Search results for "Ferro"
showing 10 items of 2451 documents
Semiadiabatic High-Field Polarization Response in Ferroelectrics I: Hysteresis and Nonlinear Susceptibility
2004
Ginzburg-Landau theory for ferroelectric phase instability is combined with Langevin, Fokker-Planck and imaginary time Schrodinger equation techniques to model impact of thermal noise in the kinetics of ferroelectric polarization. The proposed real space/real time numerical method allows to efficiently simulating relaxation, dynamic hysteresis and general dielectric response.
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…
Antiferromagnetic Heisenberg chains with bond alternation and quenched disorder
2004
We consider S=1/2 antiferromagnetic Heisenberg chains with alternating bonds and quenched disorder, which represents a theoretical model of the compound CuCl_{2x}Br_{2(1-x)}(\gamma-{pic})_2. Using a numerical implementation of the strong disorder renormalization group method we study the low-energy properties of the system as a function of the concentration, x, and the type of correlations in the disorder. For perfect correlation of disorder the system is in the random dimer (Griffiths) phase having a concentration dependent dynamical exponent. For weak or vanishing disorder correlations the system is in the random singlet phase, in which the dynamical exponent is formally infinity. We disc…
Itinerant half-metallic ferromagnetsCo2TiZ(Z=Si, Ge, Sn):Ab initiocalculations and measurement of the electronic structure and transport properties
2010
This work reports on ab initio calculations and experiments on the half-metallic ferromagnetic Heusler compounds ${\text{Co}}_{2}\text{Ti}Z$ $(Z=\text{Si},\text{ }\text{Ge},\text{ }\text{Sn})$. Aim is a comprehensive study of the electronic-structure and thermoelectric properties. The impact of the variation in the main group element $Z$ on those properties is discussed. X-ray diffraction was performed on the compounds and the lattice parameters are compared to other ${\text{Co}}_{2}$-based compounds. Hard x-ray photoemission measurements were carried out and the results are compared to the calculated electronic structure. The experimentally determined electronic structure, magnetic propert…
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 …
Combined effect of magnetic field and charge current on antiferromagnetic domain-wall dynamics
2017
We theoretically examine a cross effect of magnetic field and charge current on antiferromagnetic domain wall dynamics. Since antiferromagnetic materials are largely insensitive to external magnetic fields in general, charge current has been shown recently as an alternative and efficient way to manipulate antiferromagnets. We find a new role of the magnetic field in the antiferromagnetic dynamics that appears when it is combined with charge current, demonstrating a domain wall motion in the presence of both field and current. We show that a spatially varying magnetic field can shift the current-driven domain-wall velocity, depending on the domain-wall structure and the direction of the fiel…
High Antiferromagnetic Domain Wall Velocity Induced by Néel Spin-Orbit Torques.
2016
We demonstrate the possibility to drive an antiferromagnetic domain wall at high velocities by fieldlike Neel spin-orbit torques. Such torques arise from current-induced local fields that alternate their orientation on each sublattice of the antiferromagnet and whose orientation depends primarily on the current direction, giving them their fieldlike character. The domain wall velocities that can be achieved by this mechanism are 2 orders of magnitude greater than the ones in ferromagnets. This arises from the efficiency of the staggered spin-orbit fields to couple to the order parameter and from the exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads to a low doma…
Discriminating antiferromagnetic signatures in systems of ultracold fermions by tunable geometric frustration
2013
Recently, it has become possible to tune optical lattices continuously between square and triangular geometries. We compute thermodynamics and spin correlations in the corresponding Hubbard model using a determinant quantum Monte Carlo technique and show that the frustration effects induced by the variable hopping terms can be clearly separated from concomitant bandwidth changes by a proper rescaling of the interaction. An enhancement of the double occupancy by geometric frustration signals the destruction of nontrivial antiferromagnetic correlations at weak coupling and entropy $s\ensuremath{\lesssim}\mathrm{ln}(2)$ (and restores Pomeranchuk cooling at strong frustration), paving the way t…
Momentum structure of the self-energy and its parametrization for the two-dimensional Hubbard model
2016
We compute the self-energy for the half-filled Hubbard model on a square lattice using lattice quantum Monte Carlo simulations and the dynamical vertex approximation. The self-energy is strongly momentum dependent, but it can be parametrized via the non-interacting energy-momentum dispersion $\varepsilon_{\mathbf{k}}$, except for pseudogap features right at the Fermi edge. That is, it can be written as $\Sigma(\varepsilon_{\mathbf{k}},\omega)$, with two energy-like parameters ($\varepsilon$, $\omega$) instead of three ($k_x$, $k_y$ and $\omega$). The self-energy has two rather broad and weakly dispersing high energy features and a sharp $\omega= \varepsilon_{\mathbf{k}}$ feature at high tem…
Properties of the interface in the confined Ising magnet with competing surface fields
2007
Abstract A two-dimensional magnetic Ising system confined in an L × D geometry ( L ⪡ D ) in the presence of competing magnetic fields (h) acting at opposite walls along the D -direction, exhibits an interface between domains of different orientation that run parallel to the walls. In the limit L → ∞ , this interface undergoes a wetting transition that occurs at the critical curve T w ( h ) , so that for T T w ( h ) such an interface is bound to the walls, while for T w ( h ) ⩽ T T cb the interface is freely fluctuating around the center of the film, where T cb is the bulk critical temperature. By considering both short- and long-range magnetic fields acting at the walls, we study the diverg…