1,068 research outputs found
Commensurate Fluctuations in the Pseudogap and Incommensurate spin-Peierls Phases of TiOCl
X-ray scattering measurements on single crystals of TiOCl reveal the presence
of commensurate dimerization peaks within both the incommensurate spin-Peierls
phase and the so-called pseudogap phase above T_c2. This scattering is
relatively narrow in Q-space indicating long correlation lengths exceeding ~
100 A below T* ~ 130 K. It is also slightly shifted in Q relative to that of
the commensurate long range ordered state at the lowest temperatures, and it
coexists with the incommensurate Bragg peaks below T_c2. The integrated
scattering over both commensurate and incommensurate positions evolves
continuously with decreasing temperature for all temperatures below T* ~ 130 K.Comment: To appear in Physical Review B: Rapid Communications. 5 page
Suppression of the commensurate spin-Peierls state in Sc-doped TiOCl
We have performed x-ray scattering measurements on single crystals of the
doped spin-Peierls compound Ti(1-x)Sc(x)OCl (x = 0, 0.01, 0.03). These
measurements reveal that the presence of non-magnetic dopants has a profound
effect on the unconventional spin-Peierls behavior of this system, even at
concentrations as low as 1%. Sc-doping suppresses commensurate fluctuations in
the pseudogap and incommensurate spin-Peierls phases of TiOCl, and prevents the
formation of a long-range ordered spin-Peierls state. Broad incommensurate
scattering develops in the doped compounds near Tc2 ~ 93 K, and persists down
to base temperature (~ 7 K) with no evidence of a lock-in transition. The width
of the incommensurate dimerization peaks indicates short correlation lengths on
the order of ~ 12 angstroms below Tc2. The intensity of the incommensurate
scattering is significantly reduced at higher Sc concentrations, indicating
that the size of the associated lattice displacement decreases rapidly as a
function of doping.Comment: 7 pages, 5 figure
Hands-on Materials for Teaching about Global Climate Change through Graph Interpretation
Teachers need to address global climate change with students in their classrooms as evidence for consequences from these environmental changes mounts. One way to approach global climate change is through examination of authentic data. Mathematics and science may be integrated by interpreting graphs from the professional literature. This study examined the types of errors 72 preservice elementary teachers made in producing hands-on materials for teaching graph interpretation skills through graphed evidence of global climate change from the literature. The teaching materials consisted of a graph electronically manipulated on a colored background and enhanced with clip art related to the graph’s topic that was then printed and mounted on colored cardboard. The graph was accompanied by six graph interpretation statements printed on cards that were to be sorted as true or false. Additionally, a topic-related object was provided for each graph for an initial activity that focused student attention and aroused interest. Four graphs with their accompanying statements and four related objects were combined into one box of materials to be used by a small group of students. Preservice teachers practiced with example sets of materials made by the course instructor and then worked to each create a new, unique set. An appendix of many sets of correct materials is provided in this ERIC document. About half of the teaching materials produced were errorfree. The most common errors preservice teachers made were misuse of vocabulary and over generalizing a graph’s information. Other frequent errors included not supplying enough specific information in a statement to allow its verification and misinterpreting a major trend on a graph. These problems can be attributed to preservice teachers’ lack of sufficient experience in graph interpretation. Therefore, the authors conclude that the materials-making exercise was beneficial to preservice teachers and the resulting materials (with any errors corrected) can effectively be used with upper elementary and secondary students. [1 Table, 1 Appendix containing 18 graphs accompanied by interpretation statements.
Nature of the spin dynamics and 1/3 magnetization plateau in azurite
We present a specific heat and inelastic neutron scattering study in magnetic
fields up into the 1/3 magnetization plateau phase of the diamond chain
compound azurite Cu(CO)(OH). We establish that the
magnetization plateau is a dimer-monomer state, {\it i.e.}, consisting of a
chain of monomers, which are separated by dimers on the
diamond chain backbone. The effective spin couplings K
and K are derived from the monomer and dimer
dispersions. They are associated to microscopic couplings K,
K and a ferromagnetic K, possibly as
result of orbitals in the Cu-O bonds providing the superexchange
pathways.Comment: 5 pages, 4 figure
Critical X-ray Scattering Studies of Jahn-Teller Phase Transitions in TbVAsO
The critical behaviour associated with cooperative Jahn-Teller phase
transitions in TbVAsO (where \textit{x} = 0, 0.17, 1)
single crystals have been studied using high resolution x-ray scattering. These
materials undergo continuous tetragonal orthorhombic structural phase
transitions driven by Jahn-Teller physics at T = 33.26(2) K, 30.32(2) K and
27.30(2) K for \textit{x} = 0, 0.17 and 1 respectively. The orthorhombic strain
was measured close to the phase transition and is shown to display mean field
behavior in all three samples. Pronounced fluctuation effects are manifest in
the longitudinal width of the Bragg scattering, which diverges as a power law,
with an exponent given by , on approaching the transition from
either above or below. All samples exhibited twinning; however the disordered x
= 0.17 sample showed a broad distribution of twins which were stable to
relatively low temperatures, well below T. This indicates that while the
orthorhombic strain continues to develop in a conventional mean field manner in
the presence of disorder, twin domains are easily pinned by the quenched
impurities and their associated random strains.Comment: 8 pages, 6 figure
Structural Fluctuations in the Spin Liquid State of Tb2Ti2O7
High resolution X-ray scattering measurements on single crystal Tb2Ti2O7
reveal finite structural correlations at low temperatures. This geometrically
frustrated pyrochlore is known to exhibit a spin liquid, or cooperative
paramagnetic state, at temperatures below ~ 20 K. Parametric studies of
structural Bragg peaks appropriate to the Fdm space group of Tb2Ti2O7
reveal substantial broadening and peak intensity reduction in the temperature
regime 20 K to 300 mK. We also observe a small, anomalous lattice expansion on
cooling below a density maximum at ~ 18 K. These measurements are consistent
with the development of fluctuations above a cooperative Jahn-Teller,
cubic-tetragonal phase transition at very low temperatures.Comment: 5 pages, 4 figures, submitted for publicatio
Magnetoelastic and structural properties of azurite Cu3(CO3)2(OH)2 from neutron scattering and muon spin rotation
Azurite, Cu3(CO3)2(OH)2, has been considered an ideal example of a
one-dimensional (1D) diamond chain antiferromagnet. Early studies of this
material imply the presence of an ordered antiferromagnetic phase below K while magnetization measurements have revealed a 1/3 magnetization
plateau. Until now, no corroborating neutron scattering results have been
published to confirm the ordered magnetic moment structure. We present recent
neutron diffraction results which reveal the presence of commensurate magnetic
order in azurite which coexists with significant magnetoelastic strain. The
latter of these effects may indicate the presence of spin frustration in zero
applied magnetic field. Muon spin rotation, SR, reveals an onset of
short-range order below 3K and confirms long-range order below .Comment: 5 pages, 4 figures, PHYSICAL REVIEW B 81, 140406(R) (2010
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