Colossal magnetoresistance of the inhomogeneous ferromagnetic semiconductor HgCr<Subscript>2</Subscript>Se<Subscript>4</Subscript>

A new method is described for attaining high magnetoresistance in inhomogeneous magnetic materials, which makes use of the formation of a depleted layer and a contact potential difference at the interface separating two semiconductors with different Fermi levels and the magnetic-field-induced variation in the contact potential difference and thickness of the interface layer. The proposed model of the magnetoresistive structure is realized on the basis of the HgCr₂Se₄ magnetic semiconductor. Layers of n-HgCr₂Se₄ up to a few tens of microns thick were prepared on the surface of p-HgCr₂Se₄ bulk single crystals by the diffusion technique. Application of a magnetic field stimulated in the structures a strong (by a factor of more than 200) increase of the current flowing through the n-layer.     

Propagation of picosecond transverse acoustic pulses in a kramers doublet system

Propagation of extremely short transverse-strain pulses is studied in a low-temperature crystal containing paramagnetic impurities with an effective spin S = 1/2 in Voigt geometry. It is shown that various types of acoustic solitons can form due to the spin-acoustic interaction between elastic-field components.     

New Adamantane Derivatives with NO-Generating Fragment

An approach to the synthesis of adamantane derivatives with NO-generating fragment containing nitroxy group has been developed. 1-Aminoadamantane, memantine, and adamantanecarboxylic acid have been used as initial compounds. The prepared compounds have shown ability to generate nitric oxide in a system mimicking biological reactions of nitro group reduction.     

Determination of the concentration profile of interfaces in multilayered nanostructures according to the angular dependence of X-ray photoelectron spectra: A new approach

The possibility of determining the concentration profile of interfaces in multilayered nanoheterostructures according to the data of the angular dependence of X-ray photoelectron spectra was shown. To solve this ill-posed inverse problem, we used Tikhonov’s regularization method with iterative refinement. To determine the optimum parameter of regularization, we used the L curve technique. The programs used for this study allowed high accuracy of calculations. All this made it possible to obtain information about the distribution of atoms of a definite sort with a resolution of 0.1–0.15 nm in depth. The results of numerical simulation of XPS spectra are given for a three-layered Cr/Fe structure. Solving the inverse problem for the initial data distorted by the statistical noise afforded a concentration distribution over depth for Cr and Fe atoms. The stability of the solution against experimental errors was determined.     

Influence of π stacking on the magnetic properties of the copper(II) complex with 6-phenyl-3-(2-pyridyl)-5-trifluoroacetylmethylidene-4,5-dihydro-1,2,4-triazine

The new N,N,O-ligand 6-phenyl-3-(2-pyridyl)-5-(trifluoroacetylmethylidene)-4,5-dihydro-1,2,4-triazine (L) was synthesized, and its complex with Cu^II was prepared. The structure of the complex was established by X-ray diffraction. Magnetic measurements and ESR studies were carried out. Ab initio calculations of the electronic structure, exchange interactions, and the effective magnetic moment were performed. The intrastack polarization effect between the π states of 1,2,4-triazine and the d states of copper was revealed and numerically validated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 549–554, March, 2008.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Equilibrium adsorption of a cyclopentane—benzene vapor mixture on active carbon

The data on adsorption of cyclopentane, benzene, and their mixture on active carbon were analyzed by the statistical thermodynamic model. A method to describe the state of a binary mixture in single micropores was offered. A substantial negative deviation from Raoult's law predicted by the concept of an ideal adsorption solution is a consequence of a decrease in the excessive Helmholtz energy brought about by progressive filling when values of the excessive energy are positive over a wide range of adsorption. The excessive values found for the entropy and internal energy of a mixture of molecules in a single micropore are negative due to the heterogeneity of the adsorption field. The approach suggested adequately describes the experimental data and can be used for the determination of differential heats of adsorption. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1070–1076, June, 1999.     

Nonlinear resonance between a soliton and Josephson plasma waves: experiment and theory

Resonant interaction of a soliton (Josephson fluxon) with its self-generated Josephson plasma waves is studied experimentally, numerically, and analytically. An externally applied magnetic field H forms a cos-like potential relief for the soliton in the annular junction. Soliton motion under the influence of the bias current leads to an emission of plasma waves, which gives rise to a resonance at a certain soliton velocity. This resonance on the current–voltage characteristics shows a clear backbending accompanied by a negative differential resistance. Our analysis quantitatively explains the observed effect.