6,947 research outputs found
Spin-Wave Spectrum in `Single-Domain' Magnetic Ground State of Triangular Lattice Antiferromagnet CuFeO2
By means of neutron scattering measurements, we have investigated spin-wave
excitation in a collinear four-sublattice (4SL) magnetic ground state of a
triangular lattice antiferromagnet CuFeO2, which has been of recent interest as
a strongly frustrated magnet, a spin-lattice coupled system and a multiferroic.
To avoid mixing of spin-wave spectrum from magnetic domains having three
different orientations reflecting trigonal symmetry of the crystal structure,
we have applied uniaxial pressure on [1-10] direction of a single crystal
CuFeO2. By elastic neutron scattering measurements, we have found that only 10
MPa of the uniaxial pressure results in almost 'single domain' state in the 4SL
phase. We have thus performed inelastic neutron scattering measurements using
the single domain sample, and have identified two distinct spin- wave branches.
The dispersion relation of the upper spin-wave branch cannot be explained by
the previous theoretical model [R. S. Fishman: J. Appl. Phys. 103 (2008)
07B109]. This implies the importance of the lattice degree of freedom in the
spin-wave excitation in this system, because the previous calculation neglected
the effect of the spin-driven lattice distortion in the 4SL phase. We have also
discussed relationship between the present results and the recently discovered
"electromagnon" excitation.Comment: 5 pages, 3 figures, accepted for publication in J. Phys. Soc. Jp
A search for cyclotron resonance features with INTEGRAL
We present an INTEGRAL observation of the Cen-Crux region in order to search
the electron cyclotron resonance scattering features from the X-ray binary
pulsars. During the AO1 200ks observation, we clearly detected 4 bright X-ray
binaries, 1 Seyfert Galaxy, and 4 new sources in the field of view. Especially
from GX301-2, the cyclotron resonance feature is detected at about 37 keV, and
width of 3--4 keV. In addition, the depth of the resonance feature strongly
depends on the X-ray luminosity. This is the first detection of luminosity
dependence of the resonance depth. The cyclotron resonance feature is
marginally detected from 1E1145.1-6141. Cen X-3 was very dim during the
observation and poor statistics disable us to detect the resonance
features.These are first INTEGRAL results of searching for the cyclotron
resonance feature.Comment: 4pages, 8figures, To be published in the Proceedings of the 5th
INTEGRAL Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munic
Electric Polarization Induced by a Proper Helical Magnetic Ordering in a Delafossite Multiferroic CuFe1-xAlxO2
Multiferroic CuFe1-xAlxO2 (x=0.02) exhibits a ferroelectric ordering
accompanied by a proper helical magnetic ordering below T=7K under zero
magnetic field. By polarized neutron diffraction and pyroelectric measurements,
we have revealed a one-to-one correspondence between the spin helicity and the
direction of the spontaneous electric polarization. This result indicates that
the spin helicity of the proper helical magnetic ordering is essential for the
ferroelectricity in CuFe1-xAlxO2. The induction of the electric polarization by
the proper helical magnetic ordering is, however, cannot be explained by the
Katsura-Nagaosa-Balatsky model, which successfully explains the
ferroelectricity in the recently explored ferroelectric helimagnets, such as
TbMnO3. We thus conclude that CuFe1-xAlxO2 is a new class of magnetic
ferroelectrics.Comment: 4 pages, 4 figure
[OII]3727 Emission from the Companion to the Quasar BR 1202-0725 at z=4.7
Results of a narrow-band imaging for the redshifted [OII]3727 emission around
a quasar at z=4.7 obtained with the Subaru telescope and CISCO (a Cassegrain
near infrared camera) are presented. A significant emission line is detected in
the narrow-band H_2 (v=1-0 S(1)) filter at a location 2.4" northwest from the
quasar, where the presence of a companion has been reported in Lyman alpha
emission and the rest-frame UV continuum. We identify this line as [OII]3727
emission and confirm that the source really is a companion at z=4.7. The
[OII]3727 flux from the companion is estimated to be 2.5 x 10^{-17} erg s^{-1}
cm^{-2}. If the companion is a star forming object, the inferred star formation
rate is as high as 45-230 M_{solar} yr^{-1} even without assuming the
extinction correction. This value is higher than those derived from the Lyman
alpha emission or from the UV continuum. Thus, provided that the difference is
caused by dust extinction, the extinction corrected star formation rate is
calculated to be 45 to 2300 M_{solar} yr^{-1} depending on the assuming
extinction curves.Comment: 15 pages including 3 figures. Accepted for publication in PAS
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840
A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
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