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 $T_2$. 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

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

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 ${\bf k}$-space.Comment: 13 pages, 4 figures, submitted to Phys Rev

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

Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system

We report on the magnetic excitation spectrum of the coupled spin tetrahedral system Cu$_{2}$Te$_{2}$O$_{5}$Cl$_{2}$ using Raman scattering on single crystals. The transition to an ordered state at T$_{N}^{Cl}$=18.2 K evidenced from thermodynamic data leads to the evolution of distinct low-energy magnetic excitations superimposed by a broad maximum. These modes are ascribed to magnons with different degree of localization and a two-magnon continuum. Two of the modes develop a substantial energy shift with decreasing temperature similar to the order parameter of other Neel ordered systems. The other two modes show only a negligible temperature dependence and dissolve above the ordering temperature in a continuum of excitations at finite energies. These observations point to a delicate interplay of magnetic inter- and intra-tetrahedra degrees of freedom and an importance of singlet fluctuations in describing a spin dynamics.Comment: 7pages, 6figures, 1tabl