P. K. Gallagher

Studies of oxygen-deficient Ba2YCu3O7−δ and superconductivity Bi(Pb)SrCaCuO

Abstract Ambient temperature measurements of the crystallographic cell parameters for oxygen deficient Ba 2 YCu 3 O 7−δ prepared by gettered annealing indicate the presence of microscopic differences in the oxygen configuration at fixed δ dependent on annealing temperature. The loss of superconductivity with increasing oxygen deficiency is shown to be due to a step-like increase in length of the plane copper-apical oxygen bond, and not to the orthorhombic to tetragonal transition. The crystal structure of the 84K superconductor Bi 2 Sr 2 CaCu 2 O 8+δ is described, as is the stabilization of 110K superconductivity via partial Pb/Bi substitution with long time annealing.

Versatile new metalorganic process for preparing superconducting thin films

A new technique for producing thin films of the high‐temperature perovskite superconductors, LnBa2Cu3O7−x, where Ln represents a rare‐earth element, using spin‐on metalorganic precursors is described. Pyrolysis of the spin‐coated films, consisting of mixed metal (2‐ethyl hexanoates), leads to black films up to several microns thick whose degree of orientation is a function of the processing temperature and duration. Representative films of YBa2Cu3O7−x on MgO begin to exhibit orientation with the c axis perpendicular to the film plane at heat treatments above 900 °C. The superconducting behavior of a highly oriented film produced at 990 °C is characterized by Tc(onset)=89 K, Tc(R=0)=77 K, and Jc=103 A cm−2 at 65 K.

Laser‐initiated deposition reactions: Microchemistry in organogold polymer films

Micron‐sized gold features have been produced by the cw Ar+ laser‐initiated decomposition of thin organogold polymer films. These features may exhibit pronounced periodic structure under a wide variety of experimental conditions, resulting from propagation of the reaction front ahead of the laser by the heat of reaction associated with the chemical transformation. Gold features formed by irradiation of gold chloride‐doped polymer films further demonstrate these thermal effects. Thermoanalytical studies provide pertinent data for selection of suitable precursor materials.

dc magnetron- and diode-sputtered polycrystalline Fe and amorphous Tb(FeCo) films: Morphology and magnetic properties

We have prepared polycrystalline Fe and amorphous Tb(FeCo) films using both dc diode‐ and magnetron‐sputtering techniques. Magnetic properties and aging characteristics of these films were measured by a vibrating sample magnetometer and an automatic torque magnetometer. Film morphologies were studied by transmission electron microscopy. The magnetic and aging characteristics are closely correlated to the film morphology. It was also found that different sputtering methods can be tailored to produce a similar film morphology. Among the sputtering parameters, the Ar pressure during deposition at room or lower temperature strongly influences the film morphology.

Initial permeability and intrinsic magnetic properties of polycrystalline MnZn‐ferrites

Permeability‐temperature curves of polycrystalline Mn0.41Zn0.42Fe2.16O4+x are interpreted in terms of theoretical models using the intrinsic magnetic properties as measured on a single crystal having virtually the same composition. The temperature dependence of μ can be fitted by the relation μ∼M/K1/2, as expected for cylindrical wall bulging, but the absolute value of μ is an order of magnitude below the theoretical value. Spherical bulging of a totally pinned wall is shown to yield a μ which is an order of magnitude smaller than the observed value due to the stiffness of the wall due to demagnetizing and anisotropy energy. It is suggested that a finite pinning of the walls at the grain boundary might explain our data. After annealing at pressures near the phase boundary, the theory does not fit the μ‐T curves. It is suggested that the bulk composition of the grains of the polycrystalline material is different from that of the single crystal due to preferential segregation at the grain boundary even befo...

Further Magnetic and Thermal Studies of Cast Rare‐Earth Permanent Magnets

Studies have been made of the effect of composition on the magnetic properties of arc‐cast alloys in the vicinity of Co3.5CuFe0.5Ce. The residual induction varies from 4000 to 6400 G with intrinsic coercive force values from approximately 5000 to 12 000 Oe. The maximum energy product values range from about 4 to 10×106 G Oe, the higher values generally associated with alloys of lower copper content. Freezing points of these alloys were determined for the first time using differential thermal analysis. Solidification occurs over a range of temperatures; initial freezing point decreases from 1177°C for a low copper alloy (Co3.94Cu0.5Fe0.56Ce) to 1124°C for a high copper alloy (Co2.63Cu2.0Fe0.36Ce). Several additional peaks were observed in the cooling curves after the initial freezing had occurred. These peaks are tentatively attributed to additional phases which are likely in view of the complexity of the Co–Ce and Cu–Ce binaries. The precipitation reaction at 400°C which was previously observed by metallo...

Cast Permanent Magnets of the Co5RE Type with Mixtures of Cerium and Samarium

Previous studies of the effect of composition on the magnetic properties of arc‐cast alloys in the vicinity of Co3.5CuFe0.5Ce yielded maximum energy products from 4 to 10×106 G Oe, residual inductions from 4000 to 6400 G, and intrinsic coercive forces from 5000 to 12 000 Oe. The partial substitution of samarium for cerium in alloys in this vicinity results in an improvement in permanent magnet properties, with maximum energy products from 4.6 to 12.3×106 G Oe, residual inductions 4300 to 7150 G, and intrinsic coercive forces from 4000 to 13 400 Oe. Freezing points of these alloys were determined using differential thermal analysis. The dependence of magnetic saturation on temperature was determined for several of these alloys from room temperature to 1.5°K. The saturation increases gradually with decreasing temperature without anomaly. The temperature coefficient of saturation magnetization between 25° and −100°C was found to be 0.1%/°C for the alloy Co3.5CuFe0.5Ce, 0.06%/°C for the alloy Co3.5Cu1.35Fe0.4...

Structural characterization of boron nitride films

The microstructure of amorphous hydrogenated boron nitride films, with nominal composition B3N:H, is characterized with respect to hydrogen bonding and distribution by combined application of nuclear‐magnetic‐resonance (NMR) spectroscopy, electron‐spin‐resonance spectroscopy, and evolved gas analysis. Previous infrared studies on annealed films suggest that hydrogen is present in multiple configurations; qualitatively, low‐temperature anneals (∼600 °C) deplete N‐H moieties whereas B‐H configurations are depleted at higher temperatures (∼1050 °C). Gas analysis corroborates these results, showing H2 peaks at ∼570 and ∼950 °C. From an analysis of nuclear dipolar couplings extracted from the 1H NMR spectra, it is concluded that the hydrogen is essentially randomly distributed as monohydrides; other configurations, such as dihydrides and monohydride clusters, are estimated to be less than 20% total. Furthermore, the 1H NMR spectra show no evidence of molecular H2 trapped in the films. In a film exposed to a hi...

Time and temperature dependences of phosphorus evolution from InP

Indium phosphide decomposes evolving phosphorus at temperatures below 360 °C in vacuum. Hence, heating in this range during processing epitaxial InGaAs films on InP substrates may lead to surface contamination of the active layer by phosphorus. This contamination can be minimized at elevated temperatures by initially depositing a passivating layer over the exposed parts of the substrate and/or active film well below the decomposition range of the substrate (e.g., at 250 °C) and then sintering the film directly or while continuing deposition at a higher temperature. The vapor pressure of phosphorus evolved from InP increases by an order of magnitude for each 45 °C increase in temperature.

Magnetic anisotropy in dc diode getter sputtered GdCo films—How important is the argon content in the films?

Amorphous magnetic GdCo films were prepared by a dc diode getter sputtering technique with no bias field applied to the substrate during the film growth. Films (type I) obtained using 1.0 kV and 60 mTorr Ar during the sputtering show perpendicular anisotropy with Keffu =1.5×105 erg/cm3. Films (type II) deposited at 2.0 kV and 28 mTorr Ar exhibit magnetic isotropy with Kinu≊0. However, the actual argon content in the type II films is three times of that in the type I films. Nevertheless, the argon impurity in both the type I and type II films is ≤1.0 at. %, which is far less than those obtained in the biased rf diode sputtered GdCo films. Also, the distribution of argon is uniform in the film as observed from the Rutherford backscattering spectrometry.