John T. Mcdevitt

Intra- versus intergranular low-field magnetoresistance of Sr2FeMoO6 thin films

Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited on LaAlO3 and SrTiO3 (001) substrates. Comparison of their transport and magnetic properties with those of polycrystalline ceramic samples shows a metallic versus semiconductor temperature dependence and a saturation magnetization Ms at 10 K of 3.2 μB/f.u. in the film as against 3.0 for a tetragonal polycrystalline sample. However, the Curie temperature TC≈389 K is reduced from 415 K found for the tetragonal ceramic, which lowers Ms at 300 K in the thin films to 2.0 μB/f.u. compared to 2.2 μB/f.u. in the ceramics. A Wheatstone bridge arrangement straddling a bicrystal boundary has been used to verify that spin-dependent electron transfer through a grain boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC.

Multi-shell microspheres with integrated chomatographic and detection layers for use in array sensors

The development of miniaturized chromatographic systems localized within individual polymer microspheres and their incorporation into a bead-based cross-reactive sensor array platform is reported. The integrated chromatographic and detection concept is based on the creation of distinct functional layers within the microspheres. In this first example of the new methodology, complexing ligands have been selectively immobilized to create separation layers harboring an affinity for various metal cations. Additionally, a broadly responsive compleximetric dye is used to yield the detection layers that exhibit optical responses in the presence of a wide range of metal cations. Information concerning the identities and concentrations of solution-dissolved metal cations can be drawn from the temporal properties of the beads optical responses. Varying the nature of the ligand in the separation shell yields a collection of cross-reactive sensing elements well-suited for use in array-based micrototal analysis systems. Accordingly, such beads have been incorporated into the Electronic Taste Chip platform and used for discriminating among aqueous metal cation solutions.

Effect of tolerance factor and local distortion on magnetic properties of the perovskite manganites

The substitutions of rare earths for La on the magnetic properties of the perovskites La0.7−xRxA0.3MnO3 (0<x<0.7), R=Pr or Gd and A=Ca, Sr, or Ba have shown that small substitution of Pr slightly increases the coercive field Hc and magnetization M, and strongly improves the magnetoresistance (MR) while lowering Tc. On the other hand, the substitution of Gd lowers Hc, M and Tc, however, increases MR of the system La0.7−xGdxSr0.3MnO3 at temperature <Tc. Large differences in the A-site ionic radii rA of the AMnO3 perovskites proved detrimental. The optimal composition has been discussed for the half-metallic ferromagnet of a spin-switch device based on the manganese oxides.

Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films

Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited or LaAlO3 and SrTiO3 (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr2FeMoO6 was obtained in 100 mTorr 99.999% Ar gas at 825u200a°C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization Ms at 10 K of 3.2μB/f.u. However, the Curie temperature TC≈380u200aK was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers Ms at 300 K in the thin films to 1.5μB/f.u. compared to 2.2μB/f.u. in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC.

serum biomarker release patterns following alcohol septal ablation for treatment of hypertrophic cardiomyopathy

Alcohol septal ablation (ASA) is employed to relieve the pressure gradient associated with symptomatic hypertrophic cardiomyopathy. Serum concentrations of cardiac troponin I, creatine kinase MB band, brain natriuretic protein, matrix metalloproteinase-9, myoglobin, C-reactive protein, tumor necrosis factor-alpha, soluble CD40 ligand, interleukin-6, adiponectin, interleukin-1β, myeloperoxidase, and soluble intercellular adhesion molecule-1 were determined at baseline and at 8, 16, 24, and 48 hours in patients with hypertrophic cardiomyopathy presenting for ASA. Comparisons were made with 107 healthy control subjects. Sixteen hours following ASA, serum levels rose over 800-fold for cardiac troponin I, 70-fold for creatine kinase MB band, and 11-fold for myoglobin (P,0.001). C-reactive protein and interleukin-6 both rose slowly and became significantly elevated at 16 and 48 hours, respectively. Matrix metalloprotease-9 rapidly increased two-fold at 8 hours, but returned to baseline thereafter. Other biomarkers evaluated either trended downward or showed little change from baseline. Among the ASA patients, baseline serum concentration of all biomarkers, except for matrix metalloproteinase-9, soluble intercellular adhesion molecule-1, and myeloperoxidase, were elevated in the ASA group compared with the controls. These findings suggest that hypertrophic cardiomyopathy is a proinflammatory and prothrombotic state. The time-dependent changes in these biomarkers suggest they may be useful in predicting the success of ASA and could potentially offer insight

Improved J/sub c/ of bilayer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film structures

Critical-current (J/sub c/) measurements for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), Gd/sub 0.6/Ca/sub 0.4/Ba/sub 1.6/La/sub 0.4/Cu/sub 3/O/sub 7-/spl delta// (TX-GBCO) and TX-GBCO/YBCO bilayers were performed with transport measurements at different applied magnetic fields. The film samples were prepared by pulsed laser deposition and patterned as microbridges. The highest J/sub c/ (1.5/spl times/10/sup 6/ A/cm/sup 2/) at 75 K in 5 Tesla (Hllab) was observed for TX-GBCO/YBCO bilayers, which showed a 40% increase in J/sub c/ over YBCO under the same conditions. The bilayer samples possess a T/sub c/ at 90 K and display superconducting properties similar to YBCO. A possible mechanisms for the high J/sub c/ of bilayer YBCO films is discussed. Development of these bilayer and multilayer structures represents a promising new direction to improve the superconducting properties of YBCO since the TX-GBCO layer provide both protection against corrosion and a significant improvement in J/sub c/.Critical-current (J c ) measurements for YBa 2 Cu 3 O 7-δ (YBCO), Gd 0.6 Ca 0.4 Ba 1.6 La 0.4 Cu 3 O 7-δ (TX-GBCO) and TX-GBCO/YBCO bilayers were performed with transport measurements at different applied magnetic fields. The film samples were prepared by pulsed laser deposition n and patterned as microbridges. The highest J c (1. 5 X 10 6 A/cm 2 ) at 75 K in 5 Tesla (Hllab) was observed for TX-GBCO/YBCO bilayers, which showed a 40 % increase in J c over YBCO under the same conditions. The bilayer samples possess a T c at 90 K and display superconducting properties similar to YBCO. A possible mechanisms for the high J c of bilayer YBCO films is discussed. Development of these bilayer and multilayer structures represents a promising new direction to improve the superconducting properties of YBCO since the TX-GBCO layer provide both protection against corrosion and a significant improvement in J c .

Development of ramp-edge SNS junctions using highly stable normal-metal barrier materials

By using a cation-modified and corrosion-resistant compound of (Pr/sub y/Gd/sub 0.6-y/)Ca/sub 0.4/Ba/sub 1.6/La/sub 0.4/Cu/sub 3/O/sub 7/ (y=0.4, 0.5, and 0.6) as normal-metal barrier materials, high-temperature superconducting Josephson junctions have been fabricated in a ramp-edge superconductor/normal-metal/superconductor (SNS) configuration. We have tuned the Pr substitution level in order to achieve the optimal electrical resistivity of the barrier layer for high-performance SNS junctions. The junctions fabricated with these normal-metal barriers show well-defined RSJ-like current vs voltage characteristics at liquid-nitrogen temperature. The junction performance is mainly controlled by the N-layer instead of the interface. We have also fabricated dc superconducting quantum interference devices based on ramp-edge SNS technology with these normal-metal barriers. The ratio of peak-to-peak voltage modulation of the superconducting quantum interference devices to the I/sub c/R/sub n/ product is more than 30%.