104 research outputs found
Pressure-induced polarization reversal in multiferroic
The low-temperature ferroelectric polarization of multiferroic is
completely reversed at a critical pressure of 10 kbar and the phase transition
from the incommensurate to the commensurate magnetic phase is induced by
pressures above 14 kbar. The high-pressure data correlate with thermal
expansion measurements indicating a significant lattice strain at the
low-temperature transition into the incommensurate phase. The results support
the exchange striction model for the ferroelectricity in multiferroic
compounds and they show the importance of magnetic frustration as
well as the spin-lattice coupling
Multiferroicity in doped hexagonal LuFeO3
The hexagonal phase of LuFeO3 is a rare example of a multiferroic material possessing a weak ferromagnetic moment, which is predicted to be switchable by an electric field. We stabilize this structure in bulk form though Mn and Sc doping, and determine the complete magnetic and crystallographic structures using neutron-scattering and magnetometry techniques. The ferroelectric P6(3)cm space group is found to be stable over a wide concentration range, ordering antiferromagnetically with Neel temperatures that smoothly increase following the ratio of c to a (c/a) lattice parameters up to 172 K, the highest found in this class of materials to date. The magnetic structure for a range of temperatures and dopings is consistent with recent studies of high quality epitaxial films of pure hexagonal LuFeO3 including a ferromagnetic moment parallel to the ferroelectric axis. We propose a mechanism by which room-temperature multiferroicity could be achieved in this class of materialsopen
Vibronic coupling and band gap trends in CuGeO3 nanorods
We measured the optical response of CuGeO3 nanorods in order to reveal size effects on the electronic properties. The vibronically activated d-to-d color band excitations are activated by the 131 and 478 cm−1 phonons, with the relative contribution of the lower frequency O-Cu-O bending mode increasing with decreasing size until it dominates the process. We also uncover trends in the direct band gap, with the charge transfer edge hardening with decreasing size. These findings advance the understanding of size effects in low-dimensional copper oxides
Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn2O5
Comparative studies of magnetoelectric susceptibility (??), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the ??(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested.open3
Observation of two time scales in the ferromagnetic manganite La(1-x)Ca(x)MnO(3), x = 0.3
We report new zero-field muon spin relaxation and neutron spin echo
measurements in ferromagnetic (FM) (La,Ca)MnO3 which taken together suggest two
spatially separated regions in close proximity possessing very different Mn-ion
spin dynamics. One region corresponds to an extended cluster which displays
'critical slowing down' near Tc and an increasing volume fraction below Tc. The
second region possesses more slowly fluctuating spins and a decreasing volume
fraction below Tc. These data are discussed in terms of the growth of small
polarons into overlapping regions of correlated spins below Tc, resulting in a
microscopically inhomogeneous FM transition.Comment: 10 pages, 3 figure
Observation of a multiferroic critical end point
The study of abrupt increases in magnetization with magnetic field known as
metamagnetic transitions has opened a rich vein of new physics in itinerant
electron systems, including the discovery of quantum critical end points with a
marked propensity to develop new kinds of order. However, the electric analogue
of the metamagnetic critical end point, a "metaelectric" critical end point has
not yet been realized. Multiferroic materials wherein magnetism and
ferroelectricity are cross-coupled are ideal candidates for the exploration of
this novel possibility using magnetic-field (\emph{H}) as a tuning parameter.
Herein, we report the discovery of a magnetic-field-induced metaelectric
transition in multiferroic BiMnO in which the electric polarization
(\emph{P}) switches polarity along with a concomitant Mn spin-flop transition
at a critical magnetic field \emph{H}. The simultaneous metaelectric
and spin-flop transitions become sharper upon cooling, but remain a continuous
crossover even down to 0.5 K. Near the \emph{P}=0 line realized at
\emph{H}18 T below 20 K, the dielectric constant
() increases significantly over wide field- and temperature
(\emph{T})-ranges. Furthermore, a characteristic power-law behavior is found in
the \emph{P}(\emph{H}) and (\emph{H}) curves at \emph{T}=0.66 K.
These findings indicate that a magnetic-field-induced metaelectric critical end
point is realized in BiMnO near zero temperature.Comment: 6 pages, 3 figure
Sex- and age-dependent association of SLC11A1 polymorphisms with tuberculosis in Chinese: a case control study
BACKGROUND: Host genetic factors are important determinants in tuberculosis (TB). The SLC11A1 (or NRAMP1) gene has been studied extensively for genetic association with TB, but with inconsistent findings. In addition, no study has yet looked into the effect of sex and age on the relationship between SLC11A1 polymorphisms and TB. METHODS: A case-control study was conducted. In total, 278 pulmonary TB patients and 282 sex- and age-matched controls without TB were recruited. All subjects were ethnic Chinese. On the basis of linkage disequilibrium pattern, three genetic markers from SLC11A1 and one from the nearby IL8RB locus were selected and examined for association with TB susceptibility. These markers were genotyped using single strand conformation polymorphism analysis or fragment analysis of amplified products. RESULTS: Statistically significant differences in allele (P = 0.0165, OR = 1.51) and genotype (P = 0.0163, OR = 1.59) frequencies of the linked markers SLC6a/b (classically called D543N and 3'UTR) of the SLC11A1 locus were found between patients and controls. With stratification by sex, positive associations were identified in the female group for both allele (P = 0.0049, OR = 2.54) and genotype (P = 0.0075, OR = 2.74) frequencies. With stratification by age, positive associations were demonstrated in the young age group (age ≤65 years) for both allele (P = 0.0047, OR = 2.52) and genotype (P = 0.0031, OR = 2.92) frequencies. All positive findings remained significant even after correction for multiple comparisons. No significant differences were noted in either the male group or the older age group. No significant differences were found for the other markers (one SLC11A1 marker and one IL8RB marker) either. CONCLUSION: This study confirmed the association between SLC11A1 and TB susceptibility and demonstrated for the first time that the association was restricted to females and the young age group
Magnetic Field Properties inside the Jet of Mrk 421: Multiwavelength Polarimetry Including the Imaging X-ray Polarimetry Explorer
We conducted a polarimetry campaign from radio to X-ray wavelengths of the
high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry
Explorer (IXPE) measurements on 2022 December 6-8. We detected X-ray
polarization of Mrk 421 with a degree of =141 and an
electric-vector position angle =1073 in the 2-8
keV band. From the time variability analysis, we find a significant episodic
variation in . During 7 months from the first IXPE pointing of
Mrk 421 in 2022 May, varied across the range of 0 to
180, while maintained similar values within
10-15. Furthermore, a swing in in 2022 June was
accompanied by simultaneous spectral variations. The results of the
multiwavelength polarimetry show that the X-ray polarization degree was
generally 2-3 times greater than that at longer wavelengths, while the
polarization angle fluctuated. Additionally, based on radio, infrared, and
optical polarimetry, we find that rotation of occurred in the opposite
direction with respect to the rotation of over longer timescales
at similar epochs. The polarization behavior observed across multiple
wavelengths is consistent with previous IXPE findings for HSP blazars. This
result favors the energy-stratified shock model developed to explain variable
emission in relativistic jets. The accompanying spectral variation during the
rotation can be explained by a fluctuation in the physical
conditions, e.g., in the energy distribution of relativistic electrons. The
opposite rotation direction of between the X-ray and longer-wavelength
polarization accentuates the conclusion that the X-ray emitting region is
spatially separated from that at longer wavelengths.Comment: 17 pages, 13 figures, 4 tables; Accepted for publication in A&
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