Synthesis and Thermal Conversions of Unsaturated Cobalt(II) Monocarboxylates: Precursors for Metal Polymer Nanocomposites

Cobalt(II) salts of unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, sorbic acid, 4-pentynoic acid, crotonic acid, linoleic acid, and oleic acid) are prepared. The prepared compounds are characterized by elemental analysis, IR spectroscopy, thermogravimetry, and differential scanning calorimetry. Cobalt-containing nanocomposites are produced by the thermal decomposition of the prepared carboxylates and characterized by elemental analysis, IR spectroscopy, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray powder diffraction. The enthalpies of reaction (ΔH_r°) for the formation of cobalt(II) salts of unsaturated monocarboxylic acids are calculated by the PM3 semiempirical quantum-chemical method. A correlation is found between the mean diameter (d_mean) of nanoparticles in nanocomposites and ΔH_r°.     

Silicide formation in bilayer ultrathin iron and cobalt films on silicon

The processes that occur in ultrathin (up to 1 nm) Fe and Co layers during deposition onto the Si(100)2 × 1 surface in various sequences and during annealing of the formed structures to a temperature of 400°C are studied. The elemental and chemical compositions of the films are analyzed by in situ high-resolution X-ray photoelectron spectroscopy using synchrotron radiation, and their magnetic properties are determined using the magnetic linear dichroism effect in the angular distribution of Fe 3p and Co 3p electrons. It is shown that, when iron is first deposited, the formed structure consists of the layers of FeSi, Fe₃Si, Co-Si solid solution, and metallic cobalt with segregated silicon. The structure formed in the alternative case consists of the layers of CoSi, Co-Si solid solution, Co, Fe-Si solid solution, and Fe partly covered by silicon. All layers (apart from FeSi, CoSi) form general magnetic systems characterized by ferromagnetic ordering. Annealing of the structures at temperatures above 130dgC (for the Co/Fe/Si system) and ～200°C (for Fe/Co/Si) leads to the formation of nonmagnetic binary and ternary silicides (Fe _x Co_{1 ? x} Si, Fe _x Co_{2 ? x} Si).     

Internal field and self-polarization in lead zirconate titanate thin films

It has been shown that 300-nm-thick polycrystalline films of lead zirconate titanate (PZT), the compositions of which correspond to the region of morphotropic phase boundary, undergo anomalous changes in the composition and the microstructure as the annealing temperature increases. This causes substantial variations in the dielectric and piezoelectric responses, the spontaneous polarization and the internal field value. It has been demonstrated that the self-polarization varies nonmonotonically with increasing the internal field and is characterized by a threshold effect. The role of excess lead oxide and its influence on the formation of the self-polarization and the change in the effective permittivity of the ferroelectric layer has been discussed.     

Formation of ultrathin magnetic cobalt films on the Si(111)7 × 7 surface

The phase composition, electronic structure, and magnetic properties of ultrathin cobalt films (no thicker than 20 ?) applied on a Si(111)7 × 7 surface at room temperature are studied by high-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism. It is shown that, as the cobalt thickness increases, first interface cobalt silicide and then an island (discontinuous) film of silicon-in-cobalt solid solution form on the silicon surface. A metal cobalt film starts growing after the deposition of a ∼7-?-thick Co layer. It is found that the ferromagnetic ordering of the system, which is characterized by surface magnetization, sets in after the deposition of a ∼6-?-Co layer at the stage of Co-Si solid solution formation.     

Electro-and magnetotransport properties of disordered carbon phases synthesized from C60 fullerite at moderate pressures P syn < 1.5 GPa

Charge transport has been investigated in new disordered carbon phases synthesized from C₆₀ at “moderate” pressures P _syn < 1.5 GPa and high temperatures T _syn > 1000 K. Under these synthesis conditions, a structure transition from nanographite phases to new amorphous modifications is induced when pressure decreases. The transition from hopping transport to diffusive electron transport typical of “dirty” metals is observed in a number of samples synthesized at various pressures and temperatures in the indicated ranges. The magnetotransport properties of these phases under intermediate synthesis conditions can be described by diffusive electron transport.     

Features of the formation of a perovskite phase in thin polycrystalline Pb(Zr,Ti)O<Subscript>3</Subscript> films

The structure and dielectric properties of thin lead zirconate titanate Pb(Zr,Ti)O₃ films grown ex situ on a silicon substrate are studied using various methods (X-ray analysis, raster electron microscopy, atomic-force microscopy, optical microscopy, and dielectric measurements). It is shown that, upon increase in the crystallization temperature, the growth texture of the films changes, leading to a change of their dielectric parameters.     

Observation of Magnetic-Field-Induced Electric Polarization in Terbium Orthoferrite

JETP Letters - In TbFeO3 orthoferrite at temperatures below the antiferromagnetic ordering temperature for the terbium subsystem (～3.2 K), the electric polarization Pa(Hb) induced by a...