The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films

Temperature dependences of the magnetic moment have been measured in YBa_2Cu_3O_{7-\delta} thin films over a wide magnetic field range (5 <= H <= 10^4 Oe). In these films a paramagnetic signal known as the paramagnetic Meissner effect has been observed. The experimental data in the films, which have strong pinning and high critical current densities (J_c ~ 2 \times 10^6 A/cm^2 at 77 K), are quantitatively shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559 (1995)]. This finding indicates that the origin of the paramagnetic effect is ultimately associated with nucleation and inhomogeneous spatial redistribution of magnetic vortices in a sample which is cooled down in a magnetic field. It is also shown that the distribution of vortices is extremely sensitive to the interplay of film properties and the real experimental conditions of the measurements.Comment: RevTex, 8 figure

Synthesis, structure, and electrical behavior of Sr4Bi4Ti7O24

An n=7 Aurivillius phase, Sr4Bi4Ti7O24, with c=6.44 nm, was synthesized as an epitaxial (001)-oriented film. This phase and its purity were confirmed by x-ray diffraction and transmission electron microscopy. The material is ferroelectric, with a P-r=5.3 mu C/cm(2) oriented in the (001) plane and a paraelectric-to-ferroelectric transition temperature of T-C=324 K. Some indications of relaxorlike behavior are observed. Such behavior is out of character for Srn-1Bi2TinO3n+3 Aurivillius phases and is closer to the bulk behavior of doped SrTiO3, implying a spatial limit to the elastic interlayer interactions in these layered oxides. A finite-element solution to the interpretation of data from interdigitated capacitors on thin films is also described

Critical thickness of high structural quality SrTi03 films grown on orthorhombic (101) DySc03

Strained epitaxial SrTiO3 films were grown on orthorhombic (101) DyScO3 substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018 degrees). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700 degrees C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO3 films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3037216