Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2epitaxial film with a high critical current density over 1 MA/cm

Abstract

The mixed-state Hall effect was examined in a Ba(Fe 1-x Co x ) 2 As 2 epitaxial film with a high critical current density. The transverse resistivity ρ xy and the longitudinal resistivity ρ xx follow power law scaling ρ xy = Aρ xx β . In the temperature-sweep with a fixed field (T sweep), all of the β values are independent of magnetic field up to 9 T, and are lower than 2.0 (around 1.8). In contrast, the β 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 ρ xy is negative, and a sign reversal is not detected. These distinct scaling behaviors, which sharply contrast cuprates and MgB 2 , are explained by high-density c-axis pinning centers in the Ba(Fe 1-x Co x ) 2 As 2 epitaxial film and are consistent with a wider vortex liquid phase. H. Sato et al. 3

Longitudinal and transverse Hall resistivities in NaFe1−xCoxAs single crystals withx= 0.022 and 0.0205: weak pinning and anomalous electrical transport properties

“…Apparently the disappearance of anomalous Hall effect observed in the weak-pinning NFCA is consistent with these arguments. It is noted that the Ba(Fe 1−x Co x ) 2 As 2 film with high-density pinning centers does not exhibit any sign reversal of Hall resistivity as recently reported by Sato et al [22]. Their observation is similar to that in an experiment of Budhani et al [23] where a diminishing sign anomaly of the mixed-state Hall resistivity in Tl 2 Ba 2 Ca 2 Cu 3 O 10 films with increasing columnar defects was reported.…”

High critical-current density with less anisotropy in BaFe2(As,P)2 epitaxial thin films: Effect of intentionally grown c-axis vortex-pinning centers

“…Therefore, by the vertical white arrows in Fig. 4, many vertical defects, which occur at a higher density compared with that found for BaFe 2 As 2 :Co films, [36] are observed in the STEM images. The number of defects did not significantly differ between the BaFe 2 As 2 :P films grown at 2.2 Å/s and 3.9 Å/s, but the shape and microstructure of the defects did differ.…”

Magnetic scattering and electron pair breaking by rare-earth-ion substitution in BaFe2As2epitaxial films

“…In the Ce-doping case (a), a resistivity drop without zero resistivity was observed for x film = 0.09, but the resistivity anomaly was still observed at T anom = 70 K. With a further increase in x film , the resistivity anomaly was not detected in the ρ-T curves, and T onset c for a superconductivity transition appears at x film 0.09. is the offset critical temperature determined by extrapolating a ρ − T curve to zero resistivity) of this film is 4.5 K, which is doubly larger than T c = 2.7 K of La-doped films [18] although the crystalline qualities are almost the same as seen in φ, ω and 2θ in figures 2(b) and (c), and the dopant distribution is homogeneous, which is confirmed by both EPMA (see supplementary figure S2(a), available from stacks.iop.org/NJP/15/073019/mmedia) and XRD (peak shift and broadening are not observed by Ce doping). Thus, the broad resistivity transition reflects a wide vortex liquid phase due to strong vortex pinning centers, similar to that of the Co-doped BaFe 2 As 2 epitaxial film [27,28]. The wide liquid phase is due to disorder in the films, which may also be the case in the Ce-doped films.…”