Pressure and field induced magnetic order in the spin liquid Tb2Ti2O7 as studied by single crystal neutron diffraction

We have studied the spin liquid Tb2Ti2O7 by single crystal neutron diffraction under high pressure up to 2.8 GPa, together with uniaxial stress, down to 0.1 K, in zero and high magnetic fields up to 7 T. In zero magnetic field, a long-range ordered antiferromagnetic structure is induced by pressure. The Néel temperature and ordered magnetic moment can be tuned by the anisotropic pressure component. Under magnetic field, the antiferromagnetic structure transforms into a canted ferromagnetic one at 0.6 T. Spin canting persists even at 7 T. The magnetic phase diagram under pressure shows a strong increase of the Néel temperature with the field.     

Single-crystal neutron diffraction under high pressures: valence instabilities in Tm monochalcogenides

New high-pressure devices based on the use of sapphire anvils now allow single-crystal neutron diffraction experiments to be performed up to P=8–10 GPa. After giving a brief overview of the technique, we present its application to the study of pressure-induced valence instabilities in Tm monochalcogenides (TmX, X: S, Se, Te). A variety of new magnetic phases have been characterized, yielding a consistent picture of the evolution of magnetism through the series. The results indicate a striking interplay between magnetic order taking place at low temperature and different types of electronic ground states (classical semiconductor, narrow-gap Kondo insulator, metallic Kondo lattice, etc.) inferred from the transport properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Search for effects beyond the born approximation in polarization transfer observables in e(over→)p elastic scattering

Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, G(E)/G(M), obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic H(e[over →],e(')p[over →]) reaction for three different beam energies at a Q(2)=2.5 GeV(2), spanning a wide range of the kinematic parameter ε. The ratio R, which equals μ(p)G(E)/G(M) in the Born approximation, is found to be independent of ε at the 1.5% level. The ε dependence of the longitudinal polarization transfer component P(?) shows an enhancement of (2.3±0.6)% relative to the Born approximation at large ε.     

Plasma-assisted deposition of a three-layer structure by vacuum andgas arcs

The durability and adhesion of thin coatings often depends on the structure and properties of the layer intermediate between the coating and the substrate, especially in the case where the layer and the substrate are highly different in microhardness. With a vacuum arc and a hot-cathode arc, a process has been arranged which involves cleaning of the surface, nitration of the article, and deposition of a coating. As a result, a three-layer composition has been produced which consists of a TiN layer of thickness up to 5 μm and microhardness 20 GPa, an intermediate Fe₄N layer of thickness up to 8 μm and microhardness 7.5 GPa, and a nitrated layer of thickness up to 100 μm with a gradually varying microhardness. With the TiN layer showing high adhesion, the coating has a durability three of four times greater than that of a coating produced with the use of a conventional technology     

Unusual thermal solid-phase rearrangement of 2-allylthio- and 2-allylselenodihydropyridines

A previously unreported thermal solid-phase migration of the allyl group was found for 2-allylthio- and 2-allylselenodihydropyridines, leading to 3-allyl-3-cyano-3,4-dihydropyridine-2(1H)-thiones and -selenones. Analysis of the crystal structures did not indicate whether the solid-phase reaction, which is probably general in nature, is intra- or intermolecular.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 521–523, February, 1991.     

Analysis method for apodised grating structures

A modified method of lines (MoL) technique is presented for calculating the reflection characteristies of apodised fibre gratings. To demonstrate the technique, reflection spectra of fibre gratings with triangular and diamond apodisation profiles were calculated showing significant side-lobe suppression. MoL can accurately calculate not only average power but also field and phase distribution across reflected waves. It is shown that the phase of the reflected light is maximally affected at the edge of the grating stopband.     

Spectral density function approach to homogenization of binary mixtures

The effective permittivity of binary mixtures having the spectral density function of the β distribution form is considered. Some particular cases such as low-concentration limit, weak and high dielectric contrast limit are considered in more detail. Finally, the validity of the approach for some microgeometries is supported by its good agreement with independent methods.     

Epoxy Composites Modified with Polyvinylidene Fluoride

Microheterogeneous structure and morphology of epoxy-based polymeric composites modified with polyvinylidene fluoride were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 634–638.Original Russian Text Copyright © 2005 by Vilenskii, Gritsai, Shtompel’, Goncharenko.