Structure and magnetic order in Fe2+xV1-xAl

We present a detailed structural investigation via neutron diffraction of differently heat treated samples Fe2VAl and Fe2+xV1-xAl. Moreover, the magnetic behaviour of these materials is studied by means of mSR and Mossbauer-experiments. Our structural investigation indicates that quenched Fe2VAl, exhibiting the previously reported "Kondo insulating like" behaviour, is off-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is structurally better ordered and stoichiometric, and the microscopic magnetic probes establish long range ferromagnetic order below TC = 13K, consistent with results from bulk experiments. The magnetic state can be modelled as being generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively, the required number of magnetic ions is too large as to be explained by a model of Fe/V site exchange. We discuss the implications of our findings for the ground state properties of Fe2VAl, in particular with respect to the role of crystallographic disorder.Comment: accepted for publication in J. Phys.: Condens. Matte

Local structure determination in helimagnetic Co8Zn8Mn4 xFex

We have carried out a structural and magnetic characterization of Co8Zn8+y Mn4−y−x Fex by means of bulk techniques, powder neutron scattering and Mössbauer spectroscopy. From our data, we derive the main magnetic parameters and carry out a detailed structural characterization.Weobserve that disorder is present in our samples in various forms and that this seems to be generic for this class of materials. However, the disorder appears to have little impact on the character of the magnetic phases, and thus seems to be of no relevance for the skyrmionic phases established for these types of materials

Weak ferromagnetism with very large canting in a chiral lattice: (pyrimidine)2FeCl2

The transition metal coordination compound (pyrimidine)2FeCl2 crystallizes in a chiral lattice, space group I 4_1 2 2 (or I4_3 2 2). Combined magnetization, Mossbauer spectroscopy and powder neutron diffraction studies reveal that it is a canted antiferromagnet below T_N = 6.4 K with an unusually large canting of the magnetic moments of 14 deg. from their general antiferromagnetic alignment, one of the largest reported to date. This results in weak ferromagnetism with a ferromagnetic component of 1 mu_B. The large canting is due to the interplay between the antiferromagnetic exchange interaction and the local single-ion anisotropy in the chiral lattice. The magnetically ordered structure of (pyrimidine)2FeCl2, however, is not chiral. The implications of these findings for the search of molecule based materials exhibiting chiral magnetic ordering is discussed.Comment: 6 pages, 5 figure

Организация самостоятельных физкультурно-оздоровительных занятий "Программа 100 минут"

Подготовлено в помощь студентам, осваивающим теоретический курс дисциплины «Физическое воспитание», в том числе и студентам, освобожденным от практических занятий по «Физическому воспитанию». Назначение учебного пособия заключается в том, чтобы представить сведения, необходимые для разработки студентами индивидуальных физкультурно- оздоровительных программ.Содержит знания об использовании различных средств рекреационной физической культуры, самомассажа, а также психологических средств восстановления и самоконтроля за своим функциональным состоянием. Усвоив их, студенты могут под контролем преподавателя разрабатывать такие оздоровительные программы занятий, которые будут учитывать исходное состояние здоровья и способствовать достижению стойкой ремиссии в ходе преодоления имеющихся заболеваний

КЛАВИАТУРНЫЕ ШПИОНЫ

В данной работе приводится обзор клавиатурного шпионажа как одного из главных видов электронного мошенничества. Описана его «легальная» сторона и рассмотрены способы распространения. Так же приведены некоторые рекомендации защиты как от программных, так и от аппаратных клавиатурных шпионов

Solid-State Kinetic Investigations of Nonisothermal Reduction of Iron Species Supported on SBA-15

Iron oxide catalysts supported on nanostructured silica SBA-15 were synthesized with various iron loadings using two different precursors. Structural characterization of the as-prepared FexOy/SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, DR-UV-Vis spectroscopy, and Mössbauer spectroscopy. An increasing size of the resulting iron species correlated with an increasing iron loading. Significantly smaller iron species were obtained from (Fe(III), NH4)-citrate precursors compared to Fe(III)-nitrate precursors. Moreover, smaller iron species resulted in a smoother surface of the support material. Temperature-programmed reduction (TPR) of the FexOy/SBA-15 samples with H2 revealed better reducibility of the samples originating from Fe(III)-nitrate precursors. Varying the iron loading led to a change in reduction mechanism. TPR traces were analyzed by model-independent Kissinger method, Ozawa, Flynn, and Wall (OFW) method, and model-dependent Coats-Redfern method. JMAK kinetic analysis afforded a one-dimensional reduction process for the FexOy/SBA-15 samples. The Kissinger method yielded the lowest apparent activation energy for the lowest loaded citrate sample (Ea ≈ 39 kJ/mol). Conversely, the lowest loaded nitrate sample possessed the highest apparent activation energy (Ea ≈ 88 kJ/mol). For samples obtained from Fe(III)-nitrate precursors, Ea decreased with increasing iron loading. Apparent activation energies from model-independent analysis methods agreed well with those from model-dependent methods. Nucleation as rate-determining step in the reduction of the iron oxide species was consistent with the Mampel solid-state reaction model

Mössbauer studies on the Fe(II) oxalate spin ladder Na2Fe2(C2O4)(3)(H2O)(2)

We investigated the magnetic correlations in the Fe spin ladder system Na2Fe2(C2O4)(3)(H2O)(2) by magnetic susceptibility and Fe-57 Mossbauer spectroscopy between 2 and 310 K. The susceptibility exhibits a broad maximum at about 20 K indicating antiferromagnetic coupling and a S = 0 dimer formation. The Mossbauer measurements reveal a temperature dependent quadrupole splitting and a non-magnetic ground state. The orbital ground state is identified as a singlet with an excited doublet at 383 K in the T-2g manifold

Le virus de la grippe (de l'antiquité à nos jours)

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