SIGN REVERSAL OF THE FLUX-FLOW HALL-EFFECT IN SPUTTERED A-AXIS-ORIENTED AND C-AXIS-ORIENTED FILMS OF 1/2/3-SUPERCONDUCTING CUPRATES

Films of RBa(2)CU(3)O(7) (R=Y, Ho, and Eu) have been obtained with c-axis orientation perpendicular to the film plane, by two dc sputtering methods, on different kinds of substrates. Also, pure a-axis-oriented films of EuBa2Cu3O7 have been grown by dc magnetron sputtering. The films have been characterized by x-ray diffraction, resistivity, and critical current. The Hall effect has been measured in the normal and in the mixed state using a magnetic field up to 9 T. The films show a strong anisotropy in the normal state, with n-type and p-type behaviors in a-axis and c-axis films, respectively. All the films show sign reversal of the Hall resistivity in the mixed state. The maximum positive value (a-axis films) and the minimum negative value (c-axis films) of the Hall-effect resistivity are sample dependent. The analysis of this result shows that the enhancement of the effect occurs when the samples are in the transition region between the dirty and clean regimes. Films with very different values of the mean free path l and coherence length xi(0) show a vanishing small effect in comparison with films that present l similar or equal to xi(0).