The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Shufeng Zhang - One of the best experts on this subject based on the ideXlab platform.

  • domain wall dynamics and spin wave excitations with spin transfer torques
    Physical Review Letters, 2004
    Co-Authors: Shufeng Zhang
    Abstract:

    A generalization of spin-transfer torques in ferroMagnetic structures is proposed. For a spatially nonuniform magnetization, the spin torque has a form nearly identical to that in Magnetic Multilayers. We show that the domain-wall motion driven by the current has many unique features that do not exist in the conventional domain-wall motion driven by a Magnetic field. We also demonstrate that the spin torque can generate bulk and surface spin excitations that have been seen in point-contact experiments.

  • self consistent treatment of nonequilibrium spin torques in Magnetic Multilayers
    Physical Review B, 2003
    Co-Authors: Asya Shpiro, Peter M Levy, Shufeng Zhang
    Abstract:

    It is known that the transfer of spin angular momenta between current carriers and local moments occurs near the interface of Magnetic layers when their moments are noncollinear. However, to determine the magnitude of the transfer, one should calculate the spin transport properties far beyond the interface regions. Based on the spin-diffusion equation, we present a self-consistent approach to evaluate the spin torque for a number of layered structures. One of the salient features is that the longitudinal and transverse components of spin accumulations are intertwined from one layer to the next, due to the presence of the much longer longitudinal spin-diffusion length and thus, the spin torque could be significantly amplified with respect to treatments which concentrate solely on the transport at the interface. We conclude that bare spin currents do not properly estimate the spin angular momentum transferred between the Magnetic background; the spin transfer that occurs at interfaces should be self-consistently determined by embedding it in our globally diffuse transport calculations.

  • Spin Hall Effect in the Presence of Spin Diffusion
    Physical review letters, 2000
    Co-Authors: Shufeng Zhang
    Abstract:

    Hirsch [Phys. Rev. Lett. 83, 1834 (1999)] recently proposed a spin Hall effect based on the anomalous scattering mechanism in the absence of spin-flip scattering. Since the anomalous scattering causes both anomalous currents and a finite spin-diffusion length, we derive the spin Hall effect in the presence of spin diffusion from a semiclassical Boltzmann equation. When the formulation is applied to certain metals and semiconductors, the magnitude of the spin Hall voltage due to the spin accumulation is found to be much larger than that of Magnetic Multilayers. An experiment is proposed to measure this spin Hall effect.

Sa Nikitov - One of the best experts on this subject based on the ideXlab platform.

  • diameter independent skyrmion hall angle observed in chiral Magnetic Multilayers
    Nature Communications, 2020
    Co-Authors: Aj Huxtable, Av Sadovnikov, Sa Nikitov, Katharina Zeissler, Simone Finizio, Craig Barton, Jamie Massey, Jorg Raabe
    Abstract:

    Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion-inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterised by an angle with respect to the applied force direction. This skyrmion Hall angle is predicted to be skyrmion diameter-dependent. In contrast, our experimental study finds that the skyrmion Hall angle is diameter-independent for skyrmions with diameters ranging from 35 to 825 nm. At an average velocity of 6 ± 1 ms−1, the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local Magnetic configuration. Magnetic skyrmions are promising objects for future spintronic devices. However, a better understanding of their dynamics is required. Here, the authors show that in contrast to predictions the skyrmion Hall angle is independent of their diameter and motion is dominated by disorder and skyrmion-skyrmion interactions in the system.

  • Diameter-independent skyrmion Hall angle observed in chiral Magnetic Multilayers
    Nature Research, 2020
    Co-Authors: Zeissler K, Finizio S, Barton C, Aj Huxtable, Massey J, Raabe J, Av Sadovnikov, Sa Nikitov, Brearton R, Hesjedal T
    Abstract:

    Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterised by an angle with respect to the applied force direction. This skyrmion Hall angle is predicted to be skyrmion diameter dependent. In contrast, our experimental study finds that the skyrmion Hall angle is diameter independent for skyrmions with diameters ranging from 35 to 825 nm. At an average velocity of 6 ± 1 ms−1, the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local Magnetic configuration

  • diameter independent skyrmion hall angle in the plastic flow regime observed in chiral Magnetic Multilayers
    arXiv: Mesoscale and Nanoscale Physics, 2019
    Co-Authors: Katharina Zeissler, Aj Huxtable, Av Sadovnikov, Sa Nikitov, Simone Finizio, Craig Barton, Jamie Massey, Jorg Raabe, Richard Brearton, T Hesjedal
    Abstract:

    Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion-inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterized by an angle with respect to the applied force direction. This skyrmion Hall angle was believed to be skyrmion diameter-dependent. In contrast, our experimental study finds that within the plastic flow regime the skyrmion Hall angle is diameter-independent. At an average velocity of 6 $\pm$ 1 m/s the average skyrmion Hall angle was measured to be 9° $\pm$ 2°. In fact, in the plastic flow regime, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local Magnetic configuration.

Yuriy Mokrousov - One of the best experts on this subject based on the ideXlab platform.

  • engineering the dynamics of topological spin textures by anisotropic spin orbit torques
    Physical Review B, 2020
    Co-Authors: Frank Freimuth, Yuriy Mokrousov, Jairo Sinova, Janphilipp Hanke, Bertrand Dupe, Mathias Klaui
    Abstract:

    Integrating topologically stabilized Magnetic textures such as skyrmions as nanoscale information carriers into future technologies requires the reliable control by electric currents. Here, we uncover that the relevant skyrmion Hall effect, which describes the deflection of moving skyrmions from the current flow direction, acquires important corrections owing to anisotropic spin-orbit torques that alter the dynamics of topological spin structures. Thereby, we propose a viable means for manipulating the current-induced motion of skyrmions and antiskyrmions. Based on these insights, we demonstrate by first-principles calculations and symmetry arguments that the motion of spin textures can be tailored by materials design in Magnetic Multilayers of Ir/Co/Pt and Au/Co/Pt. Our work advances the understanding of the current-induced dynamics of these Magnetic textures, which underlies a plethora of memory and logic applications.

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

  • modeling the shape of axisymmetric skyrmions in Magnetic Multilayers
    Physical review applied, 2018
    Co-Authors: William Legrand, Nathan Ronceray, Nicolas Reyren, Davide Maccariello, Vincent Cros, A Fert
    Abstract:

    Magnetic skyrmions (arrangements of spins featuring topological properties) are candidates to implement information bits in devices for combined data storage and logic processing. A prerequisite is the further optimization of the host Magnetic Multilayers, to obtain sufficiently stable and mobile skyrmions below 10 nm in size. This study develops an extensive model of skyrmions in Magnetic Multilayers, allowing analysis or prediction of their size, Magnetic structure, and dynamical behavior. This model establishes guidelines for optimizing multilayer properties on the way to applications of Magnetic skyrmions.

  • Modeling the Shape of Axisymmetric Skyrmions in Magnetic Multilayers
    Physical Review Applied, 2018
    Co-Authors: William Legrand, Nathan Ronceray, Nicolas Reyren, Davide Maccariello, Vincent Cros, A Fert
    Abstract:

    We present a comprehensive microMagnetic model of isolated axisymmetric skyrmions in Magnetic Multilayers with perpendicular anisotropy. Most notably, the essential role of the internal dipolar field is extensively considered with a minimum amount of assumptions on the magnetization profiles. The tridi-mensional structure of the multilayered skyrmions is modeled by their radial profiles in each layer. We first compare the results of the model against a full microMagnetic description in Cartesian coordinates. Our model combines information on both layer-dependent size and chirality of the skyrmions. We also provide a convenient criterion in order to characterize the stability of skyrmions against anisotropic elongations that would break their cylindrical symmetry, which allows us to confirm the stability of the determined solutions. Because this model is able to treat magnetization configurations twisted through the thickness of multilayered skyrmions, it can provide predictions on any potential hybrid chirality in skyrmions due to the interplay of Dzyaloshinskii-Moriya and dipolar interactions in Multilayers. We finally apply the results of our model to the description of the current-driven dynamics of hybrid chiral skyrmions. Using the Thiele formalism, we show that we can predict the forces exerted on the multilayered skyrmions by vertical spin-polarized currents, which provides a method to conform hybrid skyrmion chiralities and spin-current injection geometries in order to optimize skyrmion motion in Multilayers, to the aim of maximizing the current-induced velocity, or canceling the skyrmion Hall angle.

  • hybrid chiral domain walls and skyrmions in Magnetic Multilayers
    Science Advances, 2018
    Co-Authors: William Legrand, Nicolas Reyren, Davide Maccariello, Vincent Cros, Jeanyves Chauleau, Sophie Collin, K Bouzehouane, Nicolas Jaouen, A Fert
    Abstract:

    Noncollinear spin textures in ferroMagnetic ultrathin films are currently the subject of renewed interest since the discovery of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange interaction selects a given chirality for the spin textures and allows stabilizing configurations with nontrivial topology including chiral domain walls (DWs) and Magnetic skyrmions. Moreover, it has many crucial consequences on the dynamical properties of these topological structures. In recent years, the study of noncollinear spin textures has been extended from single ultrathin layers to Magnetic Multilayers with broken inversion symmetry. This extension of the structures in the vertical dimension allows room temperature stability and very efficient current-induced motion for both Neel DWs and skyrmions. We show how, in these multilayered systems, the interlayer interactions can actually lead to hybrid chiral magnetization arrangements. The described thickness-dependent reorientation of DWs is experimentally confirmed by studying demagnetized Multilayers through circular dichroism in x-ray resonant Magnetic scattering. We also demonstrate a simple yet reliable method for determining the magnitude of the DMI from static domain measurements even in the presence of these hybrid chiral structures by taking into account the actual profile of the DWs. The existence of these novel hybrid chiral textures has far-reaching implications on how to stabilize and manipulate DWs, as well as skymionic structures in Magnetic Multilayers.

  • hybrid chiral domain walls and skyrmions in Magnetic Multilayers
    arXiv: Materials Science, 2017
    Co-Authors: William Legrand, Nicolas Reyren, Davide Maccariello, Vincent Cros, Jeanyves Chauleau, Sophie Collin, K Bouzehouane, Nicolas Jaouen, A Fert
    Abstract:

    Noncollinear spin textures in ferroMagnetic ultrathin films are currently the subject of renewed interest since the discovery of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange interaction selects a given chirality for the spin textures and allows stabilising configurations with nontrivial topology. Moreover, it has many crucial consequences on the dynamical properties of these topological structures, including chiral domain walls (DWs) and Magnetic skyrmions. In the recent years the study of noncollinear spin textures has been extended from single ultrathin layers to Magnetic Multilayers with broken inversion symmetry. This extension of the structures in the vertical dimension allows very efficient current-induced motion and room-temperature stability for both N\'eel DWs and skyrmions. Here we show how in such multilayered systems the interlayer interactions can actually lead to more complex, hybrid chiral magnetisation arrangements. The described thickness-dependent reorientation of DWs is experimentally confirmed by studying demagnetised Multilayers through circular dichroism in x-ray resonant Magnetic scattering. We also demonstrate a simple yet reliable method for determining the magnitude of the DMI from static domains measurements even in the presence of these hybrid chiral structures, by taking into account the actual profile of the DWs. The advent of these novel hybrid chiral textures has far-reaching implications on how to stabilise and manipulate DWs as well as skymionic structures in Magnetic Multilayers.

  • spin torque and waviness in Magnetic Multilayers a bridge between valet fert theory and quantum approaches
    Physical Review Letters, 2009
    Co-Authors: Valentin Rychkov, A Fert, Simone Borlenghi, Henri Jaffres, Xavier Waintal
    Abstract:

    We develop a simple theoretical framework for transport in Magnetic Multilayers, based on the Landauer-Buttiker scattering formalism and random matrix theory. A simple transformation allows one to go from the scattering point of view to theories expressed in terms of local currents and the electroMagnetic potential. In particular, our theory can be mapped onto the well-established classical Valet-Fert theory for collinear systems. For noncollinear systems, in the absence of spin-flip scattering, our theory can be mapped onto the generalized circuit theory. We apply our theory to the angular dependence of spin accumulation and spin torque in noncollinear spin valves.

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

  • currents and torques in metallic Magnetic Multilayers
    Journal of Magnetism and Magnetic Materials, 2002
    Co-Authors: J. C. Slonczewski
    Abstract:

    A theory is given for electron transport across a very thin non-Magnetic metallic spacer joining two ferroMagnetic metals whose moment vectors include a general angle. An assumed condition of negligible interfacial reflection for majority-spin electrons is approached by certain multilayer compositions including the experimentally important composition Co/Cu. Analytic formulas based on a non-spin-diagonal density operator inside the spacer connect the spin-channel currents and electro-chemical voltages across the spacer. The quantum-mechanically derived torques on sublayer moments agree with a previous macroscopic relation. The single additional parameter of the resulting macroscopic magnetoelectronic transport formulation depends only on bulk electron structure of the spacer. Illustrative application of the new connection formulas to the special case of two equal thin ferromagnets predicts closely related expressions for angular dependences of magnetoresistance and current-driven torque. A simple relation between magnetoresistance and asymmetry of exciting currents holds for this case.

  • Current-driven excitation of Magnetic Multilayers
    Journal of Magnetism and Magnetic Materials, 1996
    Co-Authors: J. C. Slonczewski
    Abstract:

    A new mechanism is proposed for exciting the Magnetic state of a ferromagnet. Assuming ballistic conditions and using WKB wave functions, we predict that a transfer of vectorial spin accompanies an electric current flowing perpendicular to two parallel Magnetic films connected by a normal metallic spacer. This spin transfer drives motions of the two magnetization vectors within their instantaneously common plane. Consequent new mesoscopic precession and switching phenomena with potential applications are predicted.

  • magnetostatic mechanism for field sensitivity of magnetoresistance in discontinous Magnetic Multilayers
    Journal of Magnetism and Magnetic Materials, 1994
    Co-Authors: J. C. Slonczewski
    Abstract:

    Abstract We derive an expression for the inter-layer magnetostatic coupling which governs the field-sensitivity of the giant magnetoresistance in the thin discontinous Magnetic Multilayers of composition (Ni80Fe20)/Ag recently discovered by T.L. Hylton and coworkers. This expression provides estimates of the width G of the Magnetic discontinuity needed to account for the external fields used to obtain the published experimental magnetoresistance data. The results are G = 10 A after the anneal which maximizes the saturation magnetoresistance and G ≈ 6 A after the anneal which maximizes its field-sensitivity.

  • mechanism of interlayer exchange in Magnetic Multilayers
    Journal of Magnetism and Magnetic Materials, 1993
    Co-Authors: J. C. Slonczewski
    Abstract:

    Abstract The spin-current method is used to calculate the oscillatory exchange energy that couples two semi-infinite ferromagnets with exchange-split parabolic bands which are joined by a nonMagnetic metallic spacer. A closed asymptotic formula extends the previous RKKY-type formula to the case in which the ferromagnets and spacer have different Fermi vectors. The predicted amplitude of oscillatory coupling increases steeply with Fermi vector or electron density in the spacer, as do the experimental trends reported by Parkin. Numerical computations relevant to iron support this closed formula and show that the amplitude of the biquadratic (J2 cos2θ) and higher-order corrections to the conventional -J1 cos θ form of energy is less than 2%.

  • origin of biquadratic exchange in Magnetic Multilayers invited
    Journal of Applied Physics, 1993
    Co-Authors: J. C. Slonczewski
    Abstract:

    We postulate localized‐electron states with unpaired spin located within or at the interfaces of an otherwise nonMagnetic metallic spacer layer. Loose exchange coupling of these spins to two ferromagnets mediates a non‐Heisenberg exchange coupling between them which includes a biquadratic term. A particular version of the model assumes that each interfacial layer of Magnetic atoms is weakly exchange coupled to the remainder of the ferromagnets. This model permits interpretation of the biquadratic‐coupling data of Gutierrez et al. for Fe/Al/Fe trilayers and of Fuss et al. for Fe/Au/Fe. According to this interpretation, the observed biquadratic coupling is intrinsic to the ideal multilayer structure rather than due to impurities or structural defects.