The spin-transition properties of Fe(III) complexes with hetarylformazan in an ion-exchange polymer: An EPR study

For the first time, the EPR method was used to reveal and study the special features of spin-transition processes between high-spin and low-spin iron(III) complexes with hetarylformazans immobilized on an ion-exchange polymer. An analysis of completely reversible temperature dependences of EPR line positions, widths, and integral intensities in the spectra of high-spin and low-spin complexes allowed four temperature intervals to be identified. These intervals corresponded to preparative periods of spin-transition processes (450–275 K, intervals I and II), their appearance (275–230 K, interval III), and occurrence (230–100 K, interval IV). Local concentrations and spin exchange frequencies in clusters were estimated. Effects related to high-spin complex EPR signal shifts during temperature changes and to the duration of sample storage were revealed. High-spin complexes were found to be very sensitive to external actions, as distinct from very stable low-spin complexes. Experimental EPR observations obtained for ion-exchange polymer satisfied the concept of the nucleation and growth of domains in the spin-transition process.     

Electronic structure of p-type La1 ? xM x2+ MnO3 manganites in the ferromagnetic and paramagnetic phases in the LDA + GTB approach

The band structure, spectral intensity, and position of the Fermi level in doped p-type La_{1 − x} M _x/2+MnO₃ manganites (M = Sr, Ca, Ba) is analyzed using the LDA + GBT method for calculating the electronic structure of systems with strong electron correlations, taking into account antiferro-orbital ordering and using the Kugel-Khomskii ideas and real spin S = 2. The results of the ferromagnetic phase reproduce the state of a spin half-metal with 100% spin polarization at T = 0, when the spectrum is of the metal type for a quasiparticle with one spin projection and of the dielectric type for the other. It is found that the valence band becomes approximately three times narrower upon a transition to the paramagnetic phase. For the paramagnetic phase, metal properties are observed because the Fermi level is located in the valence band for any nonzero x. The dielectrization effect at the Curie temperature is possible and must be accompanied by filling of d _x orbitals upon doping. The effect itself is associated with strong electron correlations, and a complex structure of the top of the valence band is due to the Jahn-Teller effect in cubic materials.     

Electronic structure,magnetic properties,and mechanism of the insulator–metal transition in LaCoO<Subscript>3</Subscript> taking into account strong electron correlations

The electronic structure of LaCoO₃ at finite temperatures is calculated using the LDA+GTB method taking into account strong electron correlations and possible spin crossover upon an increase in temperature. Gap states revealed in the energy spectrum of LaCoO₃ reduce the dielectric gap width upon heating; this allowed us to describe the insulator-metal transition observed in this compound at T = 500–600 K. The temperature dependence of the magnetic susceptibility with a peak at T ≈ 100 K is explained by the Curie contribution from thermally excited energy levels of the Co³⁺ ion. At high temperatures, the Pauli contribution from a band electron is added and the total magnetization of LaCoO₃ is considered as the sum M _tot = M _loc + M _band. The second term describes the band contribution appearing as a result of the insulator-metal transition and facilitating the emergence of a high-temperature anomaly in the magnetic susceptibility of LaCoO₃.     

Tuning magnetotransport through a magnetic kink crystal in a chiral helimagnet

We consider magnetotransport properties in a conducting chiral helimagnet, where the magnetic kink crystal (MKC) is formed under weak magnetic field applied perpendicular to the helical axis. The MKC behaves as a magnetic superlattice potential and results in Bragg scattering of conduction electrons. Tuning of the weak magnetic field enables us to control the size of the superlattice Brillouin zone and gives rise to a series of divergent resistivity anomalies originating from resonant Bragg scatterings. We discuss as well a nontrivial magnetic structure in the resonant states realized in the subsystem of the itinerant electrons.     

Anomalous thermodynamics of the doped Mott-Hubbard insulators

The concentration dependence of the entropy of doped Mott-Hubbard insulators has been considered within the t-J model. It has been shown that a change in the type and statistics of charge carriers as compared to the Fermi gas leads to a radical change in the entropy s, in particular, to the giant growth of the entropy upon doping. The quantity ∂s/∂x ≈ k _B is approximately consistent with the experimental data for HTSC cuprates in the pseudogap phase.     

A supramolecular medical hydrogel based on <Emphasis Type="Italic">L</Emphasis>-cysteine and silver ions

A novel supramolecular thixotropic gel based on low-concentration aqueous solutions of L-cysteine and silver nitrate is synthesized. Self-organization and gel formation in the system of interest is studied by means of UV and IR spectroscopy, transmission electron microscopy, dynamic light scattering, and rotational viscometry. A model of the supramolecular gel is suggested. Possible applications for medicinal purposes are considered.     

Atomic layer deposition of thin films of titanium dioxide from titanium tetramethoxide and water

The atomic layer deposition of titanium oxide in the precursor systems Ti(OCH₃)₄-H₂O and Ti(OC₂H₅)₄-H₂O was compared. The growth rate of titanium oxide formed by the atomic layer deposition in the Ti(OCH₃)₄-H₂O system can be adequately estimated with due to regard for the number and size of ligands of a metal-containing precursor. The study in simulated body fluid solutions showed that polycrystallin TiO₂ coatings with anatase structure are prone to accelerated osseointegration and, consequently, promising for the development of new biomedical products.     

Quick ellipsometric technique for determining the thicknesses and optical constant profiles of Fe/SiO2/Si(100) nanostructures during growth

An algorithm is developed to perform rapid control of the thickness and optical constants of a film structure during growth. This algorithm is tested on Fe/SiO₂/Si(100) structures grown in an Angara molecular-beam epitaxy setup. The film thicknesses determined during their growth are compared with X-ray spectral fluorescence analysis and transmission electron microscopy data.     

Structures of Two Cyclotetrasiloxanes with Intra and Intercyclic –CH2CH2-Bridges

Molecular structures of two cyclotetrasiloxanes with intra and intercyclic ethylene bridges were determined by an X-ray structure analysis. The presence of the intracyclic bridge results in a saddle conformation, unusual for tetrasiloxane cycles, and in a significant strain of the cycle. The tetrasiloxane cycles linked by this bridge have a highly symmetric chair conformation which is likely to persist in the corresponding polymer.