56 research outputs found
Dynamical Corrections to Spin Wave Excitations in Quantum Wells due to Coulomb Interactions and Magnetic Ions
We have measured dispersions of spin-flip waves and spin-flip single-particle
excitations of a spin polarized two-dimensional electron gas in a CdMnTe
quantum well using resonant Raman scattering. We find the energy of the
spin-flip wave to be below the spin-flip single particle excitation continuum,
a contradiction to the theory of spin waves in diluted magnetic semiconductors
put forth in [Phys. Rev. B 70, 045205 (2004)]. We show that the inclusion of
terms accounting for the Coulomb interaction between carriers in the spin wave
propagator leads to an agreement with our experimental results. The dominant
Coulomb contribution leads to an overall red shift of the mixed electron-Mn
spin modes while the dynamical coupling between Mn ions results in a small blue
shift. We provide a simulated model system which shows the reverse situation
but at an extremely large magnetic field.Comment: 6 pages, 7 figure
Coulomb-driven organization and enhancement of spin-orbit fields in collective spin excitations
Spin-orbit (SO) fields in a spin-polarized electron gas are studied by
angle-resolved inelastic light scattering on a CdMnTe quantum well. We
demonstrate a striking organization and enhancement of SO fields acting on the
collective spin excitation (spin-flip wave). While individual electronic SO
fields have a broadly distributed momentum dependence, giving rise to
D'yakonov-Perel' dephasing, the collective spin dynamics is governed by a
single collective SO field which is drastically enhanced due to many-body
effects. The enhancement factor is experimentally determined. These results
provide a powerful indication that these constructive phenomena are universal
to collective spin excitations of conducting systems.Comment: 5 pages, 4 figure
Magnetization dynamics down to zero field in dilute (Cd,Mn)Te quantum wells
The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short
pulse of magnetic field was determined from the giant Zeeman shift of
spectroscopic lines. The dynamics in absence of magnetic field was found to be
up to three orders of magnitude faster than that at 1 T. Hyperfine interaction
and strain are mainly responsible for the fast decay. The influence of a hole
gas is clearly visible: at zero field anisotropic holes stabilize the system of
Mn ions, while in a magnetic field of 1 T they are known to speed up the decay
by opening an additional relaxation channel
Advanced Image Analysis of the Surface Pattern Emerging in Ni3Al Intermetallic Alloys on Anodization
Anodization of Ni3Al alloy is of interest in the field of industrial manufacturing, thanks to the formation of protective oxide layer on the materials working in corrosive environments and high temperatures. However, homogeneous surface treatment is paramount for technological applications of this material. The anodization conditions have to be set outside the ranges of corrosion and burning, which is the electric field enhanced anodic dissolution of the metal. In order to check against occurrence of these events, proper quantitative means for assessing the surface quality have to be developed and established. We approached this task by advanced analysis of scanning electron microscope images of anodized Ni3Al plates. The anodization was carried out in 0.3 M citric acid at two temperatures of 0 and 30°C and at voltages in the range of 2 12 V. Different figures can be used to characterize the quality of the surface, in terms of uniformity. Here, the concept of regularity ratio spread is used for the first time on surfaces of technological interest. Additionally, the Minkowski parameters have been calculated and their meaning is discussed
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