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Free electron model
About: Free electron model is a research topic. Over the lifetime, 4678 publications have been published within this topic receiving 103535 citations.
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TL;DR: In this paper, the spin wave spectra obtained from thin films of the iron group metals are discussed, mainly with reference to the spectrum of iron, and it is found that specimens can be manufactured whose resonance absorption modes are very similar to those predicted by the simple model of spin wave resonance.
Abstract: The spin wave spectra obtained from thin films of the iron group metals are discussed, mainly with reference to the spectrum of iron. It is found that, under suitable growth conditions, specimens can be manufactured whose resonance absorption modes are very similar to those predicted by the simple model of spin wave resonance. Three iron films are examined whose thicknesses range from 1800 to 4200 $\overset{\circ}{\mathrm A}$ and all give similar values for the spin wave coupling constant D. The constant D is examined as a function of temperature and is found to behave in a similar way to nickel and cubic cobalt, giving a 10% variation of D between 20 and 300 $^\circ$K. A logarithmic plot indicates that a T$^\frac{3}{2}$ law is obeyed for most of the temperature range, but it is also possible to fit the points to a T$^2$ plot, in accord with the itinerant electron model, provided other power law terms are assumed present. These other terms might be the spin wave interaction T$^\frac{5}{2}$ term or that due to the effect of thermal expansion. The linewidths observed in the iron resonances are discussed, and reasons based on the ineffectiveness of the two magnon scattering processes are put forward for these narrow lines ($\sim$ 37 Oe) as opposed to the much broader lines often found in ferromagnetic resonance.
32 citations
TL;DR: In this article, it was shown that the critical nearest-neighbor Coulomb interaction is different for each spin subspace, with the critical value decreasing with increasing spin, and that with the lowering of temperature, there can occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls state that is a bond-charge-density wave with charge occupancies different from the WIGNer crystal.
Abstract: It is known that within the interacting electron model Hamiltonian for the one-dimensional $\frac{1}{4}$-filled band, the singlet ground state is a Wigner crystal only if the nearest-neighbor electron-electron repulsion is larger than a critical value. We show that this critical nearest-neighbor Coulomb interaction is different for each spin subspace, with the critical value decreasing with increasing spin. As a consequence, with the lowering of temperature, there can occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls state that is a bond-charge-density wave with charge occupancies different from the Wigner crystal. This transition is possible because spin excitations from the spin-Peierls state in the $\frac{1}{4}$-filled band are necessarily accompanied by changes in site charge densities. We apply our theory to the $\frac{1}{4}$-filled band quasi-one-dimensional organic charge-transfer solids, in general, and to 2:1 tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenafulvalene cationic salts, in particular. We believe that many recent experiments strongly indicate the Wigner crystal to bond-charge-density Wave transition in several members of the TMTTF family. We explain the occurrence of two different antiferromagnetic phases but a single spin-Peierls state in the generic phase diagram for the 2:1 cationic solids. The antiferromagnetic phases can have either the Wigner crystal or the bond-charge-spin-density wave charge occupancies. The spin-Peierls state is always a bond-charge-density wave.
32 citations
TL;DR: In this article, free-electron optical absorption of Se-doped GaAs at room temperature is calculated and compared with existing experimental data, taking into account a non-parabolic character of the conduction band, a short-range component of the Se donor potential and a plasmon generation in the presence of donors.
32 citations
TL;DR: An experiment in which the attenuation of a spin-polarized free electron beam is measured by direct transmission through an ultrathin ferromagnetic layer and it is found that the transmission coefficient of minority spin electrons is about 0.7 times that of majority spin electrons.
Abstract: We present an experiment in which the attenuation of a spin-polarized free electron beam is measured by direct transmission through an ultrathin ferromagnetic layer. The self-supported metal target consists of a 1-nm-thick cobalt film sandwiched between 21- and 2-nm-thick gold layers. Measurements are performed throughout a wide energy range (incident electron energies from 4 eV to 50 eV above the Fermi level). At low energy, close to the clean surface vacuum level, we find that the transmission coefficient of minority spin electrons is about 0.7 times that of majority spin electrons.
31 citations
01 May 2000-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the authors demonstrated and measured the super-radiant emission in a wide band of frequencies from 3.15 to 5.5 GHz using the mini-FEM of Tel-Aviv University, wherein pre-bunching at the radiation frequency is accomplished with the aid of a traveling-wave prebuncher.
Abstract: It is well known that electrons passing through a magnetic undulator emit partially coherent radiation: “Undulator Synchrotron Radiation”. Radiation from electrons, entering the undulator at random, adds incoherently. If the electron beam is periodically modulated (bunched) to pulses shorter than the radiation wavelength, electrons radiate in phase with each other, resulting in super-radiant emission at the bunching frequency. Introduction of a signal at the input of the prebunched beam FEL, results in stimulated super-radiant emission. The interaction between the electromagnetic wave and a synchronous modulated e-beam results in amplification of the signal wave in addition to the spontaneous super-radiant emission. We demonstrated and measured the super-radiant emission in a wide band of frequencies from 3.15 to 5.5 GHz using the mini-FEM of Tel-Aviv University, wherein pre-bunching at the radiation frequency is accomplished with the aid of a traveling-wave prebuncher. The measured upper synchronous frequency is centered about 4.5 GHz and the lower synchronous frequency is just above cutoff (near 3.153 GHz). Analytical models, computer simulations and experimental results of a pre-bunched free-electron laser operation are presented and compared. The power levels that can be achieved are discussed. The measured results agree well with results predicted theoretically and obtained by a 3D simulation code.
31 citations