1,695 research outputs found
Disorder and interactions in quantum Hall ferromagnets near
We report on a finite-size Hartree-Fock study of the competition between
disorder and interactions in a two-dimensional electron gas near Landau level
filling factor . The ground state at evolves with increasing
disorder from a fully spin-polarized ferromagnet with a charge gap, to a
partially spin-polarized ferromagnetic Anderson insulator, to a quasi-metallic
paramagnet at the critical point between and quantum Hall plateaus.
Away from , the ground state evolves from a ferromagnetic Skyrmion
quasiparticle glass, to a conventional quasiparticle glass, and finally to a
conventional Anderson insulator. We comment on signatures of these different
regimes in low-temperature transport and NMR lineshape and peak position data.Comment: 10 pages, 8 figures, submitted to PR
Phenomenology of current-skyrmion interactions in thin films with perpendicular magnetic anisotropy
We study skyrmions in magnetic thin films with structural inversion asymmetry
perpendicular to the film plane. We determine the magnetization texture of a
single skyrmion and its dependence on the strength of the Dzyaloshinskii-Moriya
interaction relative to the magnetostatic energy. Furthermore, we construct a
phenomenological model that describes the interaction between the motion of
skyrmions and electric currents to lowest order in spin-orbit coupling. We
estimate the experimental verifiable velocities for current-driven motion of
skyrmion textures based on available results obtained from domain walls
dynamics
Boltzmann theory of engineered anisotropic magnetoresistance in (Ga,Mn)As
We report on a theoretical study of dc transport coefficients in (Ga,Mn)As
diluted magnetic semiconductor ferromagnets that accounts for quasiparticle
scattering from ionized Mn acceptors with a local moment and
from non-magnetic compensating defects. In metallic samples Boltzmann transport
theory with Golden rule scattering rates accounts for the principle trends of
the measured difference between resistances for magnetizations parallel and
perpendicular to the current. We predict that the sign and magnitude of the
anisotropic magnetoresistance can be changed by strain engineering or by
altering chemical composition.Comment: 4 pages, 2 figure
High cycle fatigue of ARMCO iron severely deformed by ECAP
The high-cycle fatigue behavior of ARMCO iron severely deformed by Equal Channel Angular Pressing (ECAP) at room temperature through route Bc until 8 passes, with an average grain size of ~365 nm, was studied and compared with the same material in the annealed state with an average grain size of ~72 µm. The fatigue limit of the 8 passes ECAPed sample increased with respect to the annealed material by more than 250% rising from 274 MPa to 717 MPa. Striations and dimpled relief were observed on the fracture surfaces of the fatigued ultrafine and coarse grain fatigue samples. The microstructure was characterized by Electron Backscattered Diffraction (EBSD) before and after the fatigue tests and it was observed in both samples an increment in the fraction of Low Angle Grain Boundaries (LAGB) at high number of cycles to failure. A texture analysis for the materials after the fatigue failure was done. This study shown a preferential orientation towards the ¿ fiber for both conditions.Peer ReviewedPostprint (author's final draft
Dielectric Function of Diluted Magnetic Semiconductors in the Infrared Regime
We present a study of the dielectric function of metallic (III,Mn)V diluted
magnetic semiconductors in the infrared regime. Our theoretical approach is
based on the kinetic exchange model for carrier induced (III,Mn)V
ferromagnetism. The dielectric function is calculated within the random phase
approximation and, within this metallic regime, we treat disorder effects
perturbatively and thermal effects within the mean field approximation. We also
discuss the implications of this calculations on carrier concentration
measurements from the optical f-sum rule and the analysis of plasmon-phonon
coupled modes in Raman spectra.Comment: 6 pages, 6 figures include
Spin-orbit torques from interfacial spin-orbit coupling for various interfaces
We use a perturbative approach to study the effects of interfacial spin-orbit
coupling in magnetic multilayers by treating the two-dimensional Rashba model
in a fully three-dimensional description of electron transport near an
interface. This formalism provides a compact analytic expression for
current-induced spin-orbit torques in terms of unperturbed scattering
coefficients, allowing computation of spin-orbit torques for various contexts,
by simply substituting scattering coefficients into the formulas. It applies to
calculations of spin-orbit torques for magnetic bilayers with bulk magnetism,
those with interface magnetism, a normal metal/ferromagnetic insulator
junction, and a topological insulator/ferromagnet junction. It predicts a
dampinglike component of spin-orbit torque that is distinct from any intrinsic
contribution or those that arise from particular spin relaxation mechanisms. We
discuss the effects of proximity-induced magnetism and insertion of an
additional layer and provide formulas for in-plane current, which is induced by
a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in
the same formalism.Comment: 24 pages, 9 figure
Large thermoelectric figure of merit for 3D topological Anderson insulators via line dislocation engineering
We study the thermoelectric properties of three-dimensional topological
Anderson insulators with line dislocations. We show that at high densities of
dislocations the thermoelectric figure of merit ZT can be dominated by
one-dimensional topologically-protected conducting states channeled through the
lattice screw dislocations in the topological insulator materials with a
non-zero time-reversal-invariant momentum such as Bi_{1-x}Sb_x. When the
chemical potential does not exceed much the mobility edge the ZT at room
temperatures can reach large values, much higher than unity for reasonable
parameters, hence making this system a strong candidate for applications in
heat management of nano-devices.Comment: 4 pages, 3 figure
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