1,102 research outputs found
Hierarchical geometric frustration in La3Cu2VO9
The crystallographic structure and magnetic properties of the La3Cu2VO9 were
investigated by powder neutron diffraction and magnetization measurements. The
compound materializes geometric frustration at two spatial scales, within
clusters and between clusters, and at different temperature scales. It is shown
by exactly solving the hamiltonian spectrum that collective spins are formed on
each clusters at low temperature before inter-clusters coupling operates.Comment: 6 pages, 4 figures. HFM2006 proceeding pape
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Inhomogeneous magnetism in the doped kagome lattice of LaCuO2.66
The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by
nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical
resistivity, bulk magnetization and specific heat measurements. For
temperatures above ~180 K, the spin and charge properties show an activated
behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the
results indicate an insulating ground state which may or may not be charge
ordered. While the frustrated spins in remaining patches of the original kagome
lattice might not be directly detected here, the observation of coexisting
non-magnetic sites, free spins and frozen moments reveals an intrinsically
inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice
rationalize this magnetic state in terms of a heterogeneous distribution of
cluster sizes and morphologies near the site-percolation threshold
Formation of collective spins in frustrated clusters
Using magnetization, specific heat and neutron scattering measurements, as
well as exact calculations on realistic models, the magnetic properties of the
\lacuvo compound are characterized on a wide temperature range. At high
temperature, this oxide is well described by strongly correlated atomic =1/2
spins while decreasing the temperature it switches to a set of weakly
interacting and randomly distributed entangled pseudo spins and
. These pseudo-spins are built over frustrated clusters, similar to
the kagom\'e building block, at the vertices of a triangular superlattice, the
geometrical frustration intervening then at different scales.Comment: 10 page
Pyrochlore Antiferromagnet: A Three-Dimensional Quantum Spin Liquid
The quantum pyrochlore antiferromagnet is studied by perturbative expansions
and exact diagonalization of small clusters. We find that the ground state is a
spin-liquid state: The spin-spin correlation functions decay exponentially with
distance and the correlation length never exceeds the interatomic distance. The
calculated magnetic neutron diffraction cross section is in very good agreement
with experiments performed on Y(Sc)Mn2. The low energy excitations are
singlet-singlet ones, with a finite spin gap.Comment: 4 pages, 4 figure
Hole-doping effects on a frustrated spin ladder
Hole-doping effects are investigated on the {\it t-J} ladder model with the
linked-tetrahedra structure. We discuss how a metal-insulator transition occurs
upon hole doping with particular emphasis on the effects of geometrical
frustration. By computing the electron density and the spin correlation
function by the density matrix renormalization group, we show that strong
frustration triggers a first-order transition to a metallic phase, when holes
are doped into the plaquette-singlet phase. By examining spin excitations in a
metallic case in detail, we discuss whether the spin-gap phase persists upon
hole doping according to the strength of frustration. It is further shown that
the lowest excited state in a spin-gap metallic phase can be described in two
independent quasiparticles.Comment: 7 pages, 9 figure
Deviations from aspirational target levels and environmental and safety performance:Implications for operations managers acting irresponsibly
Summary of OSQAR First Achievements and Main Requests for 2008
Abstract - In the first paragraph, OSQAR foremost achievements are summarised together with a brief reminder of its scientific context. In the second paragraph, activities planned for 2008 are briefly reviewed including the expected scientific results. The third paragraph is devoted to the requests addressed to CERN as the host laboratory and as a collaboration member of the OSQAR photon regeneration experiment
Toward Perfection: Kapellasite, Cu3Zn(OH)6Cl2, a New Model S = 1/2 Kagome Antiferromagnet
The search for the resonating valence bond (RVB) state continues to underpin
many areas of condensed matter research. The RVB is made from the dimerisation
of spins on different sites into fluctuating singlets, and was proposed by
Anderson to be the reference state from which the transition to BCS
superconductivity occurs. Little is known about the state experimentally, due
to the scarcity of model materials. Theoretical work has put forward the S =
1/2 kagome antiferromagnet (KAFM) as a good candidate for the realization of
the RVB state. In this paper we introduce a new model system, the S = 1/2 KAFM
Kapellasite, Cu3Zn(OH)6Cl2. We show that its crystal structure is a good
approximation to a 2-dimensional kagome antiferromagnet and that susceptibility
data indicate a collapse of the magnetic moment below T = 25 K that is
compatible with the spins condensing into the non-magnetic RVB state.Comment: Communication, 3 pages, 3 figure
Spin-fluctuations in the quarter-filled Hubbard ring : significances to LiVO
Using the quantum Monte Carlo method, we investigate the spin dynamics of
itinerant electrons in the one-dimensional Hubbard system. Based on the model
calculation, we have studied the spin-fluctuations in the quarter-filled
metallic Hubbard ring, which is aimed at the vanadium ring or chain defined
along corner-sharing tetrahedra of LiVO, and found the dramatic changes
of magnetic responses and spin-fluctuation characteristics with the
temperature. Such results can explain the central findings in the recent
neutron scattering experiment for LiVO.Comment: 5 pages, 3 figure
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