Blocking of valence fluctuations in europium oxynitrides

¹⁵¹Eu Mössbauer spectra of three compounds in the series EuO_1-xN_x with x = 0.05, 0.15 and 0.25 show well-resolved Eu²⁺ and Eu³⁺ absorbtion lines. The proportion of Eu³⁺ is just x. There is no evidence for electron hopping. Eu²⁺ appears to be unstable in environments with more than two nitrogen neighbours.     

Magnetic field effect on autocatalysis: Ag and Cu in concentrated nitric acid

The partial suppression of corrosion of Ag and Cu in concentrated nitric acid solution by a magnetic field of up to 5 T was studied. The corrosion current density of these metals was found to diminish with magnetic field and rotation speed in a rotating disk electrode experiment. The suppression of corrosion is associated with removal of the catalyst HNO(2) from the electrode and passivation of the electrode surface. The Lorentz force was identified as the driving force responsible for the partial suppression of corrosion. A model based on the partial areas associated with active and passive regions on Ag and Cu electrodes is introduced to explain the dependence of the current density on the applied magnetic field.     

Identification of a set of genes showing regionally enriched expression in the mouse brain

Background

We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.

Results

Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.

Conclusion

Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex.     

Mössbauer study of europium in fluorozirconate glass

¹⁵¹Eu Mössbauer spectra of fluorozirconate glasses of nominal composition 0.61 ZrF₄ · (0.32 ? x) BaF₂ · x EuF₂ · 0.07 ThF₄ with x = 0.10 and 0.20 show that Eu²⁺ is present in sites with isomer shifts in the range ?15.5 to ?12.9 mm/s, corresponding to EuF bond lengths of 2.3–2.8 Å and a coordination number ranging from 8 to 12. The glasses contain a minor amount (～10%) of Eu³⁺ in well-defined sites. Effective Debye temperatures deduced from the recoilless fractions for the two ions are θ_D²⁺ = 145 K and θ_D³⁺ = 261 K. The differences in coordination and bonding indicate that trivalent eurpoium is a network former, whereas the divalent ions are network modifiers.     

The magnetic concentration gradient force—Is it real?

There are suggestions in the electrochemical literature that a body force F _∇c acts when an electrolyte with a non-uniform concentration c of paramagnetic ions is subject to a uniform magnetic field. We demonstrate, experimentally and theoretically, that no such magnetic body force exists, to first order. A second-order correction associated with the demagnetizing field does lead to a very small concentration-dependent body force, which is not expected to produce any observable effect in electrochemistry. Contribution to special issue on Magnetic field effects in Electrochemistry.

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Thin films of semiconducting lithium ferrite produced by pulsed laser deposition

Thin films of lithium ferrite (Li_0.5Fe_2.5O₄) have been deposited on (0 0 1) Al₂O₃ by pulsed laser deposition, with substrate deposition temperatures ranging between 500 and 800 °C, and oxygen pressures between 1 × 10⁻¹ and 4 × 10⁻⁷ mbar. X-ray diffraction shows that films grow with a (1 1 1) orientation. Conversion electron Mössbauer spectra for the high-pressure films show a single sextet with a hyperfine field of 49 T, while the low-pressure films show two sextets with hyperfine fields of 47 and 49 T. The spectra also reveal paramagnetic ferric iron in both types of films. Magnetization measurements of the films show a saturation magnetization of between 1.7 and 3.1μ_B per formula unit and a coercivity of between 10 and 44 mT. The films prepared under the lower oxygen pressures are semiconducting with resistivities of 2 × 10⁻² to 8 × 10⁻² Ω cm. They exhibit an anomalous Hall effect with p-type conduction at 175 K.     

Electrochemical noise analysis of the effects of a magnetic field on cathodic hydrogen evolution

The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm^?2. A 1/f² variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force.     

Fabrication and characterization of electrodeposited Co1−xCrx nanowires

Co_1−xCr_x   alloy nanowires with 0.01<x<0.93$0.01<x<0.93$ were fabricated by electrodeposition in a porous alumina membrane from an electrolyte containing Co and Cr ions. The composition, structure and magnetic properties of the nanowires have been characterized. Cobalt-rich nanowires were electrodeposited at a potential of −1.0 V relative to Ag/AgCl and chromium-rich nanowires were deposited beyond −3.5 V. The optimized processing conditions include hydrogen annealing to give hysteresis loops for the Co₈₀Cr₂₀ nanowires with coercivity of up to 200 mT and squareness of up to 0.95. Magnetization of the Co₈₀Cr₂₀ nanowire is 77 A m² kg⁻¹ and the energy product of the arrays is 35 kJ m⁻³.     

An57Fe Mössbauer study of rare-earth intermetallic compounds R(Fe11Ti)

⁵⁷Fe Mössbauer spectra are reported for the ThMn₁₂ structure series of intermetallic compounds R(Fe₁₁Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient α_J of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe₁₁Ti) compound, which may find applications as a permanent magnet.