Search results for "electrons"
showing 10 items of 1325 documents
Small-polaron transport inLa0.67Ca0.33MnO3thin films
1998
We present a detailed study of the activated resistivity of ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}$ films up to 600 K under the influence of high magnetic fields. Data in zero field can be explained by small polaron hopping as treated in the Friedman-Holstein theory. Based on the spin orientation of ferromagnetic clusters in a magnetic field, we develop a phenomenological model describing the temperature and field dependence of the resistivity with a minimum of free parameters. We find that the polarons have a magnetic contribution to their activation energy for hopping which depends on the variation of the spin order with increasing temperature and can be modified by a…
Discovery of a Transition to Global Spin-up in EXO 2030+375
2005
EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion, has been observed to undergo an outburst at nearly every periastron passage for the last 13.5 years. From 1994 through 2002, the global trend in the pulsar spin frequency was spin-down. Using RXTE data from 2003 September, we have observed a transition to global spin-up in EXO 2030+375. Although the spin frequency observations are sparse, the relative spin-up between 2002 June and 2003 September observations, along with an overall brightening of the outbursts since mid 2002 observed with the RXTE ASM, accompanied by an increase in density of the Be disk, indicated by infrared magnitudes, suggest that the pattern obse…
Theoretical study of resonant x-ray emission spectroscopy of Mn films on Ag.
2006
We report a theoretical study on resonant x-ray emission spectra (RXES) in the whole energy region of the Mn $L_{2,3}$ white lines for three prototypical Mn/Ag(001) systems: (i) a Mn impurity in Ag, (ii) an adsorbed Mn monolayer on Ag, and (iii) a thick Mn film. The calculated RXES spectra depend strongly on the excitation energy. At $L_3$ excitation, the spectra of all three systems are dominated by the elastic peak. For excitation energies around $L_2$, and between $L_3$ and $L_2$, however, most of the spectral weight comes from inelastic x-ray scattering. The line shape of these inelastic ``satellite'' structures changes considerably between the three considered Mn/Ag systems, a fact tha…
Thermal disorder driven magnetic phases in van der Waals magnet CrI3
2020
Abstract Magnetic phase transitions often occur spontaneously at specific critical temperatures and are instrumental to understand the origin of long-range spin order in condensed matter systems. The presence of more than one critical temperature (Tc) has been observed in several compounds where the coexistence of competing magnetic orders highlights the importance of phase separation driven by different factors such as pressure, temperature and chemical composition. However, it is unknown whether recently discovered two-dimensional (2D) van der Walls (vdW) magnetic materials show such intriguing phenomena that can result in rich phase diagrams with novel magnetic features to be explored. H…
Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors
2001
We suggest an approach to account for spatial (composition) and thermal fluctuations in "disordered" magnetic models (e.g. Heisenberg, Ising) with given spatial dependence of magnetic spin-spin interaction. Our approach is based on introduction of fluctuating molecular field (rather than mean field) acting between the spins. The distribution function of the above field is derived self-consistently. In general case this function is not Gaussian, latter asymptotics occurs only at sufficiently large spins (magnetic ions) concentrations $n_i$. Our approach permits to derive the equation for a critical temperature $T_c$ of ferromagnetic phase transition with respect to the above fluctuations. We…
Orbital dimerization in NaTiSi2O6: An orbital analogue of the spin-Peierls phase transition
2004
We measure the Raman scattering spectra of NaTiSi2O6, analyze the vibrational properties, and study the origin of the phase transition in this compound. In this quasi-one-dimensional S = 1/2 system we observe anomalous high-temperature phonon broadenings, and large changes of the phonon energies and line-widths across the phase transition temperature of 210 K. These results, combined with theoretical considerations, indicate that the phonon anomalies originate from an orbital order-disorder type of phase transition. We find that the high temperature dynamical Jahn-Teller phase of NaTiSi2O6 exhibits a spontaneous breaking of translational symmetry into a dimerized, Jahn-Teller distorted, orb…
Statistical properties of the eigenvalue spectrum of the three-dimensional Anderson Hamiltonian
1993
A method to describe the metal-insulator transition (MIT) in disordered systems is presented. For this purpose the statistical properties of the eigenvalue spectrum of the Anderson Hamiltonian are considered. As the MIT corresponds to the transition between chaotic and nonchaotic behavior, it can be expected that the random matrix theory enables a qualitative description of the phase transition. We show that it is possible to determine the critical disorder in this way. In the thermodynamic limit the critical point behavior separates two different regimes: one for the metallic side and one for the insulating side.
Relation between Energy Level Statistics and Phase Transition and its Application to the Anderson Model
1994
A general method to describe a second-order phase transition is discussed. It starts from the energy level statistics and uses of finite-size scaling. It is applied to the metal-insulator transition (MIT) in the Anderson model of localization, evaluating the cumulative level-spacing distribution as well as the Dyson-Metha statistics. The critical disorder $W_{c}=16.5$ and the critical exponent $\nu=1.34$ are computed.
Anisotropic exchange in ErSb
1983
The correlations of the magnetic moments and the magnetic order parameter of ErSb have been studied by neutron diffraction. The antiferromagnetic phase transition is of first order. The diffuse paramagnetic scattering is evaluated in terms of magnetic coupling tensors which are characterized by a strong two-ion anisotropy.
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
2008
4 páginas, 5 figuras.-- PACS numbers: 78.67.Lt, 71.30.+h, 71.35. -y.-- Comunicación presentada a la International Conference on the Physics of Semiconductors (ICPS) celebrada en Rio de Jqaneiro (Brasil/2008).