Point-contact study of the heavy-fermion superconductor CeCoIn5

We have investigated the differential conductance spectra of the point contacts between the heavy-fermion superconductor CeCoIn₅ and Pt. Many of them show a double-maximum structure that indicates the superconducting energy gap Δ. The Δ values derived using Blonder-Tinkham-Klapwijk model, however, varies from 0.47 to 0.77 meV, and yet they are within the scatter of the reported values. The evolution of Δ below T_c is slow as compared with that of BCS gap probably reflecting the unconventional superconductivity in CeCoIn₅.     

Thermal stability of high concentration Fe-Ag and Fe-Cu alloys produced by vapor quenching

Mössbauer effect measurements were carried out for sputtered fcc Fe-Ag and Fe-Cu alloys annealed at various temperatures. At temperatures higher than 300 °C, the metastable fcc phases decompose by removing saturated Fe atoms. During the phase separation processes, the ejected Fe atoms form clusters, which initially have a fcc structure and transform to bcc particles as their sizes grow beyond a critical value.     

Mössbauer spectra and electronic structure of nonequilibrium Fe-Cu alloys produced by vapor quenching

Mössbauer spectra have been observed for nonequilibrium bcc and fcc Fe–Cu alloys sputter-deposited at several Ar gas pressures,P _Ar. These alloys are ferromagnetic at low temperatures and show sextet spectra. The fcc alloys which are paramagnetic at 290 K show asymmetric doublet spectra, indicating no serious segregation. In the alloys deposited at highP _Ar, the weak intensity ratios of the second and fifth lines of the sextet indicate a tendency of perpendicular magnetic anisotropy, while a large magnetic hyperfine field component of about 40 MA/m (500 kOe) at 4.2 K and a large quadrupole splitting component of about 0.7 mm/s at 290 K imply CuFeO₂ formation. The nonequilibrium, bcc and fcc Fe–Cu, alloys are maintained below 500 K and the phase separation is detected above 550 K. X-ray photoemission spectroscopy studies of these alloys reveals individual Fe- and Cu-d bands. The concentration dependence of peak intensities and peak positions indicate that Fe and Cu electronically intermix.     

Vertically aligned carbon nanotubes from natural precursors by spray pyrolysis method and their field electron emission properties

Vertically aligned carbon nanotubes have been synthesized from botanical hydrocarbons: Turpentine oil and Eucalyptus oil on Si(100) substrate using Fe catalyst by simple spray pyrolysis method at 700°C and at atmospheric pressure. The as-grown carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Raman spectroscopy. It was observed that nanotubes grown from turpentine oil have better degree of graphitization and field emission performance than eucalyptus oil grown carbon nanotubes. The turpentine oil and eucalyptus oil grown carbon nanotubes indicated that the turn-on field of about 1.7 and 1.93 V/μm, respectively, at 10 μA/cm². The threshold field was observed to be about 2.13 and 2.9 V/μm at 1 mA/cm² of nanotubes grown from turpentine oil and eucalyptus oil respectively. Moreover, turpentine oil grown carbon nanotubes show higher current density in relative to eucalyptus oil grown carbon nanotubes. The maximum current density of 15.3 mA/cm² was obtained for ∼3 V/μm corresponding to the nanotubes grown from turpentine oil. The improved field emission performance was attributed to the enhanced crystallinity, fewer defects, and greater length of turpentine oil grown carbon nanotubes.     

Formation of new metastable transition metal alloys by combination of mechanical alloying and chemical leaching

The leaching of Al atoms from B2 structures of mechanically alloyed Ni and Co aluminides led to the formation of metastable B2 Ni and Co. B2 Ni is strong paramagnet not stable above 470 K. The magnetic moment of Co atom in ferromagnetic B2 phase is smaller than in fcc one. B2 Ni demonstrates high catalytic activity in hydrogenation of organic compounds.     

Fe-Pt invar alloys—homogeneous strong ferromagnets

The thermal expansion and magnetic properties of Fe-Pt Invar alloys in both ordered and disordered states indicate that inhomogeneities play no essential role in determining large magnetovolume effects in Fe-Pt alloys. On the other hand, the concentration dependence of the magnetization, the hyperfine field at Fe nuclei and other related properties clearly show the strong ferromagnetism in Fe-Pt Invar alloys. Comparing the Invar behaviour found in Fe-Pt alloys with that in Fe-Ni alloys, it has been concluded that the so-called Invar effect generally consists of two types of anomalies. One is the essential effect, i.e., the large magnetovolume effect arising from the 3d band polarization and the other is the secondary or additional effect manifested as various magnetic anomalies associated with heterogeneities or weak ferromagnetism.     

Neutron scattering study on dynamics of water molecules in MCM-41. 2. Determination of translational diffusion coefficient

Quasielastic neutron scattering (QENS) spectra of water-filled MCM-41 samples (pore diameters: 21.4 and 28.4 Angstrom) were measured over the temperature range 238-298 K and the momentum transfer range 0.31-0.99 A(-1) to investigate the dynamics of confined water molecules. The spectra, which consist mainly of contributions from the translational diffusion of water molecules, were analyzed by using the Lorentzian and the stretched exponential functions. Comparison of the fits indicated that the latter analysis is more reliable than the former one. The fraction of immobile water molecules located in the vicinity of the pore walls, which give an elastic component, was found to be 0.044-0.061 in both pores. The stretch exponent beta was determined as 0.66-0.80. It was shown that the translational diffusion of water molecules in the pores is decelerated by confinement and that the deceleration becomes marked with a decrease in pore size. The ratios of the translational diffusion coefficient D(T) of confined water to that of bulk water at room temperature were within a range of 0.47-0.63.     

Thickness dependence of magnetization in FeNi invar alloy film

The thickness dependence of magnetization of FeNi Invar alloy films was observed by means of small angle Lorentz electron diffraction. A remarkable reduction of magnetization at room temperature was observed for films with thickness below 400 Å. This may be ascribable to the instability of the ferromagnetic state in Fe-Ni Invar alloys.     

Vapor quenched Fe-Ti alloys: Formation of amorphous phase,and metastable Ti2Fe phase by aging

Mössbauer spectra were observed for amorphous Fe-Ti alloys produced by vapor quenching. The average values of the hyperfine field, the quadrupole splitting and the isomer shift vary gradually with increase in Ti concentration. After being annealed at 400°C for few hours, the amorphous phase is maintained around 33 at % Ti, while an intermediate phase, Ti₂Fe, appears around 67 at % Ti.     

Low polydispersed copper-sulfide nanocrystals derived from various Cu-alkyl amine complexes

Copper-sulfides, Cu2-xS nanocrystals (NCs) have been synthesized using the reaction between a Cu-alkyl amine complex and a sulfur/1-dodecanethiol. Here, 1-dodecanthiol plays an important role to reduce the reaction temperature of sulfuration. The Cu/S composition (the Cu-defect density) of Cu2-xS NCs depends on the stability of Cu-alkyl amine complex. XPS analyses reveal that the substance of Cu-defect is attributed to an introducing of Cu+2S2-2 species. There is a good correlation between an intensity of a near IR absorption peak and a Cu-defect density estimated by XPS analyses. These results demonstrate that optical properties of Cu2-xS NCs in a near IR region are tunable.