pt interlayers

Over the past decade, there has been steady research on superconducting junctions with a ferromagnet as the weak link and where triplet correlations can transport supercurrents over a substantial distances. Of particular interest are half-metallic ferromagnets, in which only one spin band is present, so that, presumably, the induced supercurrent is fully spin polarized. We have earlier reported on a study of triplet transport in planar La₀. ₇Sr₀. ₃MnO₃ (LSMO) nanostrip Josephson junctions with NbTi superconducting contacts, where we found high values for the supercurrents, and large junction lengths (up to 1. 3 m). Here we extend that work by studying the dependence of the critical current I₂ on the length of the nanostrip between the contacts and the width of the strip. All junctions show strong supercurrents, but we do not observe simple systematics. Apparently, the fabrication process does not allow sufficient control over some of its parameters. To gain more insight in the mechanism for triplet generation at the LSMO/NbTi interface, we also studied the effect of Pt as an interlayer between the LSMO and the NbTi. For this, we etched a NbTi/Pt electrode structure on a full film of LSMO. The results are highly promising, showing sharp superconducting transitions and zero-resistance states being reached at an electrode distance of 2 m, with indications that larger distances should be feasible.