Enhancement of low field magnetoresistance in YBa/sub 2/Cu/sub 3/O/sub 7//Nd/sub 0.7/Sr/sub 0.3/MnO/sub 3/ heterostructures

In order to obtain an enhancement of low field magnetoresistance (MR) in Nd/sub 0.7/Sr/sub 0.3/MnO/sub 3/ (NSMO) films, two kinds of superconducting flux focusing devices made of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) have been fabricated. In the superconducting state, YBCO expels magnetic flux from its interior and focuses the magnetic flux on a bridge of NSMO film. Using such a magnetic "lens", at temperatures below 77 K, /spl sim/900% enhancement in MR was observed. This corresponds to more than 15% change in the MR of NSMO in the presence of a couple of hundred Gauss. In order to successfully integrate high-T/sub c/ superconductivity with the magnetoresistive effect, bilayers of YBCO/NSMO were in situ deposited on (100) LaAlO/sub 3/ substrates by pulsed laser deposition so that the peak resistance temperature (T/sub p/) of NSMO was below the superconducting transition temperature (T/sub c/) of YBCO. X-ray diffraction and Rutherford Backscattering Spectroscopy (RBS) measurements provide evidence of epitaxial growth of YBCO/NSMO heterostructures.