Optimized sputtered YBa2Cu3O7 (YBCO) thin films on CeO2-buffered sapphire substrates are patterned into square lattices of submicrometer holes (antidots) with diameters of 250–450 nm and lattice parameters of d=500–1000 nm without deterioration of superconducting properties. In the mixed state, matching effects between the Abrikosov vortex lattice and the artificial antidot lattice are observed. These effects are in the form of peaks or cusps in the critical current density recorded as a function of magnetic induction at integers n and specific rationals k/l of the matching field Bm=(Φ0/d2). The experimental results are discussed in the context of existing theories. The existence of multiquanta vortices confined by the holes in YBCO films are considered.

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Large-area (001) oriented epitaxial CeO2 films with extremely high crystalline perfection characterized by x-ray diffraction rocking curves of the (002) CeO2 reflection with a full width at half maximum (FWHM) Δω⩽0.013° and thickness dependent oscillations in the Bragg-Brentano x-ray diffraction spectra were deposited via rf-magnetron sputtering on (11_02) sapphire. Pole figure measurements of the space symmetry confirmed that the examined sharp reflections belong to CeO2 and no other phases like CeAlO3 are present. The improvement of the crystalline quality was obtained by optimization of the high-pressure sputter deposition process and the use of large-area substrates. The [100] CeO2 axis was slightly tilted with respect to the [11_02] sapphire axis by 0.185°. Subsequently sputter-deposited high-Tc YBa2Cu3O7−x thin films revealed structural properties characterized by FWHM <0.06° of the (005) θ-2θ peaks and by FWHM of the (005) peaks rocking curves of Δω=0.3°.

This article will discuss improved electronically formed gradiometers based on high-temperature radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. For gradiometer balancing, a system of adjustable superconducting plates was developed. This technique was used to build first- and second-order, axial gradiometers with adjustable baselines, which operate at 77 K. Each magnetometer combines a washer rf-SQUID with bulk or a thin-film flux concentrator in flip chip geometry. In an unshielded environment, the magnetic field sensitivity in the white noise region is about 80 fT/√Hz for first-order and 150 fT/√Hz for second-order gradiometer. Common mode rejection could be balanced to better than 104 for uniform background fields and better than 200 for gradient fields.

Ab~truct-YBa~Cu~0~-, thin films were prepared on 2 inch in diameter (1102) sapphire substrates buffered with Ce02 layer of mixed (001)/(111) orientation. The thickness of the YBazCu307., films was typically -250 nm. The YBa2C~307-x thin films exhibited smooth surfaces (peak-to-valley roughness of less than 20 nm) free of cracks and outgrowths. The critical temperatures of these films were 87 -89 K, the critical current densities (2-3).106 Mcm2 at 77 K and zero magnetic field. The low field microwave surface resistance (Rs) of the YBa2C~307-n films was measured at 18.7 GHz. Values of -1.4 mR were obtained at 77 K and < 70 pR below 20 K. Such low Rs values are comparable to the lowest reported values for thicker YBa2Cu307., films grown epitaxially on structurally well-matched substrates, e.g. LaA103. The elevation of the microwave power produced a weak increase of R,. No drastic changes in Rs occur up to the maximum magnetic field of -35 Oe at 79 K and -63 Oe at 50 K. The properties of the YBa2Cu30,-x films do not degrade with time.