62 research outputs found
Electronic structure and magnetic properties of the spin-1/2 Heisenberg system CuSe2O5
A microscopic magnetic model for the spin-1/2 Heisenberg chain compound
CuSe2O5 is developed based on the results of a joint experimental and
theoretical study. Magnetic susceptibility and specific heat data give evidence
for quasi-1D magnetism with leading antiferromagnetic (AFM) couplings and an
AFM ordering temperature of 17 K. For microscopic insight, full-potential DFT
calculations within the local density approximation (LDA) were performed. Using
the resulting band structure, a consistent set of transfer integrals for an
effective one-band tight-binding model was obtained. Electronic correlations
were treated on a mean-field level starting from LDA (LSDA+U method) and on a
model level (Hubbard model). In excellent agreement of experiment and theory,
we find that only two couplings in CuSe2O5 are relevant: the nearest-neighbour
intra-chain interaction of 165 K and a non-frustrated inter-chain coupling of
20 K. From a comparison with structurally related systems (Sr2Cu(PO4)2,
Bi2CuO4), general implications for a magnetic ordering in presence of
inter-chain frustration are made.Comment: 20 pages, 8 figures, 3 table
First-order structural transition in the magnetically ordered phase of Fe1.13Te
Specific heat, resistivity, magnetic susceptibility, linear thermal expansion
(LTE), and high-resolution synchrotron X-ray powder diffraction investigations
of single crystals Fe1+yTe (0.06 < y < 0.15) reveal a splitting of a single,
first-order transition for y 0.12. Most
strikingly, all measurements on identical samples Fe1.13Te consistently
indicate that, upon cooling, the magnetic transition at T_N precedes the
first-order structural transition at a lower temperature T_s. The structural
transition in turn coincides with a change in the character of the magnetic
structure. The LTE measurements along the crystallographic c-axis displays a
small distortion close to T_N due to a lattice striction as a consequence of
magnetic ordering, and a much larger change at T_s. The lattice symmetry
changes, however, only below T_s as indicated by powder X-ray diffraction. This
behavior is in stark contrast to the sequence in which the phase transitions
occur in Fe pnictides.Comment: 6 page
«MEMORYI» OF TSAR PITER (About collections time of Piter in funds National museum of Karelia Republic)
Статья посвящена раритетному собранию петровского времени, из фондов Национального музея Республики Карелия. Это продукция Петровского завода: чугунные артиллерийские орудия, ядра, мирские «била», вериги для «умерщвления плоти», цилиндрические печи. Значительная часть предметов относится к памятникам Поморского круга, включая образцы «мелкой пластики». Интересны памятные чугунные плиты Г.В. Геннина об открытии лечебного источника и строительстве дворца Петра I в Марциальных водах, первом российском курорте. Особо отметим нумизматическое собрание, которое включает медные и серебряные монеты чекана России и Голландской Республики.The article is devoted (dedicated) to the rare collection of the time of Peter the Great from the funds of the National Museum of the Republic of Karelia. These are the products of the Petrovsky Plant: cast-iron artillery pieces, cannonballs, mundane “beats”, chains for “mortification of the flesh”, cylindrical furnaces. A significant part of the objects belongs to the Pomeranian circle, including samples of “small plastic art”. The commemorative cast-iron plates by G.V. Gennin about the discovery of a healing spring and the construction of the palace of Peter the Great in the Marcial Waters, the first Russian resort, are of interest. We especially note the numismatic collection, which includes copper and silver coins minted in Russia and the Dutch Republic
Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5
Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical
vapour transport. While their thermodynamic and transport properties are
typical for ordinary metals, the electrical resistivity exhibits a shallow
minimum at low temperatures. Application of strong magnetic fields does not
influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5
apparently originates from interaction between the conduction electrons and
structural two-level systems. Significant disorder in the As-Se substructure is
inferred from X-ray diffraction and electron microprobe studies
Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure
The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides
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