36 research outputs found
Anisotropic magnetoresistance of spin-orbit coupled carriers scattered from polarized magnetic impurities
Anisotropic magnetoresistance (AMR) is a relativistic magnetotransport
phenomenon arising from combined effects of spin-orbit coupling and broken
symmetry of a ferromagnetically ordered state of the system. In this work we
focus on one realization of the AMR in which spin-orbit coupling enters via
specific spin-textures on the carrier Fermi surfaces and ferromagnetism via
elastic scattering of carriers from polarized magnetic impurities. We report
detailed heuristic examination, using model spin-orbit coupled systems, of the
emergence of positive AMR (maximum resistivity for magnetization along
current), negative AMR (minimum resistivity for magnetization along current),
and of the crystalline AMR (resistivity depends on the absolute orientation of
the magnetization and current vectors with respect to the crystal axes)
components. We emphasize potential qualitative differences between pure
magnetic and combined electro-magnetic impurity potentials, between short-range
and long-range impurities, and between spin-1/2 and higher spin-state carriers.
Conclusions based on our heuristic analysis are supported by exact solutions to
the integral form of the Boltzmann transport equation in archetypical
two-dimensional electron systems with Rashba and Dresselhaus spin-orbit
interactions and in the three-dimensional spherical Kohn-Littinger model. We
include comments on the relation of our microscopic calculations to standard
phenomenology of the full angular dependence of the AMR, and on the relevance
of our study to realistic, two-dimensional conduction-band carrier systems and
to anisotropic transport in the valence band of diluted magnetic
semiconductors.Comment: 15 pages, Kohn-Littinger model adde
Semiclassical framework for the calculation of transport anisotropies
We present a procedure for finding the exact solution to the linear-response
Boltzmann equation for two-dimensional anisotropic systems and demonstrate it
on examples of non-crystalline anisotropic magnetoresistance in a system with
spin-orbit interaction. We show that two decoupled integral equations must be
solved in order to find the non-equilibrium distribution function up to linear
order in the applied electric field. The examples are all based on the Rashba
system with charged magnetic scatterers, a system where the non-equilibrium
distribution function and anisotropic magnetoresistance can be evaluated
analytically. Exact results are compared to earlier widely-used approximative
approaches. We find circumstances under which approximative approaches may
become unreliable even on a qualitative level.Comment: submitted to PR
Experimental studies of generation of ~100 MeV Au-ions from the laser-produced plasma
AbstractUsing the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1ω, 3ω), on the irradiation/detection angles (0°, 30°), on the focus position with regard to the target surface, and on the target thickness (500 µm, 200 µm, 80 µm). A larger amount of the fastest ions was produced with 1ω than with 3ω, the most of the fast ions were recorded in the direction ~10°from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50 µm. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions
Self-focusing in processes of laser generation of highly-charged and high-energy heavy ions
Laser-beam interaction with expanding plasma was investigated using
the PALS high-power iodine-laser system. The interaction conditions are
significantly changing with the laser focus spot position. The decisive
role of the laser-beam self-focusing, participating in the production of
ions with the highest charge states, was proved
Angular distributions of ions emitted from laser plasma produced at various irradiation angles and laser intensities
AbstractAngular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing
Factors influencing parameters of laser ion sources
Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm
Microscopic mechanism of the noncrystalline anisotropic magnetoresistance in (Ga,Mn)As
Journals published by the American Physical Society can be found at http://journals.aps.org/Starting with a microscopic model based on the Kohn-Luttinger Hamiltonian and kinetic p-d exchange combined with Boltzmann formula for conductivity we identify the scattering from magnetic Mn combined with the strong spin-orbit interaction of the GaAs valence band as the dominant mechanism of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. This fact allows to construct a simple analytical model of the AMR consisting of two heavy-hole bands whose charge carriers are scattered on the impurity potential of the Mn atoms. The model predicts the correct sign of the AMR (resistivity parallel to magnetization is smaller than perpendicular to magnetization) and identifies its origin arising from the destructive interference between electric and magnetic part of the scattering potential of magnetic ionized Mn acceptors when the carriers move parallel to the magnetization
Efficient Electrical Spin Splitter Based on Nonrelativistic Collinear Antiferromagnetism
Electrical spin-current generation is among the core phenomena driving the
field of spintronics. Using {\em ab initio} calculations we show that a
room-temperature metallic collinear antiferromagnet RuO allows for highly
efficient spin-current generation, arising from anisotropically-split bands
with conserved up and down spins along the N\'eel vector axis. The zero net
moment antiferromagnet acts as an electrical spin-splitter with a 34
propagation angle between spin-up and spin-down currents. Correspondingly, the
spin-conductivity is a factor of three larger than the record value from a
survey of 20,000 non-magnetic spin-Hall materials. We propose a versatile
spin-splitter-torque concept utilizing antiferromagnetic RuO films
interfaced with a ferromagnet.Comment: 6 pages, 4 figure
The influence of an intense laser beam interaction with preformed plasma on the characteristics of emitted ion streams
AbstractIntense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained
Temperature-dependent resistivity and anomalous Hall effect in NiMnSb from first principles
© 2019 American Physical Society. We present implementation of the alloy analogy model within fully relativistic density-functional theory with the coherent potential approximation for a treatment of nonzero temperatures. We calculate contributions of phonons and magnetic and chemical disorder to the temperature-dependent resistivity, anomalous Hall conductivity (AHC), and spin-resolved conductivity in ferromagnetic half-Heusler NiMnSb. Our electrical transport calculations with combined scattering effects agree well with experimental literature for Ni-rich NiMnSb with 1-2% Ni impurities on Mn sublattice. The calculated AHC is dominated by the Fermi surface term in the Kubo-Bastin formula. Moreover, the AHC as a function of longitudinal conductivity consists of two linear parts in the Ni-rich alloy, while it is nonmonotonic for Mn impurities. We obtain the spin polarization of the electrical current P>90% at room temperature and we show that P may be tuned by chemical composition. The presented results demonstrate the applicability of an efficient first-principles scheme to calculate temperature dependence of linear transport coefficients in multisublattice bulk magnetic alloys