A method for the analysis of temperature and field dependent magnetization data near the Curie temperature T C is devised, which allows the reliable determination of critical
We report on the magnetic and superconducting properties of La 0.7 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7 ͑LCMO/ YBCO͒ superlattices. For a constant LCMO layer thickness of 6 unit cells ͑u.c.͒, resistance and susceptibility measurements show superconductivity for YBCO layer thickness in excess of 4 unit cells. The critical temperature increases with YBCO thickness, and a T c of 58 K is found for a YBCO thickness of 10 unit cells. Magnetization measurements show a ferromagnetic transition at 100 K in a (LCMO 6 u.c. /YBCO 5 u.c. ͒ 15 bilayer superlattice, and a depressed value of the saturation magnetization of 20 emu cm
Ϫ3. These results are discussed in terms of interface disorder ͑analyzed by x-ray diffraction and transmission electron microscopy͒ and of the possible interaction between magnetism and superconductivity.
La 0.67 Ca 0.33 MnO 3 - δ thin films were deposited using a high-pressure dc-sputtering process. Pure oxygen at a pressure of 3.8 mbar was used as sputtering gas. The films were grown on (001) LaAlO 3 and (001) SrTiO 3 substrates at heater temperature of 850° without any annealing treatment. The formation of highly a-axis-oriented films with sharp interface with substrate surface is demonstrated by X-ray diffraction, transmission electron microscope (TEM), and atomic force microscope (AFM) analysis. Electrical characterization revealed a metal–insulator transition at T MI = 276 K, and magnetic characterization showed good magnetic properties with a PM–FM transition at TC ≈ 262 K.
In this work we report the fabrication of superconductor loops, formed by an array of two Josephson junctions (JJ) in parallel. The JJ are based on YBa2Cu3O7–x epitaxial thin films deposited on SrTiO3 bicrystal substrates with misorientation angles of 24° and 36.8°. The epitaxial, c‐axis oriented YBa2Cu3O7–x films were grown “in situ” by a high oxygen pressure dc sputtering technique. For the fabrication of the superconductor loop a photolithographic method and a non‐aqueous chemical etching were used. The superconducting properties of the superconductor loops were analyzed by measuring the current–voltage characteristics. The magnetic field dependence of the critical current Ic(B) and the I–V curves under microwave irradiation showed weak‐link Josephson behavior. The dependence of Ic(B) shows an interference pattern due to the phase differences across the both junctions.
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