Spin-polarized injection into YBaCu3O7 grain boundary junctions

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YBa 2 Cu 3 O 7 / SrTiO 3 / La 0.67 Ca 0.33 MnO 3 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 LT 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 I0 and area density 108 A m−2, have been injected into the GBJ region by using an offset current method. The I0(B) characteristics of the GBJ under injection suggest that the suppression of I0 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.