Search results for "Hall effect"

Spin transport in ferromagnetic/normal-metal tunnel junction arrays

2012

Published version of an article in the journal: Physical Review B. Also available from the publisher:http://dx.doi.org/10.1103/PhysRevB.85.094421 An array of alternating ferromagnetic and normal-metal islands separated by small tunnel junctions is theoretically investigated in the sequential tunneling regime. A numerical Monte Carlo method is used to calculate the transport properties. The spin-dependent tunneling currents give rise to nonequilibrium spin accumulation on the normal island. The tunneling magneto resistance (TMR) is calculated for a large range of array parameters. The TMR oscillates with bias voltage and can become negative for certain array parameters. We show that the long…

Competition between carrier recombination and tunneling in quantum dots and rings under the action of electric fields

2008

6 páginas, 3 figuras.-- Proceedings of the 7th International Conference on Physics of Light-Matter Coupling in Nanostructures.

Evidence of charge-carrier compensation effects inLa0.67Ca0.33MnO3

1998

We report on detailed Hall-effect measurements of thin films of ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}$ above and below the metal-insulator transition. In the metallic ferromagnetic regime, we find a temperature-independent holelike nominal charge-carrier density ${n}_{h}^{*}=1.3$ per unit cell, consistent with a partly compensated Fermi surface. The mobility is only 92 ${\mathrm{mm}}^{2}/\mathrm{V}\mathrm{}\mathrm{s}$ at 4 K, and decreases with increasing temperature. Huge negative magnetoresistivity results from an increase in mobility. In low magnetic fields or at high temperatures, an anomalous electronlike contribution dominates the Hall voltage. For possible side …

2018

We apply homogenization theory to calculate the effective electric conductivity and Hall coefficient tensor of passive three-dimensionally periodic metamaterials subject to a weak external static homogeneous magnetic field. We not only allow for variations of the conductivity and the Hall coefficient of the constituent material(s) within the metamaterial unit cells, but also for spatial variations of the magnetic permeability. We present four results. First, our findings are consistent with previous numerical calculations for finite-size structures as well as with recent experiments. This provides a sound theoretical justification for describing such metamaterials in terms of effective mate…

Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compoundMn1.5FeV0.5Al

2017

The Slater-Pauling rule states that $L{2}_{1}$ Heusler compounds with 24 valence electrons never exhibit a total spin magnetic moment. In the case of strongly localized magnetic moments at one of the atoms (here Mn) they will exhibit a fully compensated half-metallic ferrimagnetic state instead, in particular, when symmetry does not allow for antiferromagnetic order. With the aid of magnetic and anomalous Hall effect measurements, it is experimentally demonstrated that ${\mathrm{Mn}}_{1.5}{\mathrm{V}}_{0.5}\mathrm{FeAl}$ follows such a scenario. The ferrimagnetic state is tuned by the composition. A small residual magnetization, which arises due to a slight mismatch of the magnetic moments …

Spontaneous magnetism of quantum dot lattices.

2003

The magnetism of square lattices of quantum dots with up to 12 electrons per dot is studied using the spin-density functional formalism. At small values of the lattice constant, all lattices are nonmagnetic and gapless. When the lattice constant is increased, the shell structure of the single dots governs the magnetism of the lattice. At closed shells, the lattices are nonmagnetic and have a gap at the Fermi level. At the beginning and at the end of a shell, they become ferromagnetic and stay gapless up to large values of the lattice constant. Antiferromagnetism was observed only at midshell after a band gap was opened.

Tight-Binding Model for Spontaneous Magnetism of Quantum Dot Lattices

2003

We use a simple tight-binding model to study the magnetism of two-dimensional quantum dot lattices with 1 to 12 electrons per dot. The results show that in the middle of an electron shell the lattice favours antiferromagnetism while with nearly empty or full shells ferromagnetism is favoured. The size of the antiferromagnetic region increases with the coordination number of the dot. A one-dimensional dot lattice shows a spin-Peierls transition. The results for a square lattice are in good agreement with density functional calculations of Koskinen et al.

Magnetopolaron in a weakly elliptical InAs/GaAs quantum dot

2003

We study theoretically the properties of a polaron formed in a shallow, weakly elliptical, disk-shaped InAs/GaAs quantum dot in the presence of a magnetic field by using the Davydov's canonical transformation. Special attention is paid to the energy-level splitting due to the Frohlich interaction of an electron in a quantum dot with optical phonons near resonance. The polaron relaxation rates, including the anharmonicity induced channel, are analyzed for various confinement energies and magnetic field magnitudes, taking into account coherent polaronic effects.

Excitonic model for second-order resonant Raman scattering.

1994

A theoretical model for second-order resonant Raman scattering is presented. The effect of Coulomb interaction between electrons and holes is fully taken into account in the framework of the effective-mass approximation. By introducing discrete and continuous excitonic intermediate states in the Raman process, an explicit expression for the Raman scattering efficiency is given for long-range Fr\"ohlich electron-phonon interaction. The model developed can be used to evaluate Raman profiles around the resonant region. A closed-form expression for all matrix elements of the exciton-phonon interaction is obtained once the Coulomb problem for the relative electron-hole motion is separated in sph…

Metal Clusters, Quantum Dots, and Trapped Atoms

2010

In this chapter, we discuss the electronic structure of finite quantal systems on the nanoscale. After a few general remarks on the many-particle physics of the harmonic oscillator, likely being the most studied example for the many-body systems of finite quantal systems, we turn to the electronic structure of metal clusters. We discuss Jahn–Teller deformations for the so-called “ultimate” jellium model which assumes a complete cancelation of the electronic charge with the ionic background. Within this model, we are also able to understand the stable electronic shell structure of tetrahedral (three-dimensional) or triangular (two-dimensional [2D]) cluster geometries, resembling closed shell…