Microscopic mechanisms of spin-dependent electric polarization in 3d oxides

We present a short critical overview of different microscopic models for nonrelativistic and relativistic magnetoelectric coupling including the so-called "spin current scenario", ab-initio calculations, and several recent microscopic approaches to a spin-dependent electric polarization in 3d oxides.Comment: 8 pages, 3 figure

ФЛУОРИМЕТРИЧЕСКОЕ ОПРЕДЕЛЕНИЕ ФЕНОЛА В ВОЗДУХЕ РАБОЧЕЙ ЗОНЫ С ХРОМАТОМЕМБРАННОЙ ЖИДКОСТНОЙ АБСОРБЦИЕЙ

This work is devoted to development scheme of continuous on-line control of the content of phenol in working area air using chromatomembrane liquid absorption and fluorimetric detection. Optimal rates of gas and liquid phases were determined and good convergence between continuous chromatomembrane liquid absorption variant of analysis and classic absorption into bubbler with chromatographic detection were shown. Completeness of absorption of phenol in a continuous chromatomembrane liquid absorption were determined not less than 98 %. Benefits of the developed scheme are simple automation, minimal time of operator parcipitation during analysis, no reagents using. It is possible to determine concentration of phenol in working area air in the range of 20 % of the maximum permissible concentration of up to 5 MPC with a frequency of 3-4 tests per hour.Keywords: chromatomembrane liquid absorption, automation of analysis, monitoring of the environment(Russian)DOI: http://dx.doi.org/10.15826/analitika.2013.17.4.016A. L. Moskvin, A. N. MelnichenkoFederal State Budgetary Educational Institution of Higher Professional Education «Saint Petersburg State University», Saint-Petersburg, Russian FederationРабота посвящена разработке схемы непрерывного on-line контроля содержания фенола в воздухе рабочей зоны с хроматомембранной жидкостной абсорбцией и флуориметрическим детектированием. Подобраны оптимальные для проведения измерений расходы жидкой и газовой фазы и показана хорошая сходимость результатов непрерывного варианта определения фенола в воздухе рабочей зоны с хроматомембранной жидкостной абсорбцией с классическим вариантом поглощения в барботёре с хроматографическим определением. Определена полнота поглощения фенола в условиях непрерывной абсорбции в хроматомембранной ячейке на уровне не менее 98 %. Преимуществами разработанной схемы являются: простота автоматизации, минимальное участие оператора, отсутствие необходимости использования реактивов. Возможно определение содержания фенола в воздухе рабочей зоны по предложенной схеме в диапазоне от 20 % от предельно допустимой концентрации до 5 ПДК с частотой 3-4 анализа в час.Ключевые слова: хроматомембранная жидкостная абсорбция, автоматизация анализа, контроль объектов окружающей средыDOI: http://dx.doi.org/10.15826/analitika.2013.17.4.01

Interplay of p-d and d-d charge transfer transitions in rare-earth perovskite manganites

We have performed both theoretical and experimental study of optical response of parent perovskite manganites RMnO_3 with a main goal to elucidate nature of clearly visible optical features. Starting with a simple cluster model approach we addressed the both one-center (p-d) and two-center (d-d) charge transfer (CT) transitions, their polarization properties, the role played by structural parameters, orbital mixing, and spin degree of freedom. Optical complex dielectric function of single crystalline samples of RMnO_3 (R=La, Pr, Nd, Sm, Eu) was measured by ellipsometric technique at room temperature in the spectral range from 1.0 to 5.0 eV for two light polarizations: E \parallel c and E \perp c. The comparative analysis of the spectral behavior of \varepsilon _1 and \varepsilon _2 is believed to provide a more reliable assignment of spectral features. We have found an overall agreement between experimental spectra and theoretical predictions based on the theory of one-center p-d CT transitions and inter-site d-d CT transitions. Our experimental data and theoretical analysis evidence a dual nature of the dielectric gap in nominally stoichiometric matrix of perovskite manganites RMnO_3, it is formed by a superposition of forbidden or weak dipole allowed p-d CT transitions and inter-site d-d CT transitions. In fact, the parent perovskite manganites RMnO_3 should rather be sorted neither into the CT insulator nor the Mott-Hubbard insulator in the Zaanen, Sawatzky, Allen scheme.Comment: 20 pages, 6 figure

Stepwise Injection Potentiometric Determination of Ammonium-Ions in Water

Abstract An automatized technique of stepwise injection potentiometric determination of ammonium-ions in water is developed. The technique includes consecutive stages of evolution of ammonium-ions in the form of ammonia and its liquid absorption into water phase. The determination range is of 5 to 2000 µg/l and efficiency of 7 determinations per hour

NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2

We report on {6,7}Li nuclear magnetic resonance measurements of the spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered states. Below T about 24 K the NMR lineshape presents a clear signature of incommensurate (IC) static modulation of the local magnetic field consistent with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong phason-like dynamical fluctuations extending well below 24 K. We hypothesize that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's staircase" type behavior generic for IC systems. LDA based calculations of exchange integrals reveal a large in-chain frustration leading to a magnetical spiral.Comment: 4 pages, 4 figure

Flow methods as a general approach to automation of the chemical analysis of aqueous media (review)

Предлагаемая статья посвящена рассмотрению общих подходов к автоматизации анализа водных сред, являющихся основными объектами химического анализа: природных и сбросных вод, а также технологических сред в различных областях промышленности: микроэлектронике, биохимических производствах, атомной и тепловой энергетике, являющихся главными потребителями воды высокой чистоты, необходимой для предпусковых промывок внутриконтурного оборудования до требуемых кондиций чистоты его поверхностей, для приготовления теплоносителей, обеспечивающих функционирование ядерно- и теплоэнергетических объектов. Во всех перечисленных случаях жестко регламентируется содержание примесей в используемых или отработанных и подлежащих сбросу водных средах. Поскольку изменение содержания примесей в контролируемых средах часто происходит спонтанно и связано с отказами в работе оборудования контролируемых объектов, для оперативного реагирования на них и для их своевременного устранения химико-технологический контроль нормируемых параметров водных сред любого из названных происхождения и назначения предпочтительно осуществлять в непрерывном автоматическом режиме on-line, гарантирующем исключение пропусков или задержек в получении информации об отказах оборудования в контролируемом объекте в случае технологического контроля или о несанкционированных сбросах загрязняющих веществ в случае экологического контроля. Исходя из этих предпосылок, рассматриваются возможные методические подходы к созданию систем непрерывного химического контроля качества или загрязненности водных сред, и обсуждается предпочтительность для этих целей различных вариантов проточных методов в порядке их появления в арсенале химиков-аналитиков.The article is devoted to the consideration of general approaches to automating the analysis of aqueous media, which are the main objects of chemical analysis including natural and waste waters, as well as technological media in various industries (microelectronics, biochemical industries, nuclear and thermal power engineering), which are the main consumers of high-purity water used for pre-start flushing of inline equipment to the required cleanliness of surfaces, for preparation of coolants that ensure the operation of nuclear and thermal power plants. In all these cases, the content of impurities in used or spent and intended for discharge aqueous media is strictly regulated. Changes in the content of impurities in controlled media often occur spontaneously due to equipment failure on the controlled objects. Prompt response to such changes and their timely elimination can be performed more efficiently if chemical and technological control of the normalized parameters of aqueous media of any named origin and destination is carried out in a continuous automatic, on-line, mode, which guarantees the exclusion of gaps or delays in obtaining information about equipment failure on a controlled facility in case of technological control or about unauthorized discharges of pollutants in case of environmental control. Possible methodological approaches to the development of systems for continuous chemical monitoring of quality or levels of contamination of aqueous media are considered on the basis of the above prerequisites, and applicability of various flow methods for these purposes is discussed in the order of their appearance in the arsenal of analytical chemists

Lattice Distortion and Magnetism of 3d-t2gt_{2g} Perovskite Oxides

Several puzzling aspects of interplay of the experimental lattice distortion and the the magnetic properties of four narrow $t_{2g}$-band perovskite oxides (YTiO$_3$, LaTiO$_3$, YVO$_3$, and LaVO$_3$) are clarified using results of first-principles electronic structure calculations. First, we derive parameters of the effective Hubbard-type Hamiltonian for the isolated $t_{2g}$ bands using newly developed downfolding method for the kinetic-energy part and a hybrid approach, based on the combination of the random-phase approximation and the constraint local-density approximation, for the screened Coulomb interaction part. Then, we solve the obtained Hamiltonian using a number of techniques, including the mean-field Hartree-Fock (HF) approximation, the second-order perturbation theory for the correlation energy, and a variational superexchange theory. Even though the crystal-field splitting is not particularly large to quench the orbital degrees of freedom, the crystal distortion imposes a severe constraint on the form of the possible orbital states, which favor the formation of the experimentally observed magnetic structures in YTiO$_3$, YVO_, and LaVO$_3$ even at the HF level. Beyond the HF approximation, the correlations effects systematically improve the agreement with the experimental data. Using the same type of approximations we could not reproduce the correct magnetic ground state of LaTiO$_3$. However, we expect that the situation may change by systematically improving the level of approximations for dealing with the correlation effects.Comment: 30 pages, 17 figures, 8 tables, high-quality figures are available via e-mai

Interplay of p-d and d-d Charge Transfer Transitions in Rare-Earth Perovskite Manganites

We have performed both theoretical and experimental studies of optical response of parent perovskite manganites R MnO3 with a main goal to elucidate nature of clearly visible optical features. Starting with a simple cluster model approach we addressed the both one-center (p-d) and two-center (d-d) charge transfer (CT) transitions, their polarization properties, the role played by structural parameters, orbital mixing, and spin degree of freedom. Optical complex dielectric function of single-crystalline samples of R MnO 3 (R=La, Pr, Nd, Sm, Eu) was measured by ellipsometric technique at room temperature in the spectral range from 1.0 to 5.0 eV for two light polarizations: E∥c and E⊥c. The comparative analysis of the spectral behavior of ε1 and ε2 is believed to provide a more reliable assignment of spectral features. We have found an overall agreement between experimental spectra and theoretical predictions based on the theory of one-center p-d CT transitions and intersite d-d CT transitions. Our experimental data and theoretical analysis evidence a dual nature of the dielectric gap in nominally stoichiometric matrix of perovskite manganites R MnO3, it is formed by a superposition of forbidden or weak dipole allowed p-d CT transitions and intersite d-d CT transitions. In fact, the parent perovskite manganites R MnO3 should rather be sorted neither into the CT insulator nor the Mott-Hubbard insulator in the Zaanen, Sawatzky, Allen scheme. © 2010 The American Physical Society.We thank R. V. Pisarev for fruitful discussions. The present work was partly supported by the RFBR under Grants No. 08-02-00633 and No. 10-02-96032 (A.S.M.), the DPS program “Physics of new materials and structures” (N.N.L)