Anisotropy of the critical current density in epitaxialYBa2Cu3<

Abstract

The critical current density j c (B,T,0) of epitaxial, c-axis-oriented Yba2Cu30 x films was measured between 4.2 and 77 K in magnetic fields up to 8 T as a function of the field direction 0. Strongly enhanced critical currents are observed when the flux lines are aligned along the CuO planes, but there is also a maximum in j c when the magnetic field is adjusted parallel to the c axis. We relate these effects to an intrinsic pinning between CuO layers, an anisotropy of the shear modulus C66, and pinning effects of twin boundaries or stacking faults perpendicular to the film plane, respectively. PACS numbers: 74.60.Jg, 74.60.Ge, 74.75.+t Ceramic superconductors are well known to show a strong anisotropy in resistivity, critical current, and upper critical field B C 2. x A single-crystalline material is required to study the anisotropic behavior of the superconducting properties in detail. In this work the critical current density j c in epitaxial, c-axis-oriented films is investigated as a function of the magnetic field direction up to 8 T for various temperatures.The samples were prepared by laser deposition in an in situ process using a Siemens XP 2020 excimer laser (XeCl, 308 nm). 2 Epitaxial growth and c-axis orientation were achieved by heating the <100> SrTiC>3 substrates to about 800 °C and applying a 0.4-mbar oxygen atmosphere during the deposition. The 200-to 250-nmthick films were patterned to 10-/xm-wide and 180-jumlong strip lines using photoresist and wet-etching techniques. 3 The strip lines were randomly oriented with respect to the a-and &-axis directions in the YBa2Cu30 x films. Silver was evaporated as a contact material after sputtering the film surface for 40 sec with Ar ions. The contacts had to withstand currents of more than 1 A passing the strip line at 4.2 K and corresponding to y c 's up to 5x 10 7 A/cm 2 . j c , always measured perpendicular e^ A axis of rotation -CuO -layer -* flux line (b) Lorentz force _FL c-axis (a) flux t -CuO -layer Lorentz "* force _FL (c) twins, stacking faults FIG. 1. (a) Directions of current, magnetic field, and film normal and definition of the tilt angle 0. (b) Direction of the Lorentz force in the B-Lc case, (c) Direction of the Lorentz force in the Bile case.to the magnetic field direction for all angles 0, was determined by the four-probe technique with a voltage criterion of 0.5 ^V. The films were oriented with respect to the magnetic field direction from 0° to 180° as shown in Fig. 1(a). The current was reversed to simulate the range from 180° to 360°. The T c Gtf-0) of the film whose j c values are presented in this work was 89.1 K, the resistivity was 76 n O. cm at 100 K and 242 JJ, n cm at 300 K. Fig. 2. At T < 60 K a maximum of the critical current density is obtained when the magnetic field is aligned along the film plane. However, at 77 K and B < 2 T we observe higher j c values when B is perpendicular and parallel to the film plane. There is a crossover of the j c (B) curves perpendicular and parallel to the film plane. j c (B\\c) drops to zero b...

High Current-Carrying Capability inc-Axis-Oriented SuperconductingMgB2Thin Films

“…Based on the temperature dependence of J c measured at 0.5 T, the extrapolated value of J c at 5 K was estimated to be ∼40 MA/cm 2 . This value is comparable to that of YBa 2 Cu 3 O 7 thin film [21], and even exceeds the values for other HTS, such as Hgand Bi-based superconductors [22,23]. The high J c of ∼ 0.1 MA/cm 2 at 37 K under a self field suggests that MgB 2 thin films have very high potential for low-cost applications in electronic devices operating at high temperature, such as microwave devices and portable SQUIDs sensors, by using miniature refrigerators.…”

Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2epitaxial film with a high critical current density over 1 MA/cmSato1, Katase2, Kang3 et al. 2013Phys. Rev. B17170View full textAdd to dashboardCite

“…In MgB 2 and YBCO films without artificial pinning centers, it is estimated that their dominant intrinsic pinning centers are planar defects (i.e., grain boundaries and twin boundaries) due to the scaling behaviors of their normalized pinning force and transmission electron microscopy image. [42][43][44][45] On the other hand, the scaling behaviors of normalized pinning force and magnetic Bitter decoration indicate that BaFe 2 As 2 :Co has intrinsic pinning centers [11,46] and extrinsic c-axis pinning centers, which are also observed in Fig. 1 clearly, exist in BaFe 2 As 2 :Co epitaxial film.…”

Commensurate vortex lattices and oscillation effects in superconducting Mo/Si and W/Si multilayers

“…Such a movement is strongly hindered and occurs by the finite steps at rather high currents [6]. The important role of the intrinsic pinning, determining the orientational dependence of the critical current I c , was confirmed experimentally [36][37][38]. Intrinsic pinning also gives rise to such phenomenon as a lock-in transition [25].…”