The spin turning in ferromagnetic Gd studied by positive muons

We have studied the muon precession frequency in a ferromagnetic single crystal of Gd metal. The overall features of our findings are compatible with earlier results on polycrystalline material. In the temperature region between 245 and 220 K where the Gd magnetization starts to turn away from the c-axis, we observe an increase in the muon depolarization rate, and a complex precession signal which can be separated into two frequency components meaning that spin turning does not occur simultaneously in different parts of the sample (domains). From these more detailed data follows that previously obtained values forB _fc andB _dip can not both be correct. Two explanations for our new result are possible: EitherB _fc undergoes a change around 230 K which is directly coupled to the spin turning angle, or the value of the dipolar field contribution used in the earlier evaluation is too low. This imposes some uncertainty as to the value of the angle at the onset of spin turning derived fromSR frequencies.     

Low temperature magnetic ordering of a series of structurally characterized chloroferrates

Iron-57 Mössbauer spectroscopic results for a new series of related chloroferrate salts of complex ammonium cations are presented. In particular, spectra of materials based on FeCl ₄ ^– , FeCl ₅ ^2– , FeCl ₆ ^– , [FeCl₅(H₂O)]^2–, and [FeCl₅(CH₃OH)]^2– anions are discussed relative to the systematics of their isomer shifts, coordination numbers, and low temperature 3D critical ordering temperatures. The following specific systems have been studied by Mössbauer spectroscopy and definitively characterized by single-crystal X-ray analysis: [CH₃NH ₃ ⁺ ]₄[FeCl₆]^3–[Cl^–](A), [Me₂N(-CH₂CH₂)₂NMe ₂ ⁺ ][FeCl ₅ ^2– ] (B), [H₃NCH₂CH₂NH ₃ ²⁺ ][FeCl₅·H₂O^2–], (C), and [NH₃(CH₂)₆NH ₃ ²⁺ ]₄[(FeCl ₆ ^3– )(FeCl ₄ ^– )ClCl ₄ ^– ] (D). The spectral data for these complexes are considered in the light of results of previous studies for systems such as [K₂FeCl₅·H₂O], [Co(NH₃)₆][FeCl₆], diamethyltriethylenediammoniumpentachloroferrate (E), and the related [FeCl₅·CH₃OH]^2– salt (F). The critical 3D ordering temperatures are 1.45, 6.80, 3.45, and 1.22K forA, B, C, andD, respectively.     

Evaluation of electric hyperfine interactions inAuFe andCrFe

A detailed analysis of room temperature⁵⁷Fe Mössbauer spectra ofAuFe (5 at.% Fe) andCrFe (5, 10 at.% Fe) samples is presented. The deviation from Lorentzian line shape observed in the spectra indicates both thickness effects and structural disorder in these systems. The thickness effect has been taken into account using a new fitting technique that solves the transmission integral numerically rather than relying on the thin absorber approximation. The present results and analyses using both the thin absorber approximation and the full transmission integral methods on these alloy systems are compared with earlier results obtained on these alloy systems using only the thin absorber approximation.     

Sodium self-diffusion coefficient in sodium silicate glass by quasielastic neutron scattering

Using pulsed neutrons of 19.8 Å wavelength a quasielastic line broadening as low as 0.03 eV (FWHM) has been observed due to Na⁺ diffusion in the glass Na₂O·2SiO₂. From the linewidths a Na⁺ self-diffusion coefficient of 3.1·10^–8 cm²/s at 420°C was obtained in excellent agreement with the diffusion coefficient determined for the same sample batch using²²Na radioactive tracers. The experimental Q dependence of the quasielasic linewidths gives a hint for deviations from a purely random walk in an ionic glass.     

Gravity and CP violation

The non-conservation of CP symmetry in the decay of neutralK mesons was discovered almost three decades ago. The origin of this unique phenomenon is still not well understood. There have been attempts to link it with energy splitting of theK and in the earth's gravitational field. In this essay we examine these attempts critically. A more natural way in which a gravitational field can couple asymmetrically to the system is through torsion, which coupling to isospin can, in addition to parity violation, also give rise to a C violation. The magnitude of this effect is estimated in the vicinity of a kaon and found to give a CP-violating parameter of the right value. Moreover, it is predicted that the CP violating parameter for the new system is much smaller 10^–6. Implications for baryogenesis in the early universe is also studied. In this paper we work not with the Newtonian gravitational constantG but with a torsion coupling constant, which is energy-dependent and can be related to the Fermi weak interaction constant.     

Call for papers

Time-resolved vibrational spectroscopy

Call for papers     

Separation and implantation of relativistic86Kr-fragments at the FrS; half-life measurement by ion-β time-correlations

Neutron-rich Co and Fe isotopes produced by⁸⁶Kr projectile fragmentation at 500 MeV/u were separated and identified using the fragment separator (FrS) in a bunched energy mode.⁶⁶Co and⁶⁵Fe ions were selectively implanted in a double PIN-diode array where the-decay signals were measured. The half-lives were deduced from time correlations between implantation and-decay signals. The remeasurement of the⁶⁶Co half-life confirms the isotope identification. The value of the⁶⁵Fe half-life was found to be 0.45±0.15 s.     

High-resolution laser spectroscopy on H2 at 97–98 nm

A narrowband tunable eXtreme UltraViolet (XUV) laser source is used for a high resolution study of the Lyman (B ¹ _u ⁺ X ¹ _g ⁺ ) band system of molecular hydrogen. Seven rotational transitions of two vibrational bands, (10,0) and (11,0), in the wavelength range from 97.2–98.3 nm have been investigated for the first time under sub-Doppler molecular beam conditions. A calibration procedure using the I₂ standard in the visible yielded an absolute frequency accuracy of 0.02 cm^–1. The obtained H₂ transition frequencies provide a calibration standard in the extreme ultraviolet wavelength region.     

Pulsed photothermal laser deflection for low-level smoke and NO2 measurements in engine exhausts

Pulsed Photothermal Laser Deflection (PLD) is developed to make temporally and spatially resolved measurements of NO₂ and smoke. The rapid response PLD signal is produced when a HeNe probe beam is deflected by a thermal lens produced by a pulsed XeCl-excimer laser pumped dye laser. The fast time response (30 ns) and good spatial resolution make the PLD method a candidate for future in situ measurements in turbulent engine exhausts. The PLD signals, measured in a sample cell, exhibit a linear response for NO₂ concentrations from 3 ppm to 208 ppm and for smoke concentrations from 0.3 mg/m³ to 10 mg/m³. With a low pulse energy of 4 mJ, single-shot PLD measurements in a sample cell have accuracies of ± 14 ppm for NO₂ indicating accuracies of ±0.7 mg/m³ for smoke. With increased pulse energy and multi-shot averaging, sensitivities of ± 0.4 ppm of NO₂ or ± 20 µg/m³ of smoke are expected.     

Gas-discharge XeF* (B→X) laser with high specific output energy

The discharge characteristics of the XeF* (BX) laser are investigated. The NF₃ and Xe partial pressure of the laser gas mixture and the total gas pressure have been varied. A highest specific output energy of 4.7 J/l with an efficiency of 0.5% was obtained from a X-ray preionized Ne/Xe/NF₃ gas mixture at 6 bar with single-pulse excitation through a multichannel spark gap.