Spin-polarized quasiparticles injection in La0.7Sr0.3MnO3/SrTiO3/Nb heterostructure devices -: art. no. 122505

We report the effect of spin-polarized quasiparticle injection from a ferromagnetic manganite into a conventional Nb superconductor in a La0.7Sr0.3MnO3/SrTiO3/Nb heterostructure. A 8-terminal stacked trilayer geometry was used, where the injected current I-inj enters a superconducting microbridge and leaves it symmetrically by tunneling through a SrTiO3 barrier. A high dynamic gain G=-dI(c)/dI(inj) was observed from 1.7 up to 8.5 K, where I-c is the microbridge critical current. For a dc injection current, G was measured to be 290 at 1.7 K. A SrTiO3 barrier of thickness in the range 3.5-8.5 nm was found to provide a suitable spin injection length of the order of the bridge length and a low Joule heating level. In this confined stacked device geometry it was found that Joule dissipation in the manganite and barrier does not contribute significantly to the suppression of I-c, in contrast with previous studies. (C) 2005 American Institute of Physics.