Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2 epitaxial film with a high critical current density over 1 MA/cm2

Abstract: The mixed-state Hall effect was examined in a Ba(Fe1-xCox)2As2 epitaxial film with a high critical current density. The transverse resistivity {\rho}xy and the longitudinal resistivity {\rho}xx follow power law scaling {\rho}xy = A{\rho}xx{\beta}. In the temperature-sweep with a fixed field (T sweep), all of the {\beta} values are independent of magnetic field up to 9 T, and are lower than 2.0 (around 1.8). In contrast, the {\beta} values in the magnetic-field sweep with a fixed temperature (H sweep) change from 1.8 to 2.0 as the temperature increases from 13 to 16 K even in the T/H region that overlaps with the T sweep measurements. These results indicate that the vortices introduced at low temperatures are trapped by strong pinning centers, but a portion of the vortices introduced at high temperatures are not strongly trapped by the pinning centers. The sign of {\rho}xy is negative, and a sign reversal is not detected. These distinct scaling behaviors, which sharply contrast cuprates and MgB2, are explained by high-density c-axis pinning centers in the Ba(Fe1-xCox)2As2 epitaxial film and are consistent with a wider vortex liquid phase.