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TbMnO3 thin films with different crystallographic orientations were deposited epitaxially on LaAlO3 [100] and SrTiO3 [100] single crystal substrates by using pulsed laser deposition. Magnetization measurements were performed along the [110], [-110], and [001] directions of the films. Obvious magnetic anisotropy and low temperature ferromagnetism were found. Transitions at T ∼ 10, 32, 120, and 125 K along different directions are observed. The susceptibility anomalies, remarkably anisotropic, are discussed on the frame of the domain wall and strain-induced distortion. Particularly, the lattice mismatch and the anisotropic thermal expansion between the films and substrates are likely responsible for the distortion behaviors. [ABSTRACT FROM AUTHOR]

Abstract: It is well-known that there is a relatively small temperature window for the growth of epitaxial and c-axis oriented YBCO thin films by various methods. In this study, this window was more precisely examined for YBCO film growths by photo-assisted MOCVD. At specified total reactor pressure of 4.6torr, and specified respective partial pressures for the oxidizing agents, O2 and N2O at 1.7torr and 1.1torr, the film growths were tested at several substrate temperature (T s) points from 780°C to 864°C. The film growth time for each test was 3min. As to compositional purity, purity in c-axis orientation, and crystal structural quality of these tested films by using photo-assisted MOCVD technique, it was found that for the growth of purely c-axis oriented YBCO thin films with high crystalline quality, the appropriate growth temperature range (or “T s window”) was from about 800°C to 830°C, at relevant pressures as specified above. T c and J c of a typical YBCO film sample grown within this “T s window”, i.e., 810°C, were found as 90K and 1.32MA/cm2 (77K, 0Oe) respectively by magnetization measurements. It is noticeable that this film, and other purely c-axis oriented YBCO films are all single-crystal like and dense, with no SEM visible grain boundary or void. The causes of precipitates found on top surface of these c-axis oriented YBCO films are also discussed. [Copyright &y& Elsevier]

Abstract: Superconducting YBa2Cu3O7− x thin films were deposited on LaAlO3 (100) substrates by a photo-assisted metal-organic chemical vapor deposition (MOCVD) technique. In our experiment, growth temperature, chamber pressure and growth time were all fixed; the only process variable was the susceptor inclination angle (Φ) between the axis of gas inlet and the susceptor surface. It was found that the growth rate of YBCO films increases monotonically as Φ increases, whereas the superconducting critical current density (J c) has a maximum (1.2×106 A/cm2) near Φ =22.5°. The experimental results were found to be well correlated with the three-dimensional simulations of gas flow inside the MOCVD reactor, with Φ being the only process variable. [Copyright &y& Elsevier]