699 research outputs found
Controlled switching of intrinsic localized modes in a 1-D antiferromagnet
Nearly steady-state locked intrinsic localized modes (ILMs) in the quasi-1d
antiferromagnet (C2H5NH3)2CuCl4 are detected via four-wave mixing emission or
the uniform mode absorption. Exploiting the long-time stability of these locked
ILMs, repeatable nonlinear switching is observed by varying the sample
temperature, and localized modes with various amplitudes are created by
modulation of the microwave driver power. This steady-state ILM locking
technique could be used to produce energy localization in other atomic
lattices.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett. v.2 :
clarifications of text and figures in response to comment
Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature
The field-driven reorientation transition of an anisotropic ferromagnetic
monolayer is studied within the context of a finite-temperature Green's
function theory. The equilibrium state and the field dependence of the magnon
energy gap are calculated for static magnetic field applied in plane
along an easy or a hard axis. In the latter case, the in-plane reorientation of
the magnetization is shown to be continuous at T=0, in agreement with free spin
wave theory, and discontinuous at finite temperature , in contrast with
the prediction of mean field theory. The discontinuity in the orientation angle
creates a jump in the magnon energy gap, and it is the reason why, for ,
the energy does not go to zero at the reorientation field. Above the Curie
temperature , the magnon energy gap vanishes for H=0 both in the
easy and in the hard case. As is increased, the gap is found to increase
almost linearly with , but with different slopes depending on the field
orientation. In particular, the slope is smaller when is along the hard
axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist
well above ().Comment: Final version accepted for publication in Physical Review B (with
three figures
Electron paramagnetic resonance studies of the insulating ferromagnetic manganite Nd_0.8Pb_0.2MnO_3 above the transition temperature
Single crystals of Nd_{1-x}Pb_{x}MnO_{3} with x=0.2 are grown by high
temperature solution growth technique using PbO-PbF_{2} flux. Magnetization
studies on the samples show a transition to a ferromagnetic state below T_c ~
125 K and the resistivity measurements show it to be an insulator throughout
the temperature range 50 - 300 K. Electron Paramagnetic Resonance studies have
been performed for T > T_{C} with a view to comparing the results with those on
metallic ferromagnetic manganites. The temperature dependence of various
parameters like g-value, linewidth and intensity has been studied in the
temperature range 150 - 300 K. It is found that they behave in a manner similar
to that exhibited by metallic ferromagnetic manganites.Comment: 8 pages, 4 figure
Four-terminal resistance of an interacting quantum wire with weakly invasive contacts
We analyze the behavior of the four-terminal resistance, relative to the
two-terminal resistance of an interacting quantum wire with an impurity, taking
into account the invasiveness of the voltage probes. We consider a
one-dimensional Luttinger model of spinless fermions for the wire. We treat the
coupling to the voltage probes perturbatively, within the framework of
non-equilibrium Green function techniques. Our investigation unveils the
combined effect of impurities, electron-electron interactions and invasiveness
of the probes on the possible occurrence of negative resistance.Comment: 10 pages, 7 figure
Discourse and identity in a corpus of lesbian erotica
This article uses corpus linguistic methodologies to explore representations of lesbian desires and identities in a corpus of lesbian erotica from the 1980s and 1990s. We provide a critical examination of the ways in which “lesbian gender,” power, and desire are represented, (re-)produced, and enacted, often in ways that challenge hegemonic discourses of gender and sexuality. By examining word frequencies and collocations, we critically analyze some of the themes, processes, and patterns of representation in the texts. Although rooted in linguistics, we hope this article provides an accessible, interdisciplinary, and timely contribution toward developing understandings of discursive practices surrounding gender and sexuality
Evidence for magnetic clusters in BaCoO
Magnetic properties of the transition metal oxide BaCoO are analyzed on
the basis of the experimental and theoretical literature available via ab inito
calculations. These can be explained by assuming the material to be formed by
noninteracting ferromagnetic clusters of about 1.2 nm in diameter separated by
about 3 diameters. Above about 50 K, the so-called blocking temperature,
superparamagnetic behavior of the magnetic clusters occurs and, above 250 K,
paramagnetism sets in.Comment: 4 pages, 1 figur
First principles study of the multiferroics BiFeO, BiFeCrO, and BiCrO: Structure, polarization, and magnetic ordering temperature
We present results of an {\it ab initio} density functional theory study of
three bismuth-based multiferroics, BiFeO, BiFeCrO, and
BiCrO. We disuss differences in the crystal and electronic structure of
the three systems, and we show that the application of the LDA+ method is
essential to obtain realistic structural parameters for BiFeCrO. We
calculate the magnetic nearest neighbor coupling constants for all three
systems and show how Anderson's theory of superexchange can be applied to
explain the signs and relative magnitudes of these coupling constants. From the
coupling constants we then obtain a mean-field approximation for the magnetic
ordering temperatures. Guided by our comparison of these three systems, we
discuss the possibilities for designing a multiferroic material with large
magnetization above room temperature.Comment: 8 Pages, 4 Figure
Thermal Casimir Force between Magnetic Materials
We investigate the Casimir pressure between two parallel plates made of
magnetic materials at nonzero temperature. It is shown that for real
magnetodielectric materials only the magnetic properties of ferromagnets can
influence the Casimir pressure. This influence is accomplished through the
contribution of the zero-frequency term of the Lifshitz formula. The
possibility of the Casimir repulsion through the vacuum gap is analyzed
depending on the model used for the description of the dielectric properties of
the metal plates.Comment: 9 pages, 3 figures. Contribution to the Proceedings of QFEXT09,
Norman, OK, September 21-25, 200
Magnetization Dynamics, Gyromagnetic Relation, and Inertial Effects
The gyromagnetic relation - i.e. the proportionality between the angular
momentum (defined by an inertial tensor) and the magnetization - is evidence of the intimate connections between the magnetic properties
and the inertial properties of ferromagnetic bodies. However, inertia is absent
from the dynamics of a magnetic dipole (the Landau-Lifshitz equation, the
Gilbert equation and the Bloch equation contain only the first derivative of
the magnetization with respect to time). In order to investigate this
paradoxical situation, the lagrangian approach (proposed originally by T. H.
Gilbert) is revisited keeping an arbitrary nonzero inertial tensor. A dynamic
equation generalized to the inertial regime is obtained. It is shown how both
the usual gyromagnetic relation and the well-known Landau-Lifshitz-Gilbert
equation are recovered at the kinetic limit, i.e. for time scales above the
relaxation time of the angular momentum.Comment: 10 pages, 1 figur
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