Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics

A simple but general microscopic mechanism to understand the interplay between the electric and magnetic degrees of freedom is developed. Within this mechanism, the magnetic structure generates an electric current which induce an counterbalance electric current from the spin orbital coupling. When the magnetic structure is described by a single order parameter, the electric polarization is determined by the single spin orbital coupling parameter, and the material is predicted to be a half insulator. This mechanism provides a simple estimation of the value of ferroelectricity and sets a physical limitation as well.Comment: 4 pages, 1 figur

Non-circular semiconductor nanorings of type I and II: Emission kinetics in the exciton Aharonov-Bohm effect

Transition energies and oscillator strengths of excitons in dependence on magnetic field are investigated in type I and II semiconductor nanorings. A slight deviation from circular (concentric) shape of the type II nanoring gives a better observability of the Aharonov-Bohm oscillations since the ground state is always optically active. Kinetic equations for the exciton occupation are solved with acoustic phonon scattering as the major relaxation process, and absorption and luminescence spectra are calculated showing deviations from equilibrium. The presence of a non-radiative exciton decay leads to a quenching of the integrated photoluminescence with magnetic field.Comment: The first version submitted to Phys. Rev. B on April 16, 2007. Revised (this) version on July 31, 200

Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction

The intriguing nano-structural properties of a ZnMnGaO4 film epitaxially grown on MgO (001) substrate have been investigated using synchrotron radiation-based x-ray diffraction. The ZnMnGaO4 film consisted of a self-assembled checkerboard (CB) structure with perfectly aligned and regularly spaced vertical nanorods. The lattice parameters of the orthorhombic and rotated tetragonal phases of the CB structure were analyzed using H-K, H-L, and K-L cross sections of the reciprocal space maps measured around various symmetric and asymmetric reflections of the spinel structure. We demonstrate that the symmetry of atomic displacements at the phases boundaries provides the means for coherent coexistence of two domains types within the volume of the film

\u3ci\u3eIn-Situ\u3c/i\u3e Raman Scattering Studies of Alkali-Doped Single Wall Carbon Nanotubes

Electrochemical doping and in-situ Raman scattering were used to study charge transfer in K- and Li-doped single wall carbon nanotubes (SWNT) as a function of alkali concentration. An 8 cm-1 downshift was observed for the tangential phonon mode of SWNT doped to stoichiometries of KC24 and Li1.25C6. The shift in both systems is reversible upon de-doping despite an irreversible loss of crystallinity. These results indicate that the tangential mode shifts result from electron transfer from alkali dopants to the SWNT, and that these modes are only weakly affected by long-range order within the ropes

Coupling between magnon and ligand-field excitations in magnetoelectric Tb3Fe5O12 garnet

The spectra of far-infrared transmission in Tb3Fe5O12 magnetoelectric single crystals have been studied in the range between 15 and 100 cm-1, in magnetic fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some of the observed infrared-active excitations to electric-dipole transitions between ligand-field split states of Tb3+ ions. Anticrossing between the magnetic exchange excitation and the ligand-field transition occurs at the temperature between 60 and 80 K. The corresponding coupling energy for this interaction is 6 cm-1. Temperature-induced softening of the hybrid IR excitation correlates with the increase of the static dielectric constant. We discuss the possibility for hybrid excitations of magnons and ligand-field states and their possible connection to the magnetoelectric effect in Tb3Fe5O12.Comment: submitted to Phys. Rev. B on May 15th, 201

Stabilizing effect of nuclear quadrupole interaction on the polarization of electron-nuclear spin system in a quantum dot

Nuclear quadrupole interaction extends the limits imposed by hyperfine interaction on the spin coherence of the electron and nuclei in a quantum dot. The strain-induced nuclear quadrupole interaction suppresses the nuclear spin flip and makes possible the zero-field dynamic nuclear polarization in self-organized InP/InGaP quantum dots. The direction of the effective nuclear magnetic field is fixed in space, thus quenching the magnetic depolarization of the electron spin in the quantum dot. The quadrupole interaction suppresses the zero-field electron spin decoherence also for the case of non-polarized nuclei. These results provide a new vision of the role of the nuclear quadrupole interaction in nanostructures: it elongates the spin memory of the electron-nuclear system.Comment: 18 pages including 3 figures. Shortened version has been accepted for publication in Physical Review Letter

Вивчення параметрів гострої та підгострої токсичності препарату “Рибохін” на моделі коропа

The goal of the work was to study of acute and subacute toxicity parameters of “Rybokhin” biological product (AI – chloroquine refer to derivatives 4-aminohinolines) on the model of carp. This drug is effective in the treatment of diseases caused by parasitic Protozoa and Monogenea. Carp scales of two years old were used in experiments. To determine acute toxicity, the fish were prescribed with chloroquine (by AI) in doses of 100; 200; 300; 400; 500; 600; 800; 1000 mg/kg of live weight. Two experimental and control fish groups of 30 individuals each were formed to determine subacute toxicity of “Rybokhin”. Experimental groups of fish were prescribed with “Rybokhin” in a dose (by AI) of 50 mg/kg and 10 mg/kg for two consecutive days. Blood samples were collected from six fish species from each group for clinical and biochemical indicators after 48 hours, 7, 14, 21 and 28 days. The hemoglobin content, number of red blood cells and leukocytes blood were determined. The intensity of peroxide oxidation of lipids (PОL), catalase activity, level of total antioxidant capacity (TAC), total proteins, albumin, globulins and glucose, circulating immune complexes (CІC) and seromucoids concentration, level of enzymatic activity: aspartate transaminase (АSТ), alanine transaminase (АLТ), ά-amylase blood plasma were determined. According to the research results, indicators of acute toxicity for carp were determined, namely LD50 of chloroquine is 528.66 ± 68.01 mg/kg; LD16 – 224.512 mg/kg; LD84 – 832.81 mg/kg; LD100 – 984.89 mg/kg, which indicate that the drug is low-toxic to fish (belongs to the fourth group of toxicity). When administrating of 50.0 mg/kg of “Rybokhin” (by AI) twice a day, the most expressed metabolic changes in fish body were observed on 21 day after its last administration. Thus, the drug’s toxic impact is in proteinogram alteration, transamination processes and in decreasing of fish immune reactivity. It points to the prevalence of catalytic processes over anabolic. Metabolic alterations are obviously directed to the activation of detoxication processes with increased energy use in fish body after getting of higher dosage of the product. So, on 28 day of experiment, the major part of studied parameters retrieved to control level. It was found that when the product was administrated twice a day in the dosage 10.0 mg/kg (by AI), which is used for treatment of parasitic diseases, no reliable changes of clinical and biochemical indices were detected in fish blood during the experiment.Метою досліджень було визначити параметри гострої та підгострої токсичності препарату “Рибохін” (ДР – хлорохін, якій є похідною 4-амінохінолінів) на моделі коропа лускатого. Даний препарат є ефективним при лікуванні захворювань, спричинених паразитичними найпростішими (Protozoa) та моногенетичними присиcнями (Monogenea). У експериментах використовували коропа лускатого дволітнього віку. При визначенні гострої токсичності рибам задавали хлорохін (ДР) у дозах 100; 200; 300; 400; 500; 600; 800; 1000 мг/кг маси тіла. Для визначення підгострої токсичності препарату “Рибохін” було сформовано дві дослідні та контрольна групи риб по 30 особин у кожній. Рибі дослідних груп дві доби поспіль задавали препарат “Рибохін” у добовій дозі 50 мг/кг та 10 мг/кг маси тіла (за ДР). Через 48 год, 7, 14, 21 та 28 діб з метою клініко-біохімічних досліджень проводили відбір крові у шести особин риб з кожної групи. У крові визначали вміст гемоглобіну, кількість еритроцитів і лейкоцитів. У плазмі крові визначали інтенсивність процесів пероксидного окиснення ліпідів (ПОЛ), каталазну активність, рівень загальної антиокиснювальної активності (загальна АОА); вміст загальних протеїнів, альбуміну і глюкози; концентрацію циркулюючих імунних комплексів (ЦІК) і серомукоїдів; рівень ензиматичної активності: аспартатамінотрансферази (АсАТ), аланінамінотрансферази (АлАТ) і ά-амілази. За результатами досліджень визначено показники гострої токсичності для коропа: LD50 хлорохіну становить 528,66 ± 68,01 мг/кг; LD16 – 224,512 мг/кг; LD84 – 832,81 мг/кг; LD100 – 984,89 мг/кг маси тіла, які вказують, що препарат є малотоксичним для риб (належить до четвертої групи токсичності). Максимальну вираженість метаболічних змін в організмі риб за дворазового застосування препарату “Рибохін” в добовій дозі 50,0 мг/кг маси тіла (за ДР) виявляли на 21-шу добу після останнього задавання. Так, механізми токсичної дії препарату полягають у перебудовах в протеїнограмі і процесах переамінування та гальмуванні імунної реактивності в організмі риб, що вказує на превалювання катаболічних процесів над анаболічними. Метаболічні перебудови, очевидно, спрямовані на активацію процесів детоксикації з підвищенням енергетичних затрат в організмі риби внаслідок потрапляння підвищених доз препарату. Отже, на 28-му добу експерименту левова частка досліджених показників за значенням відновлювалась до контрольного рівня. Встановлено, що за дворазового введення препарату в добовій дозі 10,0 мг/кг маси тіла (за ДР), яка є лікувальною при боротьбі із паразитарними хворобами, у динаміці експерименту не виявляли достовірних змін клініко-біохімічних показників крові дослідних риб

Acceptor binding energies in GaN and AlN

We employ effective mass theory for degenerate hole-bands to calculate the acceptor binding energies for Be, Mg, Zn, Ca, C and Si substitutional acceptors in GaN and AlN. The calculations are performed through the 6$\times$6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonians for wurtzite (WZ) and zincblende (ZB) crystal phases, respectively. An analytic representation for the acceptor pseudopotential is used to introduce the specific nature of the impurity atoms. The energy shift due to polaron effects is also considered in this approach. The ionization energy estimates are in very good agreement with those reported experimentally in WZ-GaN. The binding energies for ZB-GaN acceptors are all predicted to be shallower than the corresponding impurities in the WZ phase. The binding energy dependence upon the crystal field splitting in WZ-GaN is analyzed. Ionization levels in AlN are found to have similar `shallow' values to those in GaN, but with some important differences, which depend on the band structure parameterizations, especially the value of crystal field splitting used.Comment: REVTEX file - 1 figur

Optical identification of hybrid magnetic and electric excitations in Dy3Fe5O12 garnet

Far-infrared spectra of magneto-dielectric Dy3Fe5O12 garnet were studied between 13 and 100 cm-1 and at low temperatures between 5 and 80 K. A combination of transmission, reflectivity, and rotating analyzer ellipsometry was used to unambiguously identify the type of the dipole activity of the infrared modes. In addition to purely dielectric and magnetic modes, we observed several hybrid modes with a mixed magnetic and electric dipole activity. These modes originate from the superexchange between magnetic moments of Fe and Dy ions. Using 4x4 matrix formalism for materials with Mu=/=1, we modeled the experimental optical spectra and determined the far-infrared dielectric and magnetic permeability functions. The matching condition Mu(Wh)*Se=Eps(Wh)*Sm for the oscillator strengths Se(m) explains the observed vanishing of certain hybrid modes at Wh in reflectivity.Comment: paper and supplement appendi

Effect of the Surface on the Electron Quantum Size Levels and Electron g-Factor in Spherical Semiconductor Nanocrystals

The structure of the electron quantum size levels in spherical nanocrystals is studied in the framework of an eight--band effective mass model at zero and weak magnetic fields. The effect of the nanocrystal surface is modeled through the boundary condition imposed on the envelope wave function at the surface. We show that the spin--orbit splitting of the valence band leads to the surface--induced spin--orbit splitting of the excited conduction band states and to the additional surface--induced magnetic moment for electrons in bare nanocrystals. This additional magnetic moment manifests itself in a nonzero surface contribution to the linear Zeeman splitting of all quantum size energy levels including the ground 1S electron state. The fitting of the size dependence of the ground state electron g factor in CdSe nanocrystals has allowed us to determine the appropriate surface parameter of the boundary conditions. The structure of the excited electron states is considered in the limits of weak and strong magnetic fields.Comment: 11 pages, 4 figures, submitted to Phys. Rev.