1,056 research outputs found
Amorphous ferromagnetism and re-entrant magnetic glassiness in SmMoO: new insights into the electronic phase diagram of pyrochlore molybdates
We discuss the magnetic properties of a SmMoO single
crystal as investigated by means of different experimental techniques. In the
literature, a conventional itinerant ferromagnetic state is reported for the
Mo sublattice below K. However, our results of dc
magnetometry, muon spin spectroscopy (SR) and high-harmonics magnetic
ac susceptibility unambiguously evidence highly disordered conditions in this
phase, in spite of the crystalline and chemical order. This disordered magnetic
state shares several common features with amorphous ferromagnetic alloys. This
scenario for SmMoO is supported by the anomalously high
values of the critical exponents, as mainly deduced by a scaling analysis of
our dc magnetization data and confirmed by the other techniques. Moreover,
SR detects a significant static magnetic disorder at the microscopic
scale. At the same time, the critical divergence of the third-harmonic
component of the ac magnetic susceptibility around K leads to
additional evidence towards the glassy nature of this magnetic phase. Finally,
the longitudinal relaxation of spin polarization (also supported by
results of ac susceptibility) evidences re-entrant glassy features similar to
amorphous ferromagnets.Comment: 15 pages, 13 figure
Orbital polaron lattice formation in lightly doped La1-xSrxMnO3
By resonant x-ray scattering at the Mn K-edge on La7/8Sr1/8MnO3, we show that
an orbital polaron lattice (OPL) develops at the metal-insulator transition of
this compound. This orbital reordering explains consistently the unexpected
coexistence of ferromagnetic and insulating properties at low temperatures, the
quadrupling of the lattice structure parallel to the MnO2-planes, and the
observed polarization and azimuthal dependencies. The OPL is a clear
manifestation of strong orbital-hole interactions, which play a crucial role
for the colossal magnetoresistance effect and the doped manganites in general
Ballistic heat transport of quantum spin excitations as seen in SrCuO2
Fundamental conservation laws predict ballistic, i.e., dissipationless
transport behaviour in one-dimensional quantum magnets. Experimental evidence,
however, for such anomalous transport has been lacking ever since. Here we
provide experimental evidence for ballistic heat transport in a S=1/2
Heisenberg chain. In particular, we investigate high purity samples of the
chain cuprate SrCuO2 and observe a huge magnetic heat conductivity
. An extremely large spinon mean free path of more than a
micrometer demonstrates that is only limited by extrinsic
scattering processes which is a clear signature of ballistic transport in the
underlying spin model
Magnetisation of hole-doped CuO2 spin chains in Sr14-xCaxCu24O41
We report on magnetisation measurements of Sr14-xCaxCu24O41, with 0 <= x <=
12, in magnetic fields up to 16 T. The low temperature magnetic response of the
CuO2 spin chains changes strongly upon doping. For x = 0, the ground state with
nearly independent dimers is confirmed. Reduction of the number of holes in the
chains through Ca-doping leads to an additional contribution to the
magnetisation, which depends linearly on the magnetic field. Remarkably, the
slope of this linear contribution increases with the Ca content. We argue that
antiferromagnetic spin chains do not account for this behaviour but that the
hole dynamics might be involved.Comment: In v2, spelling of author names has been change
Pseudogap and charge density waves in two dimensions
An interaction between electrons and lattice vibrations (phonons) results in
two fundamental quantum phenomena in solids: in three dimensions it can turn a
metal into a superconductor whereas in one dimension it can turn a metal into
an insulator. In two dimensions (2D) both superconductivity and charge-density
waves (CDW) are believed to be anomalous. In superconducting cuprates, critical
transition temperatures are unusually high and the energy gap may stay unclosed
even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the
resistivity below the transition can decrease with temperature even faster than
in the normal phase and a basic prerequisite for the CDW, the favourable
nesting conditions (when some sections of the Fermi surface appear shifted by
the same vector), seems to be absent. Notwithstanding the existence of
alternatives to conventional theories, both phenomena in 2D still remain the
most fascinating puzzles in condensed matter physics. Using the latest
developments in high-resolution angle-resolved photoemission spectroscopy
(ARPES) here we show that the normal-state pseudogap also exists in one of the
most studied 2D examples, dichalcogenide 2H-TaSe2, and the formation of CDW is
driven by a conventional nesting instability, which is masked by the pseudogap.
Our findings reconcile and explain a number of unusual, as previously believed,
experimental responses as well as disprove many alternative theoretical
approaches. The magnitude, character and anisotropy of the 2D-CDW pseudogap are
intriguingly similar to those seen in superconducting cuprates.Comment: 14 pages including figures and supplementary informatio
Revisiting the chain magnetism in Sr14Cu24O41: Experimental and numerical results
We study the magnetism of the hole doped CuO2 spin chains in Sr14Cu24O41 by
measuring the Electron Spin Resonance (ESR) and the static magnetization M in
applied magnetic fields up to 14 T. In this compound, the dimerized ground
state and the charge order in the chains are well established. Our experimental
data suggest that at low temperatures the Curie-like increase of M as well as
the occurrence of the related ESR signal are due to a small amount of
paramagnetic centers which are not extrinsic defects but rather unpaired Cu
spins in the chain. These observations qualitatively confirm recent ab initio
calculations of the ground state properties of the CuO2 chains in Sr14Cu24O41.
Our complementary quantum statistical simulations yield that the temperature
and field dependence of the magnetization can be well described by an effective
Heisenberg model in which the ground state configuration is composed of spin
dimers, trimers, and monomers.Comment: revised versio
Effect of external pressure on the magnetic properties of CoAsO ( = La, Pr, Sm): a SR study
We report on a detailed investigation of the itinerant ferromagnets LaCoAsO,
PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the
application of external hydrostatic pressures up to GPa. These
materials are shown to be magnetically hard in view of the weak dependence of
both critical temperatures and internal fields at the muon site on .
In the cases = La and Sm, the behaviour of the internal field is
substantially unaltered up to GPa. A much richer phenomenology is
detected in PrCoAsO instead, possibly associated with a strong dependence
of the statistical population of the two different crystallographic sites for
the muon. Surprisingly, results are notably different from what is observed in
the case of the isostructural compounds CoPO, where the full As/P
substitution is already inducing a strong chemical pressure within the lattice
but is still very effective in further affecting the magnetic properties.Comment: 8 pages, 9 figure
Plasmon Evolution and Charge-Density Wave Suppression in Potassium Intercalated Tantalum Diselenide
We have investigated the influence of potassium intercalation on the
formation of the charge-density wave (CDW) instability in 2H-tantalum
diselenide by means of Electron Energy-Loss Spectroscopy and density functional
theory. Our observations are consistent with a filling of the conduction band
as indicated by a substantial decrease of the plasma frequency in experiment
and theory. In addition, elastic scattering clearly points to a destruction of
the CDW upon intercalation as can be seen by a vanishing of the corresponding
superstructures. This is accompanied by a new superstructure, which can be
attributed to the intercalated potassium. Based on the behavior of the c-axis
upon intercalation we argue in favor of interlayer-sites for the alkali-metal
and that the lattice remains in the 2H-modification
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