Orientation Dependence of Critical Currents in a-Axis Oriented YBCO Thin Films

Thin films of YBCO with a high degree of alignment both normal to and within the basal plane have been prepared by an electron beam multilayer deposition technique. The a-axis oriented film consists of an array of orthogonal, interconnecting, rectangular crystal bars. The zero field critical current density for the a-axis oriented film measured with the magnetic field perpendicular to the plane of film is 6.7×10 6A/cm 2 at 4.4K and 1.2×105A/cm2 at 77K. In order to study the orientation dependence of the in-plane critical currents, the film was positioned so that the magnetic field was at angles of 0°, 30°, and 45° to the in-plane axes of the substrate. The critical current density J,(θ=0°) is 1.6 times larger than Jc(θ=45°) and Jc(θ=30°). These results imply that the degree of alignment of the crystal grains is crucial for achieving high quality thin films. The superconducting critical current density can be rather high, not only in the c-axis oriented films but also in the epitaxial a-axis oriented films, which have high degree of texture and excellent intergrain contact.