2,602 research outputs found
Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulator Pr_{1-x}Ca_{x}MnO_{3}
The high temperature paramagnetic state in an antiferromagnetic (AFM)
insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin
fluctuations with an anomalously small energy scale. The FM fluctuations show a
precipitous decrease of the intensity at the charge ordering temperature
T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature
T_{N}. These results demonstrate the importance of the spin ordering for the
complete switching of the FM fluctuation in doped manganites.Comment: REVTeX, 5 pages, 4 figures, submitted to Phys. Rev.
Magnetization of La(2-x)Sr(x)NiO(4+ delta) (0 < x < 0.5) and observation of novel memory effects
We have studied the magnetization of a series of spin-charge ordered
La(2-x)Sr(x)NiO(4+delta) single crystals with 0 < x < 0.5. For fields applied
parallel to the ab plane there is a large irreversibility below a temperature
T(F1) ~ 50 K and a smaller irreversibility that persists up to near the charge
ordering temperature. We observed a novel memory effect in the thermo-remnant
magnetization across the entire doping range. We found that these materials
retain a memory of the temperature at which an external field was removed, and
that there is a pronounced increase in the thermo-remnant magnetization when
the system is warmed through a spin reorientation transition.Comment: 11 pages, 12 figure
Competition between hidden order and antiferromagnetism in URu_2Si_2 under uniaxial stress studied by neutron scattering
We have performed elastic neutron scattering experiments under uniaxial
stress sigma applied along the tetragonal [100], [110] and [001] directions for
the heavy electron compound URu2Si2. We found that antiferromagnetic (AF) order
with large moment is developed with sigma along the [100] and [110] directions.
If the order is assumed to be homogeneous, the staggered ordered moment mu_o
continuously increases from 0.02 mu_B (sigma=0) to 0.22 mu_B (0.25 GPa). The
rate of increase partial mu_o/partial sigma is ~ 1.0 mu_B/GPa, which is four
times larger than that for the hydrostatic pressure (partial mu_o/partial P sim
0.25 mu_B/GPa). Above 0.25 GPa, mu_o shows a tendency to saturate, similar to
the hydrostatic pressure behavior. For sigma||[001], mu_o shows only a slight
increase to 0.028 mu_B (sigma = 0.46 GPa) with a rate of ~ 0.02 mu_B/GPa,
indicating that the development of the AF state highly depends on the direction
of sigma. We have also found a clear hysteresis loop in the isothermal
mu_o(sigma) curve obtained for sigma||[110] under the zero-stress-cooled
condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is
metastable, and separated from the "hidden order" phase by a first-order phase
transition. We discuss these experimental results on the basis of crystalline
strain effects and elastic energy calculations, and show that the c/a ratio
plays a key role in the competition between these two phases.Comment: 9 pages, 7 figures, to appear in Physical Review
Incompressible viscous flow near the leading edge of a flat plate admitting slip
The shear stress at the leading edge, calculated on basis of the Navier-Stokes equations and the no-slip boundary condition, approaches infinity. However, taking into account the mean free path of the molecules, which implies admitting a certain slip, the shear stress becomes inversely proportional to the square root of the Knudsen number Îș if Îșâ0. Îș is defined as the ratio between the mean free path and the viscous length. The new boundary condition modifies the shear stress only within the Knudsen region of which the size is of the order of 3 to 4 times the mean free path.
A geometric Newton method for Oja's vector field
Newton's method for solving the matrix equation runs
up against the fact that its zeros are not isolated. This is due to a symmetry
of by the action of the orthogonal group. We show how
differential-geometric techniques can be exploited to remove this symmetry and
obtain a ``geometric'' Newton algorithm that finds the zeros of . The
geometric Newton method does not suffer from the degeneracy issue that stands
in the way of the original Newton method
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Science by, with and for citizens: rethinking âcitizen scienceâ after the 2011 Fukushima disaster
AbstractThis study illustrates how citizen-driven radiation monitoring has emerged in post-Fukushima Japan, where citizens generate their own radiation data and measurement devices to provide public with actionable data about their environments. Drawing on ethnographic fieldwork in and around Fukushima Prefecture, it highlights the multifaceted character of these bottom-up, citizen-led efforts, contrasting these initiatives with the emergence of âcitizen participatoryâ science policy discourses in Japan. Recognizing the contested nature of citizenship in Japan and in the nuclear arena, the article considers how terms and definitions shape the participation of citizens and other stakeholders (local communities, public authorities, regulators, and professional scientists) in science and technology in culturally and historically specific ways. It builds on these observations to open up new spaces of expertise, which engage all stakeholders through social-scientific intervention.</jats:p
Microwave properties of Nd_0.5Sr_0.5MnO_3: a key role of the (x^2-y^2)-orbital effects
Transmittance of the colossal magnetoresistive compound Nd_0.5Sr_0.5MnO_3
showing metal-insulator phase transition has been studied by means of the
submm- and mm-wavelength band spectroscopy. An unusually high transparency of
the material provided direct evidence for the significant suppression of the
coherent Drude weight in the ferromagnetic metallic state. Melting of the
A-type antiferromagnetic states has been found to be responsible for a
considerable increase in the microwave transmission, which was observed at the
transition from the insulating to the metallic phase induced by magnetic field
or temperature. This investigation confirmed a dominant role of the
(x^2-y^2)-orbital degree of freedom in the low-energy optical properties of
Nd_0.5Sr_0.5MnO_3 and other doped manganites with planar (x^2-y^2)-orbital
order, as predicted theoretically. The results are discussed in terms of the
orbital-liquid concept.Comment: 8 pages, 3 figure
Effect of interchain separation on the photoinduced absorption spectra of polycarbazolyldiacetylenes
The photoinduced absorption spectra of a novel polycarbazolyldiacetylene with long aliphatic chains on the carbazolyl side groups are measured and compared with those of the unsubstituted polyDCHD. The two polymers in the blue form exhibit very similar electronic absorption spectra and Raman frequencies. This fact indicates that the conjugation length of the polydiacetylene backbone is not too affected by the long substituents. In contrast, the near steady-state photoinduced absorption spectra show that different photogeneration mechanisms are involved in the two polymers. This result can be ascribed to the role played by the interchain distance in the dynamics of the relaxation processes in polydiacetylenes
Stripe order at low temperatures in La{2-x}Sr{x}NiO4 for 1/3 < x < 1/2
Stripe order in La{2-x}Sr{x}NiO4 beyond x = 1/3 was studied with neutron
scattering technique. At low temperatures, all the samples exhibit hole stripe
order. Incommensurability \epsilon of the stripe order is approximately linear
in the hole concentration n_h = x + 2\delta up to x = 1/2, where \delta denotes
the off-stoichiometry of oxygen atoms. The charge and spin ordering
temperatures exhibit maxima at n_h = 1/3, and both decrease beyond n_h > 1/3.
For 1/3 < n_h < 1/2, the stripe ordering consists of the mixture of the
\epsilon = 1/3 stripe order and the n_h = 1/2 charge/spin order.Comment: REVTeX, 4 pages, 4 figure
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