The Experts below are selected from a list of 1635 Experts worldwide ranked by ideXlab platform

Lior Klein - One of the best experts on this subject based on the ideXlab platform.

  • thickness dependence of the Resistivity Tensor in epitaxial magnetite thin films
    2013
    Co-Authors: Netanel Naftalis, J. A. Moyer, Yishai Shperber, C H Ahn, Lior Klein
    Abstract:

    We report a systematic study of the thickness dependence of the Resistivity Tensor of epitaxial thin films of magnetite (Fe3O4). We find that decreasing film thickness decreases the relative magnitude of the terms related to crystal symmetry but increases their field dependence. We attribute this behavior to the presence of antiphase boundaries in thin films of magnetite and the dependence of their density on the film thickness.

  • Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films
    2011
    Co-Authors: Netanel Naftalis, A. Kaplan, Moty Schultz, Carlos A. F. Vaz, J. A. Moyer, Charles H. Ahn, Lior Klein
    Abstract:

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system. We also show that the AMR exhibit sign reversal as a function of temperature, and that it shows significant field dependence without saturation up to 9 T. Our results provide a unified description of the anisotropic magnetoresistance effects in epitaxial magnetite films and illustrate the need for a full determination of the Resistivity Tensor in crystalline systems.

Netanel Naftalis - One of the best experts on this subject based on the ideXlab platform.

  • thickness dependence of the Resistivity Tensor in epitaxial magnetite thin films
    2013
    Co-Authors: Netanel Naftalis, J. A. Moyer, Yishai Shperber, C H Ahn, Lior Klein
    Abstract:

    We report a systematic study of the thickness dependence of the Resistivity Tensor of epitaxial thin films of magnetite (Fe3O4). We find that decreasing film thickness decreases the relative magnitude of the terms related to crystal symmetry but increases their field dependence. We attribute this behavior to the presence of antiphase boundaries in thin films of magnetite and the dependence of their density on the film thickness.

  • Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films
    2011
    Co-Authors: Netanel Naftalis, A. Kaplan, Moty Schultz, Carlos A. F. Vaz, J. A. Moyer, Charles H. Ahn, Lior Klein
    Abstract:

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system. We also show that the AMR exhibit sign reversal as a function of temperature, and that it shows significant field dependence without saturation up to 9 T. Our results provide a unified description of the anisotropic magnetoresistance effects in epitaxial magnetite films and illustrate the need for a full determination of the Resistivity Tensor in crystalline systems.

Gian Paolo Beretta - One of the best experts on this subject based on the ideXlab platform.

  • steepest entropy ascent model for far non equilibrium thermodynamics unified implementation of the maximum entropy production principle
    2014
    Co-Authors: Gian Paolo Beretta
    Abstract:

    By suitable reformulations, we cast the mathematical frameworks of several well-known different approaches to the description of non-equilibrium dynamics into a unified formulation valid in all these contexts, which extends to such frameworks the concept of Steepest Entropy Ascent (SEA) dynamics introduced by the present author in previous works on quantum thermodynamics. Actually, the present formulation constitutes a generalization also for the quantum thermodynamics framework. The analysis emphasizes that in the SEA modeling principle a key role is played by the geometrical metric with respect to which to measure the length of a trajectory in state space. In the near thermodynamic equilibrium limit, the metric Tensor turns is directly related to the Onsager's generalized Resistivity Tensor. Therefore, through the identification of a suitable metric field which generalizes the Onsager generalized resistance to the arbitrarily far non-equilibrium domain, most of the existing theories of non-equilibrium thermodynamics can be cast in such a way that the state exhibits the spontaneous tendency to evolve in state space along the path of SEA compatible with the conservation constraints and the boundary conditions. The resulting unified family of SEA dynamical models are all intrinsically and strongly consistent with the second law of thermodynamics. The nonnegativity of the entropy production is a general and readily proved feature of SEA dynamics. In several of the different approaches to non-equilibrium description we consider here, the SEA concept has not been investigated before. We believe it defines the precise meaning and the domain of general validity of the so-called Maximum Entropy Production principle. Therefore, it is hoped that the present unifying approach may prove useful in providing a fresh basis for effective, thermodynamically consistent, numerical models and theoretical treatments of irreversible conservative relaxation towards equilibrium from far non-equilibrium states. The mathematical frameworks are: A) Statistical or Information Theoretic Models of Relaxation; B) Small-Scale and Rarefied Gases Dynamics (i.e., kinetic models for the Boltzmann equation); C) Rational Extended Thermodynamics, Macroscopic Non-Equilibrium Thermodynamics, and Chemical Kinetics; D) Mesoscopic Non-Equilibrium Thermodynamics, Continuum Mechanics with Fluctuations; E) Quantum Statistical Mechanics, Quantum Thermodynamics, Mesoscopic Non-Equilibrium Quantum Thermodynamics, and Intrinsic Quantum Thermodynamics.

  • steepest entropy ascent model for far nonequilibrium thermodynamics unified implementation of the maximum entropy production principle
    2014
    Co-Authors: Gian Paolo Beretta
    Abstract:

    By suitable reformulations, we cast the mathematical frameworks of several well-known different approaches to the description of nonequilibrium dynamics into a unified formulation valid in all these contexts, which extends to such frameworks the concept of steepest entropy ascent (SEA) dynamics introduced by the present author in previous works on quantum thermodynamics. Actually, the present formulation constitutes a generalization also for the quantum thermodynamics framework. The analysis emphasizes that in the SEA modeling principle a key role is played by the geometrical metric with respect to which to measure the length of a trajectory in state space. In the near-thermodynamic-equilibrium limit, the metric Tensor is directly related to the Onsager's generalized Resistivity Tensor. Therefore, through the identification of a suitable metric field which generalizes the Onsager generalized resistance to the arbitrarily far-nonequilibrium domain, most of the existing theories of nonequilibrium thermodynamics can be cast in such a way that the state exhibits the spontaneous tendency to evolve in state space along the path of SEA compatible with the conservation constraints and the boundary conditions. The resulting unified family of SEA dynamical models is intrinsically and strongly consistent with the second law of thermodynamics. The non-negativity of the entropy production is a general and readily proved feature of SEA dynamics. In several of the different approaches to nonequilibrium description we consider here, the SEA concept has not been investigated before. We believe it defines the precise meaning and the domain of general validity of the so-called maximum entropy production principle. Therefore, it is hoped that the present unifying approach may prove useful in providing a fresh basis for effective, thermodynamically consistent, numerical models and theoretical treatments of irreversible conservative relaxation towards equilibrium from far nonequilibrium states. The mathematical frameworks we consider are the following: (A) statistical or information-theoretic models of relaxation; (B) small-scale and rarefied gas dynamics (i.e., kinetic models for the Boltzmann equation); (C) rational extended thermodynamics, macroscopic nonequilibrium thermodynamics, and chemical kinetics; (D) mesoscopic nonequilibrium thermodynamics, continuum mechanics with fluctuations; and (E) quantum statistical mechanics, quantum thermodynamics, mesoscopic nonequilibrium quantum thermodynamics, and intrinsic quantum thermodynamics.

J. A. Moyer - One of the best experts on this subject based on the ideXlab platform.

  • thickness dependence of the Resistivity Tensor in epitaxial magnetite thin films
    2013
    Co-Authors: Netanel Naftalis, J. A. Moyer, Yishai Shperber, C H Ahn, Lior Klein
    Abstract:

    We report a systematic study of the thickness dependence of the Resistivity Tensor of epitaxial thin films of magnetite (Fe3O4). We find that decreasing film thickness decreases the relative magnitude of the terms related to crystal symmetry but increases their field dependence. We attribute this behavior to the presence of antiphase boundaries in thin films of magnetite and the dependence of their density on the film thickness.

  • Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films
    2011
    Co-Authors: Netanel Naftalis, A. Kaplan, Moty Schultz, Carlos A. F. Vaz, J. A. Moyer, Charles H. Ahn, Lior Klein
    Abstract:

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system. We also show that the AMR exhibit sign reversal as a function of temperature, and that it shows significant field dependence without saturation up to 9 T. Our results provide a unified description of the anisotropic magnetoresistance effects in epitaxial magnetite films and illustrate the need for a full determination of the Resistivity Tensor in crystalline systems.

C Bouard - One of the best experts on this subject based on the ideXlab platform.

  • large enhancement of the spin hall effect in au by side jump scattering on ta impurities
    2017
    Co-Authors: P Laczkowski, Yu Fu, Huaiwen Yang, J C Rojassanchez, P Noel, V T Pham, G Zahnd, C Deranlot, S Collin, C Bouard
    Abstract:

    We present measurements of the Spin Hall Eect (SHE) in AuW and AuTa alloys for a large range of W or Ta concentrations by combining experiments on lateral spin valves and Ferromagnetic-Resonance/spin pumping technique. The main result is the identication of a large enhancement of the Spin Hall Angle (SHA) by the side-jump mechanism on Ta impurities, with a SHA as high as + 0.5 (i.e 50%) for about 10% of Ta. In contrast the SHA in AuW does not exceed + 0.15 and can be explained by intrinsic SHE of the alloy without signicant extrinsic contribution from skew or side-jump scattering by W impurities. The AuTa alloys, as they combine a very large SHA with a moderate Resistivity (smaller than 85 µΩ.cm), are promising for spintronic devices exploiting the SHE. A goal of spintronics is to generate, manipulate and detect spin currents for the transfer and manipulation of information, thus allowing faster and low-energy consuming operations. Since the discovery of the Giant Magnetoresistance a "classical" way to produce spin currents was to take advantage of ferromagnetic materials and their two different spin channel conductivities [1, 2]. In the last decade the rediscovery and study of spin orbit interaction eects brought new insights into creation mechanisms of spin currents. Among all mechanisms the spin Hall eect (SHE) focused a lot of attention as it allows the generation of spin currents from charge current and vice versa [3]. Despite being observed only a decade ago [46] these eects are already ubiquitous within the Spintronics as standard spin-current generators and detectors [7 9]. The conversion coecient between charge and spin currents is called the spin Hall angle (SHA) and is dened as Θ SHE = ρ xy /ρ xx , ratio of the non-diagonal and diagonal terms of the Resistivity Tensor. One of the main interests of the SHE is to provide a new paradigm for Spintronics where non-magnetic materials becomes active spin current source and detector. Until now most of the reports focused on single heavy metals and intrinsic SHE mechanisms, the main materials of interest being: Pt, Ta, W, and some oxydes. With intrinsic mechanisms the SHA is typically proportional to the Resistivity of the heavy metal, and generally, a large value of the SHA is associated with a high Resistivity (i.e.-0.3 for the SHA in β − W is associated with 263 µΩ.cm [10]) which limits the current density and the resulting spin transfer torques on the mag-netisation of an adjacent metallic ferromagnetic material. Extrinsic SHE mechanisms associated with the spin dependent scattering on impurities or defects are an alternative to generate transverse spin currents [11]. Two particular scattering mechanisms have been identied: the skew scattering [12] providing a non-diagonal term of the Resistivity Tensor proportional to the longitudinal Resistivity (ρ xy ∝ ρ xx) and the side jump [13] for which the non-diagonal term is proportional to the square of the Resistivity (ρ xy ∝ ρ 2 xx). For instance, the skew scattering mechanism have been observed in CuIr, CuBi, CuPb alloys (SHA=0.02,-0.24,-0.13, resp.) [14, 15]. The intrinsic mechanism from Berry curvature in the conduction band gives the same dependence ρ xy ∝ ρ 2 xx as the side-jump contribution so that, for example the SHE of AuPt (SHA=0.3 at max.) alloys could be explained by a predominant intrinsic eect rather than ascribed to side-jump[16]. In this letter we present a study of Au-based alloys with W and T a impurities. We demonstrate that the side-jump scattering mechanism dominates in AuTa alloys, and generates high spin Hall angles (up to + 0.5) with the additional advantage of resistivities (ρ AuT a < 85µΩ.cm) smaller than in most materials with SHA in the same range. By contrast in AuW alloys the SHE is mainly due to only the intrinsic mechanism and is denitely smaller than in AuTa. This dierence between AuTa and AuW is supported by ab − initio calculations. The alloys were fabricated by DC magnetron sputtering by co-deposition of the two pure materials. The concentration in atomic purcent were determined by chemical analyzes (proton or electron induced X-ray emission) and from the depo-sition rate of each species. We control the alloy-ing through the increase of the Resistivity as the