Spin-polarized injection into YBa₂Cu₃O₇ grain boundary junctions

YBa2Cu3O7/SrTiO3/La0.67Ca0.33MnO3 trilayer thin films grown on bicrystal substrates were patterned into a structure that allows the injection of spin-polarized current into the region of a grain boundary junction (GBJ). The transfer length L-T was determined to ensure that injection was over the entire device width, in contrast to previously reported experiments. Currents up to some 100 times the junction critical current I-0 and area density 10(8) A m(-2), have been injected into the GBJ region by using an offset current method. The I-0(B) characteristics of the GBJ under injection suggest that the suppression of I-0 can be explained by a combination of heating and self-field effects, without any need to invoke the spin-polarized nature of the injected current. We find no evidence of direct injection into the junction. (C) 2003 American Institute of Physics.