2,056 research outputs found
Suppression of Magnetic Order by Pressure in BaFe2As2
We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2
under high pressure. The T-P phase diagram of BaFe2As2 determined from
resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly
is quite robust against P.Comment: 2 pages, 2 figure
Magnetic anisotropy of the spin ice compound Dy2Ti2O7
We report magnetization and ac susceptibility of single crystals of the spin
ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes
[100] and [110] agree with the expected values for an effective ferromagnetic
nearest-neighbor Ising pyrochlore with local anisotropy, where each
magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic
fields along the [111] axis, the saturated moment exhibits a beaking of the
ice-rule; it agrees with the value expected for a three-in one-out spin
configuration. Assuming the realistic magnetic interaction between Dy ions
given by the dipolar spin ice model, we completely reproduce the results at 2 K
by Monte Carlo calculations. However, down to at least 60 mK, we have not found
any experimental evidence of the long-range magnetic ordering predicted by this
model to occur at around 180 mK. Instead, we confirm the spin freezing of the
system below 0.5 K.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Lattice dynamics and the electron-phonon interaction in CaRuO
We present a Raman scattering study of CaRuO, in which we investigate
the temperature-dependence of the lattice dynamics and the electron-phonon
interaction below the metal-insulator transition temperature ({\it T}). Raman spectra obtained in a backscattering geometry with light polarized
in the ab-plane reveal 9 B phonon modes (140, 215, 265, 269, 292, 388,
459, 534, and 683 cm) and 9 A phonon modes (126, 192, 204, 251, 304,
322, 356, 395, and 607 cm) for the orthorhombic crystal structure
(PbcaD). With increasing temperature toward {\it T},
the observed phonon modes shift to lower energies and exhibit reduced spectral
weights, reflecting structural changes associated with the elongation of the
RuO octahedra. Interestingly, the phonons exhibit significant increases in
linewidths and asymmetries for {\it T} {\it T}. These results
indicate that there is an increase in the effective number of electrons and the
electron-phonon interaction strengths as the temperature is raised through {\it
T}, suggesting the presence of orbital fluctuations in the
temperature regime {\it T} {\it T} {\it T}.Comment: 6 pages, 4 figure
Nuclear Magnetic Relaxation Rate in Iron-Pnictide Superconductors
Nuclear magnetic relaxation rate 1/T_1 in iron-pnictide superconductors is
calculated using the gap function obtained in a microscopic calculation. Based
on the obtained results, we discuss the issues such as the rapid decrease of
1/T_1 just below the transition temperature and the difference between nodeless
and nodal s-wave gap functions. We also investigate the effect of Coulomb
interaction on 1/T_1 in the random phase approximation and show its importance
in interpreting the experimental results.Comment: Proceedings of 9th International Conference on Materials and
Mechanisms of Superconductivity. To be published in Physica
Chandra observtaion of A2256 - a cluster at the early stage of merging
We present here \chandra observations of the rich cluster of galaxies A2256.
In addition to the known cool subcluster, a new structure was resolved 2
east of the peak of the main cluster. Its position is roughtly at the center of
a low-brightness radio halo. Spectral analysis shows that the "shoulder" has
high iron abundance ( 1). We suggest that this structure is either
another merging component or an internal structure of the main cluster. The
X-ray redshifts of several regions were measured. The results agree with the
optical ones and suggest that the main cluster, the subcluster and the
"shoulder" are physically associated and interacting. The subcluster has low
temperature ( 4.5 keV) and high iron abundance ( 0.6) in the
central 150 kpc. The \chandra image shows a relatively sharp brightness
gradient at the south of the subcluster peak running south-south-east (SSE). A
temperature jump was found across the edge, with higher temperature ahead of
the edge in the low density region. This phenomenon is qualitatively similar to
the "cold fronts" found in A2142 and A3667. If the "shoulder" is ignored, the
temperature map resembles those simulations at the early stage of merging while
the subcluster approached the main cluster from somewhere west. This fact and
the observed edge, in combination with the clear iron abundance contrast
between the center of the subcluster ( 0.6) and the main cluster (
0.2), all imply that the ongoing merger is still at the early stage. At least
three member galaxies, including a radio head-tail galaxy, were found to have
corresponding X-ray emission.Comment: The revised version. The shown abstract is shrunk. Accepted by ApJ.
If it is possible, please try to look at the high-resolution version is
http://cfa160.harvard.edu/~sunm/a2256.tar.g
Detecting the Gravitational Redshift of Cluster Gas
We examine the gravitational redshift of radiation emitted from within the
potential of a cluster. Spectral lines from the intracluster medium (ICM) are
redshifted in proportion to the emission-weighted mean potential along the line
of sight, amounting to approximately 50 km/s at a radius of 100 kpc/h, for a
cluster dispersion of 1200 km/s. We show that the relative redshifts of
different ionization states of metals in the ICM provide a unique probe of the
three-dimensional matter distribution. An examination of the reported peculiar
velocities of cD galaxies in well studied Abell clusters reveals they are
typically redshifted by an average of km/s. This can be achieved by
gravity with the addition of a steep central potential associated with the cD
galaxy. Note that in general gravitational redshifts cause a small overestimate
of the recessional velocities of clusters by an average of 20 km/s.Comment: 6 pages, 3 figures, accepted to the Astrophysical Journal Letter
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