FLUCTUATION MAGNETOCONDUCTIVITY IN FE DOPED YBA2CU3O7-DELTA SIGN CHANGE FOR B AND I PARALLEL TO THE PLANES

The magnetoconductivity in Fe doped YBa2Cu3O7-delta single crystals ha s been measured in the temperature region above T-c where superconduct ing fluctuations are known to be important. For small Fe concentration s and B parallel to c we obtain excellent agreement with accepted fluc tuation theories. However, at higher Fe concentrations this descriptio n seems to break down. For B perpendicular to c we observe an anomalou s dependence on the relative orientation of current and field, both ap plied along the ab-planes. For B parallel to I the magnetoconductivity is negative, as expected. For B perpendicular to I we observe a cross -over to a positive magnetoconductivity above about T-c + 10 K.