Однонаправленная анизотропия в планарных массивах нанопроволок железа: исследование методом ферромагнитного резонанса

Исследован ферромагнитный резонанс в планарных массивах нанопроволок (НП) железа, покрытых слоем MgO, в зависимости от времени старения. Планарные массивы НП Fe выращены на ступенчатой вицинальной поверхности окисленных подложек Si (111) методом малоугловой молекулярно-лучевой эпитаксии. С помощью методики ферромагнитного резонанса в данной системе обнаружена перпендикулярная однонаправленная анизотропия, которая становится более выраженной в процессе старения образцов. Сделан вывод, что причиной обнаруженных эффектов является окисление железа и формирование антиферромагнитных областей в окрестности интерфейса Fe/MgO.Досліджено феромагнітний резонанс у планарних масивах нанодротів (НД) заліза, які покриті шаром MgO, залежно від часу старіння. Планарні масиви НД Fe вирощено на ступінчастій віцинальній поверхні окиснених підкладок Si (111) методом малокутової молекулярно-променевої епітаксії. За допомогою методики феромагнітного резонансу в цій системі виявлено перпендикулярну однонапрямлену анізотропію, яка стає більш вираженою у процесі старіння зразків. Зроблено висновок, що причиною виявлених ефектів є окиснення заліза та формування антиферомагнітних областей поблизу інтерфейсу Fe/MgO.Ferromagnetic resonance in planar arrays of MgO capped iron nanowires (NW) has been studied as a function of sample aging time. The planar NW arrays were grown on a stepped vicinal surface of oxidized Si (111) substrates by means of low-angle molecular beam epitaxy. The ferromagnetic resonance measurements revealed a perpendicular unidirectional anisotropy, which became more pronounced with increasing the sample aging time. It is concluded that the observed effects originate from oxidation of iron and formationof antiferromagnetic regions in the vicinity of the Fe/MgO interface

The Growth of CdTe Layer on GaAs Substrate by MBE

We present the results of growth of CdTe layer on (013)GaAs substrate. The sequence processes include the preparation of GaAs surface by chemical etching and annealing in ultra-high vacuum, the growth of ZnTe layer on atomically clean GaAs surface and then the growth of CdTe layer on ZnTe/GaAs. All processes were carried out without removing GaAs substrate from MBE set. The processes were controlled by RHEED and single wavelength ellipsometry. We found that the evaporation of arsenic oxides and gallium oxides from the (001)GaAs surface were observed at over 400 and 500°C, respectively. The growth of CdTe on (001)GaAs leads to appearance of mixture orientations because of large mismatch of lattice parameters. We study the growth of ZnTe on (001)GaAs and (013)GaAs substrates to prevent the growth of mixture orientations. We study the influence of cadmium and tellurium ratio in molecular fluxes and temperature on the growth mechanism of ZnTe and CdTe, crystal perfection, surface roughness and defects density. The optimal condition for growth of high quality thick CdTe on GaAs substrate were found

Ferrimagnetism of the magnetoelectric compound Cu2OSeO3 probed by 77Se NMR

We present a thorough 77Se nuclear-magnetic-resonance (NMR) study of a single crystal of the magnetoelectric compound Cu 2OSeO3. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high- T paramagnetic phase to a low- T ferrimagnetic state with 3/4 of the Cu2+ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction in the crystal symmetry from its high- T cubic P 213 space group. These results are in agreement with high-resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos [Phys. Rev. B 78, 094416 (2008)]10.1103/PhysRevB.78.094416. We also develop a mean-field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic (Jafm ≃68 K) and one ferromagnetic (J fm ≃-50 K) nearest-neighbor exchange interaction. © 2010 The American Physical Society

Oxide nanotemplates for self-assembling "solid" building blocks

It is widely accepted that self-assembling building blocks is one of the promising ways for engineering new materials. Recent years reveal substantial progress in fabricating colloidal particles, polymer blocks and supramolecular aggregates of organic molecules. Despite of substantial progress in molecular self-assembly there is still a lack of simple blocks made of "solid matter" (e.g. metals, oxides etc.) with well-defined crystal structure and spatial order. Here we demonstrate that ordered arrays of metal nanoclusters can be fabricated by self-assembly on a wide range of oxide templates. These nano-templates are produced either by depositing an alien oxide film or by oxidizing a metal/metal oxide substrate.Comment: 11 pages, 2 figures added DFT calculations and Fig.

Magnetic properties of the magnetoelectric compound Cu2OSeO3: Magnetization and 77Se NMR study

We present magnetization and77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc≃ 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20-290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)]

The formation of complex chemical compounds in the spent fuel and their influence on separation processes

Some problems on formation of the complex chemical compounds (uranate, zirconate, etc.) in the fuel rods during irradiation and in oxidative reactions are considered. Complex compounds in uence the separation processes at magnetoplasma reprocessing of spent nuclear fuel (SNF). The variant of the experimental setup for simulating the processes of formation of complex compounds in the SNF is proposed.Розглянуто деякі проблеми, пов'язані з утворенням складних сполук (уранати, цирконати та ін.) у ТВЕЛ-ах при опроміненні та в окисних реакціях, які впливають на сепараційні процеси при магнітоплазмовій переробці ВЯП. Запропоновано варіант експериментальної установки для імітації процесів утворення складних сполук у ВЯП.Рассмотрены некоторые проблемы, связанные с образованием сложных соединений (уранаты, цирконаты и др.) в ТВЭЛ-ах при облучении и в окислительных реакциях, которые влияют на сепарационные процессы при магнитоплазменной переработке ОЯТ. Предложен вариант экспериментальной установки для имитации процессов образования сложных соединений в ОЯТ

Influence of exogenous lactoferrin on the oxidant/ antioxidant balance and molecular profile of hormone receptor-positive and -negative human breast cancer cells in vitro

Aim: To investigate the mechanisms of cytotoxic activity and pro-/antioxidant effect of lactoferrin on hormone receptor-positive and receptor-negative breast cancer cells in vitro. Materials and Methods: The study was performed on receptor-positive (MCF-7, T47D) and receptor-negative (MDA-MB-231, MDA-MB-468) human breast cancer cell lines. Immunocytochemical staining, flow cytometry, low-temperature electron paramagnetic resonance, and the Comet assay were used. Results: Upon treatment with lactoferrin, the increased levels of reactive oxygen species (ROS) (p < 0.05), NO generation rate by inducible NO-synthase (p < 0.05) and the level of “free” iron (p < 0.05) were observed. Moreover, the effects of lactoferrin were more pronounced in receptor-negative MDA-MB-231 and MDA-MB-468 cells. These changes resulted in increased expression of proapoptotic Bax protein (p < 0.05), reduced expression of the antiapoptotic Bcl-2 protein (p < 0.05) and level of not-oxidized mitochondrial cardiolipin (1.4–1.7-fold, p < 0.05). This, in turn, caused an increase in the percentage of apoptotic cells (by 14–24%, p < 0.05). Cytotoxic effects of lactoferrin were accompanied by an increase in the percentage of DNA in the comet tail and blocking cell cycle at G₂/M phase, especially in receptor-negative cell lines. Conclusion: The study showed that exogenous lactoferrin causes a violation of an antioxidant balance by increasing the level of ROS, “free” iron and NO generation rate, resalting in the blocking of cell cycle at G₂/M-phase and apoptosis of malignant cells