106 research outputs found
Electron spin resonance in the =1/2 quasi-one-dimensional antiferromagnet with Dzyaloshinskii-Moriya interaction BaCuGeO
We have investigated the electron spin resonance (ESR) on single crystals of BaCuGeO at temperatures between 300 and 2 K and in a large frequency band, 9.6 -134 GHz, in order to test the predictions of a recent theory, proposed by Oshikawa and Affleck (OA), which describes the ESR in a =1/2 Heisenberg chain with the Dzyaloshinskii-Moriya interaction. We find, in particular, that the ESR linewidth, , displays a rich temperature behavior. As the temperature decreases from 170 K to 50 K, shows a rapid and linear decrease, . At low temperatures, below 50 K, acquires a strong dependence on the magnetic field orientation and for it shows a behavior which is due to an induced staggered field , according to OA's prediction
Magnetic anisotropy of BaCu2Si2O7: theory and antiferromagnetic resonance
Antiferromagnetic resonance (AFMR) of BaCu2Si2O7 and a microscopic theory of
the magnetic anisotropy of spin 1/2 chain compounds with folded CuO3 geometry
being in good agreement with the available data are presented. The AFMR studies
at 4.2 K show the existence of two gaps (40 and 76 GHz) at zero magnetic field
and of two spin re-orientation transitions for H||c. The microscopic origin of
the two gaps is shown to be Hund's rule coupling which leads to a "residual
anisotropy" beyond the compensation of the Dzyaloshinskii-Moriya term by the
symmetric anisotropy which would be valid without Hund's coupling.Comment: 4 pages, 3 figure
Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains
By means of thermal expansion and specific heat measurements on the
high-pressure phase of (VO)PO, the effects of two energy scales of
the weakly dimerized antiferromagnetic = 1/2 Heisenberg chain are explored.
The low energy scale, given by the spin gap , is found to manifest
itself in a pronounced thermal expansion anomaly. A quantitative analysis,
employing T-DMRG calculations, shows that this feature originates from changes
in the magnetic entropy with respect to , . This term, inaccessible by specific heat, is visible only in the
weak-dimerization limit where it reflects peculiarities of the excitation
spectrum and its sensitivity to variations in .Comment: 4 pages, 4 figures now identical with finally published versio
Optimization of Vaccine Virus Accumulation in the Development of Smallpox Drugs Based on Cell Cultures
Objective. Optimization of vaccine virus cultivation in the suspended cell culture BHK-21 for infectious activity increment of virus-containing suspension as the base material for smallpox vaccine preparations. Materials and methods. We used suspended culture line of the cells BHK-21 of 72-hour age and nutrient medium of the MEM type in accordance with the guidelines on preparation in our studies. For challenging of the cells, vaccine virus (strain B-51) was used. The virus was adapted through three consequent passages on horion-allantois shell of developing chicken embryos of commercial dermovaccine series 449а at the premises of the Federal State Budgetary Institution “the 48th Central Research Institute” of the Ministry of Defense of the Russian Federation. Information on its genetic features is absent. Cultivation and precipitation of infected cells BHK-21 was carried out in bioreactor with priming volume of 1 liter at (36.5±0.5) °C and aeration with air mixture with varying content of CO2. Results and conclusions. Gas massexchange intensity was enhanced alongside simultaneous maintaining of sparing hydrodynamic conditions for mixing suspended cell cultures in bioreactor. Two-fold increase (up to (4.48±0.63)·109 cell/l) in suspended BHK-21 cell culture concentration at the end of reproduction cycle was achieved. Concentration of the vaccine virus was 3–5 times raised, from (8.1±0.3) lg PFU (plaque forming unit)/ml up to the level of infectious activity – (8.8±0.3) lg PFU/ml. Specific multiplicity of cell infection in recalculation per a cell was 1–5 PFU/cell and by virus yield – 20–100 PFU/cell. Enhanced infectious activity of the virus in concentrated suspension of infected BHK-21 cells substantiates the perspectives of the proposed method for improvement of vaccine virus accumulation phase in the development of anti-smallpox preparations based on cell cultures
Exchange broadening of EPR line in ZnO:Co
We study the X-band EPR spectra of Co²⁺ in single crystalline Zn₁₋xCoxO (x = 0.001–0.075) thin films grown by plasma-assisted molecular beam epitaxy. By analyzing the EPR linewidth behavior we argue that the exchange-narrowing model, usually applied to Mn-based II-VI DMS, fails here and that a combined effect of exchange and dipolar broadening can explain the linewidth variation with Co content and temperature
Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds
The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.Comment: 38 pages, 15 figure
Low temperature properties of the Electron Spin Resonance in YbRh2Si2
We present the field and temperature behavior of the narrow Electron Spin
Resonance (ESR) response in YbRh2Si2 well below the single ion Kondo
temperature. The ESR g factor reflects a Kondo-like field and temperature
evolution of the Yb3+ magnetism. Measurements towards low temperatures (>0.5K)
have shown distinct crossover anomalies of the ESR parameters upon approaching
the regime of a well defined heavy Fermi liquid. Comparison with the field
dependence of specific heat and electrical resistivity reveal that the ESR
parameters can be related to quasiparticle mass and cross section and, hence,
contain inherent heavy electron properties.Comment: 4 pages, 6 figures; Manuscript for Proceedings of the International
Conference on Quantum Criticality and Novel Phases (QCNP09, Dresden); subm.
to pss(b
Pressure effect on magnetic susceptibility of LaCoO
The effect of pressure on magnetic properties of LaCoO is studied
experimentally and theoretically. The pressure dependence of magnetic
susceptibility of LaCoO is obtained by precise measurements of
as a function of the hydrostatic pressure up to 2 kbar in the
temperature range from 78 K to 300 K. A pronounced magnitude of the pressure
effect is found to be negative in sign and strongly temperature dependent. The
obtained experimental data are analysed by using a two-level model and DFT+U
calculations of the electronic structure of LaCoO. In particular, the fixed
spin moment method was employed to obtain a volume dependence of the total
energy difference between the low spin and the intermediate spin
states of LaCoO. Analysis of the obtained experimental dependence
within the two-level model, as well as our DFT+U calculations, have revealed
the anomalous large decrease in the energy difference with increasing
of the unit cell volume. This effect, taking into account a thermal expansion,
can be responsible for the temperatures dependence of , predicting its
vanishing near room temperature.Comment: 7 pages, 9 figure
Сравнительное исследование защитных покрытий на термостойкость
Modern gas turbine engines operate under changing temperature loads. Therefore, one of the important characteristics of the protective coatings used on the turbine blades is their high resistance to the occurrence and development of cracks under mechanical and thermal loads. The applied effective systems of internal heat removal of the cooled turbine blades lead to an increase in their heat stress. At present, cracks arising from thermal fatigue are one of the common defects of the protective coatings used on turbine blades. The heat resistance of coatings at high temperatures is determined by three factors: the shape of the part on which the coating is applied, the thickness of the coating and the phase composition of the surface layers or the maximum aluminum content in the coating. Therefore, when choosing a protective coating for these operating conditions, it is important to know the impact of these factors on the thermal stability of the coating. The paper presents a comparative study of various coatings on their resistance to crack formation under cyclic temperature change. The dependence of the heat resistance of the considered coatings on the method of their application and phase-structural state is established. Especially valuable is the established mechanism of formation and propagation of thermal fatigue cracks depending on the phase composition of the initial coating. It is shown that the durability of protective coatings with cyclic temperature change depends on the chemical composition of the coating and the method of its formation. The dependence of the formation of thermal fatigue cracks on the samples with the coatings under study on the number of cycles of temperature change is established.Современные ГТД работают в условиях изменения температурных нагрузок, поэтому одной из важных характеристик применяемых защитных покрытий на рабочих лопатках турбины является их высокая сопротивляемость возникновению и развитию трещин при механических и термических нагрузках. Применяемые эффективные системы внутреннего теплоотвода охлаждаемых лопаток турбины приводят к росту их теплонапряженности. В настоящее время возникающие трещины от термической усталости являются одним из распространенных дефектов, применяемых на лопатках турбины защитных покрытий. Термостойкость покрытий при высоких температурах определяется тремя факторами: формой детали, на которую нанесено покрытие, толщиной покрытия и фазовым составом поверхностных слоев или максимальным содержанием алюминия в покрытии. Поэтому при выборе защитного покрытия для данных условий эксплуатации важно знать влияние данных факторов на термостойкость покрытия. В работе проведено сравнительное исследование различных покрытий на их стойкость к образованию трещин при циклическом изменении температуры. Установлена зависимость термостойкости рассматриваемых покрытий от метода их нанесения и фазово-структурного состояния. Особенно ценным является установленный механизм образования и распространения термоусталостных трещин в зависимости от фазового состава исходного покрытия. Показано, что долговечность защитных покрытий при циклическом изменении температуры зависит от химического состава покрытия и способа его формирования. Установлена зависимость образования термоусталостных трещин на образцах с исследуемыми покрытиями от количества циклов изменения температуры
Low temperature properties of the electron spin resonance in YbRh2Si2
We present the field and temperature behavior of the narrow electron spin resonance (ESR) response in YbRh2Si2 well below the single ion Kondo temperature. The ESR g-factor reflects a Kondo-like field and temperature evolution of the Yb* magnetism. Measurements toward low temperatures (> 0.5 K) have shown distinct crossover anomalies of the ESR parameters upon approaching the regime of a well-defined heavy Fermi liquid. Comparison with the field dependence of specific heat and electrical resistivity reveal that the ESR parameters can be related to quasiparticle mass and cross section and, hence, contain inherent heavy electron properties. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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