FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction analysis, and magnetic measurements. Loading the templates with a Fe chloride and Pt chloride mixture followed by hydrogen reduction at 560 °C leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. Using a Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The length of the nanotubes is about 50 μm and their diameters range from about 150 to 220 nm, depending on the thickness of the template film and the pore diameter distribution. Reflecting the different magnetocrystalline anisotropies of the compounds, the coercivities range from 0.61 kOe for Fe3O4 to 20.9 kOe for FePt. The hysteresis is explained in terms of a tubular random-anisotropy model, which yields a diameter and anisotropy dependent transition from a curling-type mode (Fe3O4) to a localized mode (FePt).

We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria, Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data showed a two-log10 CFU reduction of bacteria when 2 x 10(2) cells were seeded on filter paper. Results showed > or = 3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 x 10(4)) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect > or = 6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min generated > or = 5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 x 10(5)); 7 min OAUGDP exposures were required to generate a > or = 3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.

We have investigated the pinning of vortices in high-J c films of polycrystalline MgB 2 , by studying the dependence of current density J on electric field E using both magnetic and transport methods. Precursor films of amorphous boron, deposited on sapphire substrates, were converted to 0.6 µm thick MgB 2 by post-annealing in the presence of Mg vapour at 890 • C for 1 h. In magnetic studies, a SQUID magnetometer was used conventionally to determine the induced current density by the Bean model. The decay of J with time t was determined unconventionally with the sample fixed in position, by monitoring the SQUID feedback voltage ∝J versus time. The logarithmic decay rate S = −d ln(J )/d ln(t) was found to be very low in the H-T phase space away from the irreversibility line. Complementary four-probe transport studies of E(J ) were analysed as a power law dependence of the form E ∝ J n and used to obtain the corresponding creep rate S = 1/(n − 1). Effective values for n approach and often significantly exceed 100. From these results, we estimate the effective energy U 0 for vortex pinning, as a function of magnetizing field H.

FePt and Fe 3 O 4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometry. Loading the templates with an Fe chloride and Pt chloride mixture, followed by hydrogen reduction at 560°C, leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. An Fe nitrate solution, thermally decomposed at 250°C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe 3 O 4 tubes. The versatility of the method indicates that materials with a wide range of parameters can be produced.

Fine grained polycrystalline samples of MgB 2 superconductor were synthesized from the elements to contain < 5 % of impurity phases, according to x-ray powder diffractometry. The superconductive transition was sharp with a midpoint T c = 38.5 K. The magnetization in the vortex state was studied as a function of applied field H , temperature T and time t. From the equilibrium magnetization, the London penetration depth was obtained. The supercurrent density J (T , H, t) in the vortex state (derived from the irreversible magnetization) decreases approximately linearly with T , in contrast to the quasi-exponential fall-off in high-T c superconductors. The current is highly stable in time, with normalized decay rates S = − d ln(J )/d ln(t) well below those in high-T c materials. These results are compared with those of other superconductors.

Oriented Fe1−xPtx nanoparticles have been formed in single-crystal Al2O3 host matrices by the sequential implantation of Fe and Pt ions followed by thermal annealing. For x in the range of ∼35–55 at. % Pt, these nanoparticles are in the chemically ordered tetragonal L10 structure of FePt and appear to be fully ordered. The nanoparticles are ferromagnetic, and the magnetic coercivity is a strong function of the alloy composition, reaching values in excess of 20 kOe for x∼45%. The crystallographic orientation and morphology of the nanoparticles are strongly dependent on the implantation conditions. Under certain implantation conditions, a buried amorphous layer can be formed in the Al2O3 matrix which crystallizes during annealing giving rise to the formation of an interconnected network of large FePt particles with a single orientation. Oriented nanoparticles of Fe3Pt and FePt3 were also synthesized. The Fe3Pt and FePt3 particles have the ordered, cubic L12 structure with an order parameter of 0.5–0.8; and these particles also exhibit ferromagnetic behavior. The magnetic and structural properties of the Fe1−xPtx nanoparticles are compared to and contrasted with those of nanoparticles of Fe and Pt in Al2O3 that were also formed by ion-beam synthesis. Evidence for Al incorporation into the nanoparticles is also presented.

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