Synthesis and magnetic and electrical study of Tm<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>S solid solutions

New antiferromagnetic semiconductor compounds Tm_xMn_1–xS (0 ≤ x ≤ 0.15) with an NaCl-type FCC lattice are synthesized, and their structural, magnetic, and electrical properties are investigated at temperatures of 80–1100 K in magnetic fields of up to 10 kOe. Anomalies in the temperature dependence of resistivity in the region of magnetic transition are observed. The activation energy of the synthesized compounds is found and shown to grow along with the concentration of a substitute.     

Mössbauer spectroscopy study of the EuO:Fe spintronic material

The states of iron and europium in the EuO:Fe composite spintronic material have been studied by means of room-temperature Mössbauer spectroscopy. In both cases, two sets of lines indicating the ferromagnetism and superparamagnetism of metallic iron nanoparticles in the composite and the appearance of a fraction of europium ions in the Eu³⁺ oxidation state in the matrix in addition to the main Eu²⁺ state have been observed in the respective spectra. In the europium case, the observation implies the possibility of a partial spin polarization of paramagnetic europium ions in Eu-Fe-O clusters and an increased specific magnetization of the composite.     

2‐Polyfluoroacylcycloalkanones in reactions with selected phosphorus(III) compounds

The reactivity of 2‐polyfluoroacylcycloalkanones and their O‐silylated derivatives towards phosphites and tris(trimethylsilyl)aminoiminophosphine has been investigated. From α‐polyfluoroalkyl substituted phosphonates, generated from tris(trimethylsilyl) phosphite and 1,3‐diketones, the respective phosphonic acids and their salts have been obtained. In one case, upon warming, a phosphonic acid underwent a ring closure to yield an oxaphospholene. 2‐Trifluoroacetylcycloalkanones and diethyl isocyanatophosphite furnished phosphoranes diastereospecifically, via addition of phosphorus at the trifluoroacetyl group and two additional heterocyclizations. Tris(trimethylsilyl)aminoiminophosphine formed very reactive trimethylsilylimino‐1,2λ⁵σ⁴‐phospholenes, which added hexafluoroacetone to give spirocyclic 1,3,2λ⁵σ⁵‐oxazaphosphetanes. The structures of the new compounds were determined by NMR spectroscopy and X‐ray single crystal analysis. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:97–107, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10001     

Lexicographic optima in the multicriteria discrete optimization problem

It is shown that any lexicographic optimum in vector optimization problems on a finite set of admissible solutions can be obtained by a classical technique, the linear convolution of criteria. Translated fromMatematicheskie Zametki, Vol. 58, No. 3, pp. 365–370, September, 1995. This work was financed by the Foundation for Basic Research of the Belarus Republic (grant No. 242 23-70).     

Influence of heat treatment on the structure and magnetic properties of the Co/Zr and Co/Hf multilayer amorphous films

The influence of annealing on the structure and magnetic properties of amorphous Co/Zr and Co/Hf multilayer films was studied with particular attention to the dependence of the magnetic properties, thermal stability and crystallization process on layer composition and thickness. The temperature at which crystallization commences increases from 400 to 460 °C as the layer thickness d_Zr or d_Hf increases from 6 to 18 Å, and decreases from 450 to 400 °C as d_Co increases from 12 to 18 Å. Multilayers containing 19–60 at% Zr were studied. The specific magnetization was found to increase even below the temperature at which crystallization commences. Our data are compared with non-multilayer Co–Zr amorphous films and rapidly quenched metallic glasses.     

Influence of diffusion and kinetic characteristics on the combustion of a carbon particle

The spherically symmetric steady-state problem of heterogeneous combustion for a carbon particle is discussed. The exact solution of this problem is obtained. The dimensionless mass flux through the particle surface is graphically represented as a function of oxygen concentration in the external domain. The rate ratio for the diffusion process and the kinetic process is introduced as a dimensionless characteristic of the combustion process. The dimensionless mass fluxes through the particle surface are graphically represented as functions of external constitutive parameters. The resulting solution is approximated. The diffusion and kinetic modes of combustion are considered as limiting cases.     

Weak ferromagnetism and spin density distributions in thin films of Gd x Bi1 − x FeO3 solid solutions

Polycrystalline thin-film Gd _x Bi_{1 ? x} FeO₃ (x = 0, 0.05, 0.10, 0.15, or 0.20) samples are synthesized by means of thermal vacuum deposition. The concentrations, temperatures, and magnetic field dependences of specific magnetization are studied. Self-consistent calculations of the spin density distribution are performed for R3c BiFeO₃ and Pnma Gd_0.25Bi_0.75FeO₃ using the density functional theory in the LSDA approximation.     

Features of magnetic properties of La x MnO3 + δ (0.815 ≤ x ≤ 1.0)

Magnetic and resonance studies of the system of polycrystalline samples of self-doped manganites La _x MnO_{3 + δ} (x = 0.815, 0.90, 0.94, 0.97, and 1.0) have been performed in a temperature range of 77–300 K. According to ⁵⁵Mn NMR data, all samples contain a ferromagnetic phase at 77 K. As the defect density increases (x changes from 1.0 to 0.815), samples become more magnetically ordered. In this case, the ferromagnetic state of the system gradually changes from a mixed state in which both ferromagnetic insulating (basic) and ferromagnetic metal (for x = 0.97 and 1.0) phases coexist to only the ferromagnetic metal state (for x = 0.815 and 0.90). It has been shown that both ferromagnetic metal and ferromagnetic insulating phases are inhomogeneous, and either phase consists of two phases with different dynamics of nuclear spins and different Curie temperatures. The diagram of the magnetic phase state of the La _x MnO_{3 + δ} system (x = 0.815, 0.90, 0.94, 0.97, 1.0) has been constructed for a temperature range of 120–240 K and Mn⁴⁺ contents of 12–30%.     

On the Edge of the Known: Extremely Electron-Rich (Di)Carboranyl Phosphines

The syntheses of the first B9-connected carboranylphosphines (B9-Phos) featuring two carboranyl moieties as well as access to B9-Phos ligands with bulky electron-donating substituents, previously deemed unattainable, is reported. The electrochemical properties of the B9-Phos ligands were investigated, revealing the ability of the mesityl derivatives to form stabilized phosphoniumyl radical cations. The B9-Phos ligands display an extremely electron-releasing character surpassing that of alkyl phosphines and commonly used N-heterocyclic carbenes. This is demonstrated by their very small Tolman electronic parameters (TEPs) as well as extremely low P−Se coupling constants. Cone angles and buried volumes attest to the high steric demand exerted by the (di)carboranyl phosphines. The dicarboranyl phosphine Au^I complexes show superior catalytic performance in the hydroamination of alkynes compared to the monocarboranyl phosphine analogs.     

Dielectric and optical properties of gadolinium doped bismuth ferrite

Polycrystalline samples of a Gd _x Bi_1?x FeO₃ system are prepared by a conventional ceramic technology. Temperature and frequency dependences of a component of permittivity in the range of radio- and ultra-high frequencies are investigated. Features of the behavior of the reflectance spectra and spectra of the components of the dielectric and optical functions in the region of lattice and electronic resonances are investigated.