A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La(0.67)Ca(0.33)MnOx. Epitaxial films that are grown on LaAIO(3) substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and approximately 1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

Melt-textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle- or plate-shaped crystals preferentially aligned parallel to the a-b conduction plane. The new microstructure, which completely replaces the previous granular and random structure in the sintered precursor, exhibits dramatically improved transport Jc values at 77 K of ∼17 000 A/cm2 in zero field and ∼4000 A/cm2 at H=1 T (as compared to ∼500 and ∼1 A/cm2, respectively, for the as-sintered structure), with the severe field dependence of Jc (‘‘weak-link’’ problem) no longer evident in the new melt-textured material. The improvement in Jc is attributed to the combined effects of densification, alignment of crystals, and formation of cleaner grain boundaries. Microstructure and distribution of various phases present in the melt-textured material are discussed in relation to the superconducting properties.

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Preparation of superconducting BiSrCaCuO thin films by sequential electron beam evaporation and oxygen annealing Appl.

The object of this study was to screen a group of metal oxides as possible candidates for use as semitransparent mask materials. For this study, all masks were prepared by d‐c reactive sputtering onto glass. The uv‐visible spectra for the entire group of oxide films were recorded. The spectral characteristics desired for a photomask are (i) transmission of less than 1% in the region below 404 nm (for masking), and (ii) transmission of greater than 30% at 589 nm (for the see‐through characteristic). Because of inferior spectral absorption properties, the following systems were eliminated from further consideration: lead oxide‐silicon oxide, lead oxide‐germanium oxide, copper oxide, copper oxide‐vanadium oxide, molybdenum oxide, chromium oxide, uranium oxide, mercury oxide, and zinc oxide. Those systems which satisfied the spectral requirements were: iron oxide, vanadium oxide, nickel oxide, iron oxide‐nickel oxide, and iron oxide‐vanadium oxide. These materials were then further evaluated to assure etchability in solvents compatible with photoresist processsing and resistance to abrasion. These latter two properties will be discussed in greater detail in a forthcoming article. Considering only sputtered films, the 10 m/o (mole per cent) iron oxide‐90 m/o vanadium oxide is the most promising material based on these additional requirements.