286 research outputs found
Electric field control of multiferroic domains in NiVO imaged by X-ray polarization enhanced topography
The magnetic structure of multiferroic NiVO has been investigated
using non-resonant X-ray magnetic scattering. Incident circularly polarized
X-rays combined with full polarization analysis of the scattered beam is shown
to yield high sensitivity to the components of the cycloidal magnetic order,
including their relative phases. New information on the magnetic structure in
the ferroelectric phase is obtained, where it is found that the magnetic
moments on the "cross-tie" sites are quenched relative to those on the "spine"
sites. This implies that the onset of ferroelectricity is associated mainly
with spine site magnetic order. We also demonstrate that our technique enables
the imaging of multiferroic domains through polarization enhanced topography.
This approach is used to image the domains as the sample is cycled by an
electric field through its hysteresis loop, revealing the gradual switching of
domains without nucleation.Comment: 9 pages, 6 figure
Mammalian behavior and physiology converge to confirm sharper cochlear tuning in humans
Frequency analysis of sound by the cochlea is the most fundamental property of the auditory system. Despite its importance, the resolution of this frequency analysis in humans remains controversial. The controversy persists because the methods used to estimate tuning in humans are indirect and have not all been independently validated in other species. Some data suggest that human cochlear tuning is considerably sharper than that of laboratory animals, while others suggest little or no difference between species. We show here in a single species (ferret) that behavioral estimates of tuning bandwidths obtained using perceptual masking methods, and objective estimates obtained using otoacoustic emissions, both also employed in humans, agree closely with direct physiological measurements from single auditory-nerve fibers. Combined with human behavioral data, this outcome indicates that the frequency analysis performed by the human cochlea is of significantly higher resolution than found in common laboratory animals. This finding raises important questions about the evolutionary origins of human cochlear tuning, its role in the emergence of speech communication, and the mechanisms underlying our ability to separate and process natural sounds in complex acoustic environments
Resonant X-Ray Magnetic Scattering from CoO
We analyze the recent experiment [W. Neubeck {\em et al.}, Phys. Rev. B
\vol(60,1999,R9912)] for the resonant x-ray magnetic scattering (RXMS) around
the K edge of Co in the antiferromagnet CoO. We propose a mechanism of the RXMS
to make the states couple to the magnetic order: the intraatomic exchange
interaction between the and the states and the - mixing to the
states of neighboring Co atoms. These couplings induce the orbital moment
in the states and make the scattering tensor antisymmetric. Using a
cluster model, we demonstrate that this modification gives rise to a large RXMS
intensity in the dipole process, in good agreement with the experiment. We also
find that the pre-edge peak is generated by the transition to the states
in the quadrupole process, with negligible contribution of the dipole process.
We also discuss the azimuthal angle dependence of the intensity.Comment: 15 pages, 8 figure
Circularly polarised X-rays as a probe of non-collinear magnetic order in multiferroic TbMnO3
Non-resonant X-ray magnetic scattering has been used to study the magnetic
structure of multiferroic TbMnO3 in its ferroelectric phase. Circularly
polarized X-rays were combined with a full polarization analysis of the
scattered beam to reveal important new information on the magnetic structure of
this canonical multiferroic. An applied electric field is shown to create a
magnetic nearly mono-domain state in which the cylcoidal order on the Mn
sublattice rotates either clockwise or counter-clockwise depending on the sign
of the field. It is demonstrated how this technique provides sensitivity to the
absolute sense of rotation of the Mn moments, and to components of the ordering
on the Tb sublattice and phase shifts that earlier neutron diffraction
experiments could not resolve.Comment: 4 pages, 3 figure
Femtoscale magnetically induced lattice distortions in multiferroic TbMnO3
Magneto-electric multiferroics exemplified by TbMnO3 possess both magnetic
and ferroelectric long-range order. The magnetic order is mostly understood,
whereas the nature of the ferroelectricity has remained more elusive. Competing
models proposed to explain the ferroelectricity are associated respectively
with charge transfer and ionic displacements. Exploiting the magneto-electric
coupling, we use an electric field to produce a single magnetic domain state,
and a magnetic field to induce ionic displacements. Under these conditions,
interference charge-magnetic X-ray scattering arises, encoding the amplitude
and phase of the displacements. When combined with a theoretical analysis, our
data allow us to resolve the ionic displacements at the femtoscale, and show
that such displacements make a significant contribution to the zero-field
ferroelectric moment.Comment: This is the author's version of the work. It is posted here by
permission of the AAAS for personal use, not for redistribution. The
definitive version was published in Science VOL 333, (2011),
doi:10.1126/science.120808
Expression of Interest: The Atmospheric Neutrino Neutron Interaction Experiment (ANNIE)
Neutron tagging in Gadolinium-doped water may play a significant role in
reducing backgrounds from atmospheric neutrinos in next generation proton-decay
searches using megaton-scale Water Cherenkov detectors. Similar techniques
might also be useful in the detection of supernova neutrinos. Accurate
determination of neutron tagging efficiencies will require a detailed
understanding of the number of neutrons produced by neutrino interactions in
water as a function of momentum transferred. We propose the Atmospheric
Neutrino Neutron Interaction Experiment (ANNIE), designed to measure the
neutron yield of atmospheric neutrino interactions in gadolinium-doped water.
An innovative aspect of the ANNIE design is the use of precision timing to
localize interaction vertices in the small fiducial volume of the detector. We
propose to achieve this by using early production of LAPPDs (Large Area
Picosecond Photodetectors). This experiment will be a first application of
these devices demonstrating their feasibility for Water Cherenkov neutrino
detectors.Comment: Submitted for the January 2014 Fermilab Physics Advisory Committee
meetin
Expression of Interest: The Atmospheric Neutrino Neutron Interaction Experiment (ANNIE)
Submitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingNeutron tagging in Gadolinium-doped water may play a significant role in reducing backgrounds from atmospheric neutrinos in next generation proton-decay searches using megaton-scale Water Cherenkov detectors. Similar techniques might also be useful in the detection of supernova neutrinos. Accurate determination of neutron tagging efficiencies will require a detailed understanding of the number of neutrons produced by neutrino interactions in water as a function of momentum transferred. We propose the Atmospheric Neutrino Neutron Interaction Experiment (ANNIE), designed to measure the neutron yield of atmospheric neutrino interactions in gadolinium-doped water. An innovative aspect of the ANNIE design is the use of precision timing to localize interaction vertices in the small fiducial volume of the detector. We propose to achieve this by using early production of LAPPDs (Large Area Picosecond Photodetectors). This experiment will be a first application of these devices demonstrating their feasibility for Water Cherenkov neutrino detectors
Resonant X-Ray Scattering from CeB
We calculate the resonant x-ray scattering (RXS) spectra near the Ce absorption edge in CeB, on the basis of a microscopic model that the
states of Ce are atomic while the states form an energy band with a
reasonable density of states. In the initial state, we employ an effective
Hamiltonian of Shiina {\it et al}. in the antiferro-quadrupole (AFQ) ordering
phase, while we construct the wave function consistent with the neutron
scattering experiment in the magnetic ground state. In the intermediate state,
we take full account of the intra-atomic Coulomb interaction. Without assuming
any lattice distortion, we obtain sufficient RXS intensities on the AFQ
superlattice spot. We obtain the spectral shape, the temperature and magnetic
field dependences in good agreement with the experiment, thus demonstrating the
mechanism that the intensity is brought about by the modulation of states
through the anisotropic term of the - Coulomb interaction. In the
magnetic ground state, a small pre-edge peak is found by the process. On
the magnetic superlattice spot, we get a finite but considerably small
intensity. The magnetic form factor is briefly discussed.Comment: Latex, 10 pages, 12 figures. To be published in J. Phys. Soc. Jpn.,
Vol.71, No. 7 (2002
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