Theoretical investigation of TbNi_{5-x}Cu_x optical properties

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations electronic structure for x=0,1,2 and on top of that optical conductivities were calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U densities of states (DOS) were taken into account via averaging over all possible Cu ion positions for given doping level x. Gradual suppression and loosing of structure of optical conductivity at 2 eV together with simultaneous intensity growth at 4 eV correspond to increase of Cu and decrease of Ni content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360 (2008)] plasma frequency has non monotonic doping behaviour with maximum at x=1. This behaviour is explained as competition between lowering of total density of states on the Fermi level N(E_F) and growing of number of carriers. Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure

Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)

In this paper we report comprehensive experimental and theoretical investigation of magnetic and electronic properties of the intermetallic compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these two systems was probed by optical measurements in the spectral range of 0.22-15 micrometers. On top of that charge carriers parameters (plasma frequency and relaxation frequency) and optical conductivity s(w) were determined. Self-consistent spin-resolved bandstructure calculations within the conventional LSDA+U method were performed. Theoretical interpetation of the experimental s(w) dispersions indicates transitions between 3d and 4p states of Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical optical conductivity coincides well with our experimental data. Calculated by LSDA+U method magnetic moments per formula unit are found to be in good agreement with observed experimental values of saturation magnetization.Comment: 16 pages, 5 figures, 1 tabl

Specific features of the electronic structure and spectral properties of NdNi5 - xCux compounds

The spectral properties of the intermetallic compounds NdNi5 - xCux (x = 0, 1, 2) have been studied using optical ellipsometry in the wavelength range 0.22-16 μm. It has been established that substitution of copper atoms for nickel leads to noticeable changes in the optical absorption spectra, plasma frequencies, and relaxation frequencies of conduction electrons. Spin-polarized calculations of the electronic structure of these compounds have been performed in the local spin density approximation allowing for strong electron correlations (LSDA + U method) in the 4f shell of the rare-earth ion. The calculated electron densities of states have been used to interpret the experimental dispersion curves of optical conductivity in the interband light absorption region. © 2013 Pleiades Publishing, Ltd

Optical spectroscopy and electronic structure of compounds HoNi 5-x Alx (x = 0, 1, 2)

The optical properties of the compounds HoNi5 - x Al x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined. © 2013 Pleiades Publishing, Ltd

Influence of aluminum impurity on the electronic structure and optical properties of the TbNi5 intermetallic compound

The electronic structure of the TbNi5 - xAlx intermetallic compounds (x = 0, 1, 2) is calculated in the local electron density approximation with the correction to strong electron correlations in 4f shell of terbium ions. Spectral properties of these compounds are measured by ellipsometry in a wavelength range of 0. 22-16 μm. Frequency dependences of optical conductivity in the region of interband optical absorption are interpreted based on the results of calculations of electron densities of states. The relaxation and plasma frequencies of conduction electrons are determined. © 2013 Pleiades Publishing, Ltd

Ab initio exchange interactions and magnetic properties of Gd2Fe17 iron sublattice: rhombohedral vs. hexagonal phases

In the framework of the LSDA+U method electronic structure and magnetic properties of the intermetallic compound Gd2Fe17 for both rhombohedral and hexagonal phases have been calculated. On top of that, ab initio exchange interaction parameters within the Fe sublattice for all present nearest and some next nearest Fe ions have been obtained. It was found that for the first coordination sphere direct exchange interaction is ferromagnetic. For the second coordination sphere indirect exchange interaction is observed to be weaker and of antiferromagnetic type. Employing the theoretical values of exchange parameters Curie temperatures Tc of both hexagonal and rhombohedral phases of Gd2Fe17 within Weiss mean-field theory were estimated. Obtained values of Tc and its increase going from the hexagonal to rhombohedral crystal structure of Gd2Fe17 agree well with experiment. Also for both structures LSDA+U computed values of total magnetic moment coincide with experimental ones.Comment: 20 pages, 2 figures; V2 as published in PR

ENDOTHELIAL PROTECTIVE ACTIVITY OF 2,6-DIISOBORNYL-4-METHYLPHENOL IN A MODEL OF MYOCARDIAL ISCHEMIA/REPERFUSION IN RATS

Objective: Our research focuses on the endothelial protective effects of 2,6-diisobornyl-4-methylphenol. Its effect was revealed while studying rats experiencing myocardial ischemia/reperfusion. The research results demonstrated that there are significant disturbances in the vascular endothelium manifested by a decrease in the vasodilating activity and antiplatelet properties of 2,6-diisobornyl-4-methylphenol. Methods: We designed our own model of myocardial ischemia/reperfusion and applied it to 52 adult outbred Wistar males. We employed some methods of hemostasiological research such as thromboelastography to determine the antiplatelet activity of the vascular wall, G. Born nephelometric method to study platelet aggregation, phase contrast microscopy to count platelet counts in blood plasma, measurement of intra-arterial pressure to study the endothelial vasodilating function, and calculated the endothelial dysfunction coefficient in rats. Results: Preventive intragastric injection of 2,6-diisobornyl-4-methylphenol (100 mg/kg, 3 days before and 5 days after reproducing the myocardial ischemia/reperfusion model) increased the antiplatelet activity of the vascular endothelium in rats by 37% compared to the endothelium of the abdominal aorta segment of untreated animals. Moreover, 2,6-diisobornyl-4-methylphenol decreased the endothelial dysfunction coefficient by 43% in comparison with the value in the control group. Conclusion: 2,6-diisobornyl-4-methylphenol has an endothelial protective effect proved by its ability to increase antiplatelet properties of the endothelium and decrease the endothelial dysfunction coefficient. The revealed endothelial protective properties of 2,6-diisobornyl-4-methylphenol can be regarded as one of the potential mechanisms of cardioprotective activity of the drug

Development of Cross-Section Library for DYN3D Code

At present, SSTC NRS uses the HELIOS code for generation of few-group cross-section libraries for WWER core calculations. There is an urgent issue of selecting the appropriate approach to implement the cross-section library into the DYN3D code. The paper overviews the application of approaches used by SSTC NRS, such as a multidimensional table and polynomial dependences. The capabilities and possible extension of each approach are described with inherent advantages and disadvantages. In addition, the model development and cross-section preparation for the WWER-1000 radial reflector taking into account discontinuity factors are discussed. Brief results of calculations with the use of different approaches are presented.На даний час ДНТЦ ЯРБ використовує спектральний код HELIOS для підготовки малогрупових бібліотек нейтронно-фізичних констант тепловидільних збірок (ТВЗ) активних зон ВВЕР. У процесі розробки моделей ТВЗ виникає актуальна проблема вибору правильного підходу до реалізації бібліотеки констант у коді DYN3D. У даній роботі надано результати досліджень підходів, що використовує ДНТЦ ЯРБ, — реалізації бібліотеки у вигляді багатовимірної таблиці й поліноміальних залежностей. Розглянуто підходи ДНТЦ ЯРБ до вирішення проблеми розробки моделі та підготовки нейтронно-фізичних констант радіального відбивача для ВВЕР-1000 з урахуванням факторів розривності. Наведено короткі результати розрахункових досліджень при використанні різних підходів.В настоящее время ГНТЦ ЯРБ использует спектральный код HELIOS для подготовки малогрупповых библиотек нейтронно-физических констант тепловыделяющих сборок активных зон ВВЭР. В ходе разработки моделей тепловыделяющих сборок возникает актуальная проблема выбора правильного подхода к реализации библиотеки констант в коде DYN3D. В данной роботе представлены результаты исследований подходов, используемых ГНТЦ ЯРБ, — реализации библиотеки в виде многомерной таблицы и полиномиальных зависимостей. Показаны подходы к решению проблемы разработки модели и подготовки нейтронно-физических констант радиального отражателя для ВВЭР- 1000 с учетом факторов разрывности. Даны краткие результаты расчетных исследований при использовании различных подходов

Copper-doping effects in electronic structure and spectral properties of SmNi5

The electronic structure and optical properties of the SmNi5-xCux (x = 0, 1, 2) compounds are studied. The band spectra of the studied intermetallics were calculated with LDA + U + SO method supplementing the local density approximation with a correction for strong electron interaction on the shell of the rare-earth element. Optical properties were studied by ellipsometry method in the wide wavelength range. It was found that the substitution of copper for nickel leads to local changes in the optical conductivity spectra. Both the spectroscopic measurements and theoretical calculations demonstrate the presence of a broad absorption band around 4 eV associated with the Cu 3d → Ni 3d electron transitions and increasing with the grown of copper content. The experimental dispersion curves of optical conductivity in the interband absorption region were interpreted using the results of the calculations. © 2015 AIP Publishing LLC

Electronic Structure, Magnetic, and Optical Properties of the Intermetallic Compounds R2 Fe17 (R=Pr,Gd)

In this paper we report comprehensive experimental and theoretical investigation of magnetic and electronic properties of the intermetallic compounds Pr2 Fe17 and Gd2 Fe17. Electronic structure of these two systems was probed by optical measurements in the spectral range of 0.22-15 μm. On top of that, charge-carrier parameters (plasma frequency Ω and relaxation frequency γ) and optical conductivity σ(ω) were determined. Self-consistent spin-resolved band-structure calculations within the conventional LSDA+U method were performed. Theoretical interpretation of the experimental σ(ω) dispersions indicates transitions between 3d and 4p states of Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical optical conductivity coincides well with our experimental data. Calculated by the LSDA+U method magnetic moments per formula unit are found to be in good agreement with observed experimental values of saturation magnetization. © 2006 The American Physical Society.This work was supported by Grants from the Russian Foundation for Basic Research, Grant Nos. 05-02-17244, 04-02-16096, and 05-02-16301 and in part by programs of the Presidium of the Russian Academy of Sciences (RAS) “Quantum macrophysics” and of the Division of Physical Sciences of the RAS “Strongly correlated electrons in semiconductors, metals, superconductors and magnetic materials.” Two of us I.N., A.L. acknowledge Dynasty Foundation and International Center for Fundamental Physics in Moscow and Russian Science Support Foundation, Grant of President of Russia MK-02.2118.2005 and interdisciplinary UrO-SO project (I.N.)