Superconducting mesa-structures with a spin filtering manganite interlayer

Abstract

We report on current transport and magnetism in hybrid superconducting mesa-structures prepared from epitaxial superconductor YBa2Cu3O7-δ and manganite LaMnO3 thin films. Superconducting Au-Nb bilayer was the top electrode. Measurements of magnetic resonance in heterostructure with the only Au top electrode (without Nb) showed ferromagnetic state close to Curie temperature of LaMnO3, 150 K. A spin filtering was revealed by measurements of tunneling magneto-resistance. Mesa-structures had no superconducting current even at reduced temperature T=300 mK and the smallest manganite interlayer thickness, dM=5.6 nm. Varying the external magnetic field |H|<10 Oe and dc bias current |I|<0.5 mA the microwave generation with power P <1 pW with a line-width of order 50 MHz was observed in GHz frequency band. The frequency of generation could be tuned by the biasing current with a rate 1013 Hz/A. The impact of spin polarized current on microwave generation is discussed taking into account the asymmetry of oscillation amplitudes over the applied magnetic field.