918 research outputs found
Nonlinear Dynamics of Nuclear-Electronic Spin Processes in Ferromagnets
Spin dynamics is considered in ferromagnets consisting of electron and
nuclear subsystems interacting with each other through hyperfine forces. In
addition, the ferromagnetic sample is coupled with a resonance electric
circuit. Under these conditions, spin relaxation from a strongly nonequilibrium
initial state displays several peculiarities absent for the standard set-up in
studying spin relaxation. The main feature of the nonlinear spin dynamics
considered in this communication is the appearance of ultrafast coherent
relaxation, with characteristic relaxation times several orders shorter than
the transverse relaxation time . This type of coherent spin relaxation can
be used for extracting additional information on the intrinsic properties of
ferromagnetic materials and also can be employed for different technical
applications.Comment: 1 file, 4 pages, RevTex, no figure
Detection of X-ray line emission from the shell of SNR B0540-69.3 with XMM-Newton RGS
We present X-ray observations of PSR 0540-69.3 with the XMM-Newton
observatory. The spectra obtained with the Reflection Grating Spectrometer
reveal, for the first time, emission from ionized species of O, Ne and Fe
originating from the SNR shell. Analysis of the emission line spectrum allows
us to derive estimates of the temperature, ionization timescale, abundances,
location, and velocity of the emitting gas.Comment: 5 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics, letters (XMM issue
One-magnon Raman scattering in La(2)CuO(4): the origin of the field-induced mode
We investigate the one-magnon Raman scattering in the layered
antiferromagnetic La(2)CuO(4) compound. We find that the Raman signal is
composed by two one-magnon peaks: one in the B1g channel, corresponding to the
Dzyaloshinskii-Moryia (DM) mode, and another in the B3g channel, corresponding
to the XY mode. Furthermore, we show that a peak corresponding to the XY mode
can be induced in the planar (RR) geometry when a magnetic field is applied
along the easy axis for the sublattice magnetization. The appearance of such
field-induced mode (FIM) signals the existence of a new magnetic state above
the Neel temperature T_N, where the direction of the weak-ferromagnetic moment
(WFM) lies within the CuO(2) planes.Comment: 4 pages, 3 figure
Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling
Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.Comment: 1 file, LaTex, 23 page
Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves
We describe a simple method of including dissipation in the spin wave band
structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz
equation for the magnetization with the Gilbert damping term. We use this
approach to calculate the band structure of square and triangular arrays of Ni
nanocylinders embedded in an Fe host. The results show that there are certain
bands and special directions in the Brillouin zone where the spin wave lifetime
is increased by more than an order of magnitude above its average value. Thus,
it may be possible to generate spin waves in such composites decay especially
slowly, and propagate especially large distances, for certain frequencies and
directions in -space.Comment: 13 pages, 4 figures, submitted to Phys Rev
The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation
Gravitationally redshifted absorption lines from highly ionized iron have
been previously identified in the burst spectra of the neutron star in EXO
0748-676. To repeat this detection we obtained a long, nearly 600 ks
observation of the source with XMM-Newton in 2003. The spectral features seen
in the burst spectra from the initial data are not reproduced in the burst
spectra from this new data. In this paper we present the spectra from the 2003
observations and discuss the sensitivity of the absorption structure to changes
in the photospheric conditions.Comment: 18 Pages, 3 Figures. Accepted for publication in Ap
Intrinsic Energy Localization through Discrete Gap Breathers in One-Dimensional Diatomic Granular Crystals
We present a systematic study of the existence and stability of discrete
breathers that are spatially localized in the bulk of a one-dimensional chain
of compressed elastic beads that interact via Hertzian contact. The chain is
diatomic, consisting of a periodic arrangement of heavy and light spherical
particles. We examine two families of discrete gap breathers: (1) an unstable
discrete gap breather that is centered on a heavy particle and characterized by
a symmetric spatial energy profile and (2) a potentially stable discrete gap
breather that is centered on a light particle and is characterized by an
asymmetric spatial energy profile. We investigate their existence, structure,
and stability throughout the band gap of the linear spectrum and classify them
into four regimes: a regime near the lower optical band edge of the linear
spectrum, a moderately discrete regime, a strongly discrete regime that lies
deep within the band gap of the linearized version of the system, and a regime
near the upper acoustic band edge. We contrast discrete breathers in anharmonic
FPU-type diatomic chains with those in diatomic granular crystals, which have a
tensionless interaction potential between adjacent particles, and highlight in
that the asymmetric nature of the latter interaction potential may lead to a
form of hybrid bulk-surface localized solutions
Reprogrammable magnonic band structure of layered Permalloy/Cu/Permalloy nanowires
Reprogrammability of magnonic band structure in layered
Permalloy/Cu/Permalloy nanowires is demonstrated to depend on the relative
orientation of the two layers magnetization. By using Brillouin light
spectroscopy, we show that when the layers are aligned parallel two dispersive
modes, with positive and negative group velocity, are observed while when the
magnetic layers are aligned anti-parallel, only one dispersive mode, with
positive group velocity, is detected. Our findings are successfully compared
and interpreted in terms of a microscopic (Hamiltonian-based) method. An
explanation for the observed behavior can be attributed to mode-mixing (or
hybridization) effect when the two magnetic layers are aligned anti-parallel.
This work opens the path to magnetic field-controlled reconfigurable magnonic
crystals with multi-modal frequency transmission characteristics
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