216 research outputs found
Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in orthorhombic DyMnO3
Synchrotron x-ray diffraction and resonant magnetic scattering experiments on
single crystal DyMnO3 have been carried out between 4 and 40 K. Below TN(Dy) =
5K, the Dy magnetic moments order in a commensurate structure with propagation
vector 0.5 b*. Simultaneous with the Dy magnetic ordering, an incommensurate
lattice modulation with propagation vector 0.905 b* evolves while the original
Mn induced modulation is suppressed and shifts from 0.78 b* to 0.81 b*. This
points to a strong interference of Mn and Dy induced structural distortions in
DyMnO3 besides a magnetic coupling between the Mn and Dy magnetic moments.Comment: submitted to Phys. Rev. B Rapid Communication
Valence modulations in CeRuSn
CeRuSn exhibits an extraordinary room temperature structure at 300~K with
coexistence of two types of Ce ions, namely trivalent Ce and
intermediate valent Ce, in a metallic environment. The ordered
arrangement of these two Ce types on specific crystallographic sites results in
a doubling of the unit cell along the -axis with respect to the basic
monoclinic CeCoAl-type structure. Below room temperature, structural modulation
transitions with very broad hysteresis have been reported from measurements of
various bulk properties. X-ray diffraction revealed that at low temperatures
the doubling of the CeCoAl type structure is replaced by a different modulated
ground state, approximating a near tripling of the basic CeCoAl cell. The
transition is accompanied by a significant contraction of the axis. We
present new x-ray absorption near-edge spectroscopy data at the Ce L
absorption edge, measured on a freshly cleaved surface of a CeRuSn single
crystal. In contrast to a previous report, the new data exhibit small but
significant variations as function of temperature that are consistent with a
transition of a fraction of Ce ions to the intermediate valence state,
analogous to the transition in elemental cerium,
when cooling through the structural transitions of CeRuSn. Such results in a
valence-modulated state
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53
Synchrotron X-ray diffraction investigations of two single crystals of
Na_xCoO_2 from different batches with composition x = 0.525-0.530 reveal
homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53
0) at room-temperature. The incommensurate (qq0) superstructure exists between
220 K and 430 K. The value of q varies between q = 0.514 and 0.529, showing a
broad plateau at the latter value between 260 K and 360 K. On cooling, unusual
reversible phase segregation into two volume fractions is observed. Below 220
K, one volume fraction shows the well-known commensurate orthorhombic x = 0.50
superstructure, while a second volume fraction with x = 0.55 exhibits another
commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell.
We argue that the commensurate-to-incommensurate transition is an intrinsic
feature of samples with Na concentrations x = 0.5 + d with d ~ 0.03.Comment: Corrected/improved versio
Valence change of praseodymium in Pr0.5Ca0.5CoO3 investigated by x-ray absorption spectroscopy
X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 were performed
at the Pr M4,5, Pr L3, and Ca L2,3 absorption edges as a function of
temperature below 300 K. Ca spectra show no changes down to 10 K while a
noticeable thermally dependent evolution takes place at the Pr edges across the
metal-insulator transition. Spectral changes are analyzed by different methods,
including multiple scattering simulations, which provide quantitative details
on an electron loss at Pr 4f orbitals. We conclude that in the insulating phase
a fraction [15(+5)%] of Pr3+ undergoes a further oxidation to adopt a
hybridized configuration composed of an admixture of atomic-like 4f1 states
(Pr4+) and f- symmetry states on the O 2p valence band (Pr3+L states)
indicative of a strong 4f- 2p interaction.Comment: 19 pages (.doc), 4 figures, Phys. Rev. B, in pres
Observation of a valence transition in (Pr,Ca)CoO3 cobaltites: charge migration at the metal-insulator transition
X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 and
(Pr,Y)0.55Ca0.45CoO3 compositions reveal that the valence of praseodymium ions
is stable and essentially +3 (Pr [4f 2]) in the metallic state, but abruptly
changes when carriers localize approaching the oxidation state +4 (Pr [4f 1]).
This mechanism appears to be the driving force of the metal-insulator
transition. The ground insulating state of Pr0.5Ca0.5CoO3 is an homogeneous
Co3.5-d state stabilized by a charge transfer from Pr to Co sites: 1/2Pr3+ +
Co3.5 \to 1/2Pr3+2d + Co3.5-d, with 2d \approx 0.26 e-.Comment: Submitted. 14 pages, 4 Figure
Magnetic order in GdMnO3 in magnetic fields
Resonant magnetic x ray scattering at the Gd L2 edge is used to investigate the magnetic order of the Gd moments in multiferroic GdMnO3 at low temperatures. We present high magnetic field data on the magnetic ordering of Gd in the ferroelectric phase of GdMnO3. Our findings reaffirm the important role of the Gd moments in the symmetric magnetic exchange striction responsible for ferroelectricity in this compoun
Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO3
Ga for Mn substitution in multiferroic TbMnO has been performed in
order to study the influence of Mn-magnetic ordering on the Tb-magnetic
sublattice. Complete characterization of TbMnGaO ( = 0,
0.04, 0.1) samples, including magnetization, impedance spectroscopy, and x-ray
resonant scattering and neutron diffraction on powder and single crystals has
been carried out. We found that keeping the same crystal structure for all
compositions, Ga for Mn substitution leads to the linear decrease of and , reflecting the reduction of the exchange
interactions strength and the change of the Mn-O-Mn bond
angles. At the same time, a strong suppression of both the induced and the
separate Tb-magnetic ordering has been observed. This behavior unambiguously
prove that the exchange fields have a strong influence on the
Tb-magnetic ordering in the full temperature range below
and actually stabilize the Tb-magnetic ground state.Comment: 9 pages, 8 figure
Coupling of frustrated Ising spins to magnetic cycloid in multiferroic TbMnO3
We report on diffraction measurements on multiferroic TbMnO3 which
demonstrate that the Tb- and Mn-magnetic orders are coupled below the
ferroelectric transition TFE = 28 K. For T < TFE the magnetic propagation
vectors (tau) for Tb and Mn are locked so that tauTb = tauMn, while below TNTb
= 7 K we find that tauTb and tauMn lock-in to rational values of 3/7 b* and 2/7
b*, respectively, and obey the relation 3tauTb - tauMn = 1. We explain this
novel matching of wave vectors within the frustrated ANNNI model coupled to a
periodic external field produced by the Mn-spin order. The tauTb = tauMn
behavior is recovered when Tb magnetization is small, while the tauTb = 3/7
regime is stabilized at low temperatures by a peculiar arrangement of domain
walls in the ordered state of Ising-like Tb spins.Comment: 5 pages, 3 figure
Simple platelet markers: Mean platelet volume and congestive heart failure coexistent with periodontal disease. Pilot studies
Background: Conducted pilot study concerning mean platelet volume (MPV) parameter among patients suffering from congestive heart failure and periodontal disease.
Methods: Examination of dynamic changes of platelet and periodontal markers in group of 50 patients before and an average of 6 months subsequent to professional periodontal treatment.
Results: Both platelet and periodontal parameters decreased after periodontal treatment, what is more, the decrease of MPV value due to periodontal disease/mm improvement was shown to be statistically significant (p = 0.05).
Conclusions: Improvement of periodontal status may influence decrease of MPV value and increase of congestive heart failure treatment efficacy and effect patient comfort. It is a new, not frequently used pattern of chronic disease treatment optimalization
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