192 research outputs found
Magnetic structure of Ba(TiO)Cu(PO) probed using spherical neutron polarimetry
The antiferromagnetic compound Ba(TiO)Cu(PO) contains square
cupola of corner-sharing CuO plaquettes, which were proposed to form
effective quadrupolar order. To identify the magnetic structure, we have
performed spherical neutron polarimetry measurements. Based on symmetry
analysis and careful measurements we conclude that the orientation of the
Cu spins form a non-collinear in-out structure with spins approximately
perpendicular to the CuO motif. Strong Dzyaloshinskii-Moriya interaction
naturally lends itself to explain this phenomenon. The identification of the
ground state magnetic structure should serve well for future theoretical and
experimental studies into this and closely related compounds.Comment: 9 pages, 4 figure
-cation control of magnetoelectric quadrupole order in (TiO)Cu(PO) ( = Ba, Sr, and Pb)
Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric
activity is discovered in the novel compound (TiO)Cu(PO) with
= Pb, which is in contrast with antiferroic quadrupole order observed in
the isostructural compounds with = Ba and Sr. Unlike the famous lone-pair
stereochemical activity which often triggers ferroelectricity as in PbTiO,
the Pb cation in Pb(TiO)Cu(PO) is stereochemically inactive
but dramatically alters specific magnetic interactions and consequently
switches the quadrupole order from antiferroic to ferroic. Our first-principles
calculations uncover a positive correlation between the degree of -O bond
covalency and a stability of the ferroic quadrupole order.Comment: 7 pages, 4 figure
Spinon localization in the heat transport of the spin-1/2 ladder compound (CHN)CuBr
We present experiments on the magnetic field-dependent thermal transport in
the spin-1/2 ladder system (CHN)CuBr. The thermal
conductivity is only weakly affected by the field-induced
transitions between the gapless Luttinger-liquid state realized for and the gapped states, suggesting the absence of a direct
contribution of the spin excitations to the heat transport. We observe,
however, that the thermal conductivity is strongly suppressed by the magnetic
field deeply within the Luttinger-liquid state. These surprising observations
are discussed in terms of localization of spinons within finite ladder segments
and spinon-phonon umklapp scattering of the predominantly phononic heat
transport.Comment: 4 pages, 3 figure
Chromium at High Pressures: Weak Coupling and Strong Fluctuations in an Itinerant Antiferromagnet
The spin- and charge-density-wave order parameters of the itinerant
antiferromagnet chromium are measured directly with non-resonant x-ray
diffraction as the system is driven towards its quantum critical point with
high pressure using a diamond anvil cell. The exponential decrease of the spin
and charge diffraction intensities with pressure confirms the harmonic scaling
of spin and charge, while the evolution of the incommensurate ordering vector
provides important insight into the difference between pressure and chemical
doping as means of driving quantum phase transitions. Measurement of the charge
density wave over more than two orders of magnitude of diffraction intensity
provides the clearest demonstration to date of a weakly-coupled, BCS-like
ground state. Evidence for the coexistence of this weakly-coupled ground state
with high-energy excitations and pseudogap formation above the ordering
temperature in chromium, the charge-ordered perovskite manganites, and the blue
bronzes, among other such systems, raises fundamental questions about the
distinctions between weak and strong coupling.Comment: 11 pages, 9 figures (8 in color
The J_{eff}=1/2 insulator Sr3Ir2O7 studied by means of angle-resolved photoemission spectroscopy
The low-energy electronic structure of the J_{eff}=1/2 spin-orbit insulator
Sr3Ir2O7 has been studied by means of angle-resolved photoemission
spectroscopy. A comparison of the results for bilayer Sr3Ir2O7 with available
literature data for the related single-layer compound Sr2IrO4 reveals
qualitative similarities and similar J_{eff}=1/2 bandwidths for the two
materials, but also pronounced differences in the distribution of the spectral
weight. In particuar, photoemission from the J_{eff}=1/2 states appears to be
suppressed. Yet, it is found that the Sr3Ir2O7 data are in overall better
agreement with band-structure calculations than the data for Sr2IrO4.Comment: 5 pages, 3 figure
Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu(PO) with CuO square cupolas
In vortex-like spin arrangements, multiple spins can combine into emergent
multipole moments. Such multipole moments have broken space-inversion and
time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME)
activity. Three types of such multipole moments are known: toroidal, monopole,
and quadrupole moments. So far, however, the ME-activity of these multipole
moments has only been established experimentally for the toroidal moment. Here,
we propose a magnetic square cupola cluster, in which four corner-sharing
square-coordinated metal-ligand fragments form a noncoplanar buckled structure,
as a promising structural unit that carries an ME-active multipole moment. We
substantiate this idea by observing clear magnetodielectric signals associated
with an antiferroic ME-active magnetic quadrupole order in the real material
Ba(TiO)Cu(PO). The present result serves as a useful guide for
exploring and designing new ME-active materials based on vortex-like spin
arrangements.Comment: 4 figure
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