NOVEL PROXIMITY EFFECT BETWEEN HIGH-TC SUPERCONDUCTOR AND MAGNETIC MANGANESE OXIDE

A novel proximity effect between high-T(c) superconductor and magnetic manganese oxide has been found. Supercurrents were observed through La0.7 Ca0.3 MnOz (LCMO) magnetic barrier as thick as 500 nm in YBCO/LCMO/YBCO trilayered junctions. We confirmed this proximity effect in coplanar-type junctions with spacing of 200 nm, and presented a possibility that this phenomenon occurs between NbN and LCMO. Furthermore we investigated current-voltage (I-V) characteristics and magnetic properties for Y1Ba2Cu3Oy/La1-xSrxMnOz(200nm)/Y1Ba2Cu3Oy (YBCO/LSMO/YBCO) junctions. I-V characteristics changed systematically with varying the magnetism of the barrier. When x value was 0.2, supercurrents passed through the barrier, and it was found that ferromagnetism (Ms = 135 emu/cc) and supercurrents coexist in this proximity state. Magnetism of the LSMO is understood as a complicated and fluctuated state of ferromagnetic coupling in a-b plane and antiferromagnetic coupling along c-axis. Considering supercurrents passed through the La1-xSrx(Mn3+1-xMn4+x)Oz along c-axis, our results suggest a novel proximity effect mechanism, that is antiferromagnetic spin fluctuation and charge fluctuation can transport Cooper-pairs over a long range.