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J Z Sun - One of the best experts on this subject based on the ideXlab platform.

  • switching speed distribution of spin torque induced Magnetic Reversal
    Journal of Applied Physics, 2007
    Co-Authors: J Z Sun, Shuai Zhang
    Abstract:

    The switching probability of a single-domain ferromagnet under spin-current excitation is evaluated using the Fokker-Planck equation (FPE). In the case of uniaxial anisotropy, the FPE reduces to an ordinary differential equation in which the lowest eigenvalue λ1 determines the slowest switching events. We have calculated λ1 using both analytical and numerical methods. It is found that the previous model based on thermally distributed initial magnetization states [J. Z. Sun et al., Proc. SPIE 5359, 445 (2004)] can be accurately justified in some useful limiting conditions.

  • switching speed distribution of spin torque induced Magnetic Reversal
    arXiv: Materials Science, 2006
    Co-Authors: J Z Sun, Shuai Zhang
    Abstract:

    The switching probability of a single-domain ferromagnet under spin-current excitation is evaluated using the Fokker-Planck equation(FPE). In the case of uniaxial anisotropy, the FPE reduces to an ordinary differential equation in which the lowest eigenvalue $\lambda_1$ determines the slowest switching events. We have calculated $\lambda_1$ by using both analytical and numerical methods. It is found that the previous model based on thermally distributed initial magnetization states \cite{Sun1} can be accurately justified in some useful limiting conditions.

  • spin angular momentum transfer in current perpendicular nanoMagnetic junctions
    Ibm Journal of Research and Development, 2006
    Co-Authors: J Z Sun
    Abstract:

    Spin angular momentum transfer, or spin-transfer, describes the transfer of spin angular momentum between a spin-polarized current and a ferroMagnetic conductor. The angular momentum transfer exerts a torque (spin-current induced torque, or spin-torque) on the ferroMagnetic conductor. When its dimensions are reduced to less than 100 nm, the spin-torque can become comparable to the Magnetic damping torque at a spin-polarized current of high current density (above 106 A/cm2), giving rise to a new set of current-induced dynamic excitation and Magnetic switching phenomena. This has now been definitively observed in sub-100-nm current-perpendicular spin-valves and Magnetic tunnel junctions, and appears promising as a basis for direct write-address of a nanoMagnetic bit when the lateral bit size is reduced to well below 100 nm. An overview is presented in this paper of spin-transfer phenomena. The first part of the paper contains a brief introduction to spin-transfer, especially the characteristic dynamics associated with spin-torque. In the second part, several representative experiments are described. In the third part, a set of basic phenomenological models are introduced that describe experimental observations. The models also serve as a bridge for quantitative comparison between experiments and first-principles spin-polarized transport theory. In the last part of the paper, some device concepts based on spin-transfer-induced Magnetic excitation and Magnetic Reversal are described.

  • time resolved Reversal of spin transfer switching in a nanomagnet
    Physical Review Letters, 2004
    Co-Authors: R H Koch, J Z Sun
    Abstract:

    Time-resolved measurements of spin-transfer-induced (STI) magnetization Reversal were made in current-perpendicular spin-valve nanoMagnetic junctions subject to a pulsed current bias. These results can be understood within the framework of a Landau-Lifshitz-Gilbert equation that includes STI corrections and a Langevin random field for finite temperature. Comparison of these measurements with model calculations demonstrates that spin-transfer induced excitation is responsible for the observed Magnetic Reversal in these samples.

W R Branford - One of the best experts on this subject based on the ideXlab platform.

  • sculpting the spin wave response of artificial spin ice via microstate selection
    Physical Review B, 2019
    Co-Authors: Jack C Gartside, Daan M Arroo, W R Branford
    Abstract:

    Artificial spin ice (ASI) systems have emerged as promising hosts for magnonic applications due to a correspondence between their Magnetic configuration and spin dynamics. Though it has been demonstrated that spin-wave spectra are influenced by the ASI microstate the precise nature of this relationship has remained unclear. Recent advances in controlling the Magnetic configuration of ASI make harnessing the interplay between spin dynamics and the microstate achievable. This could allow diverse applications including reconfigurable magnonic crystals and programmable microwave filters. However, extracting any novel functionality requires a full understanding of the underlying spin-wave/microstate interaction. Here, we present a systematic analysis of how the microstate of a honeycomb ASI system affects its spin-wave spectrum through microMagnetic simulations. We find the spectrum to be highly tunable via the Magnetic microstate, allowing the (de)activation of spin-wave modes and band-gap tuning via Magnetic Reversal of individual nanoislands. Symmetries of ASI systems and the chirality of ``monopole'' defects are found to play important roles in determining the high-frequency Magnetic response.

  • low temperature and high field regimes of connected kagome artificial spin ice the role of domain wall topology
    Scientific Reports, 2016
    Co-Authors: Katharina Zeissler, Megha Chadha, Edmund Lovell, L. F. Cohen, W R Branford
    Abstract:

    Artificial spin ices are frustrated Magnetic nanostructures where single domain nanobars act as macrosized spins. In connected kagome artificial spin ice arrays, Reversal occurs along one-dimensional chains by propagation of ferroMagnetic domain walls through Y-shaped vertices. Both the vertices and the walls are complex chiral objects with well-defined topological edge-charges. At room temperature, it is established that the topological edge-charges determine the exact switching Reversal path taken. However, Magnetic Reversal at low temperatures has received much less attention and how these chiral objects interact at reduced temperature is unknown. In this study we use Magnetic force microscopy to image the Magnetic Reversal process at low temperatures revealing the formation of quite remarkable high energy remanence states and a change in the dynamics of the Reversal process. The implication is the breakdown of the artificial spin ice regime in these connected structures at low temperatures.

Claudia Felser - One of the best experts on this subject based on the ideXlab platform.

  • half metallic compensated ferrimagnetism with a tunable compensation point over a wide temperature range in the mn fe v al heusler system
    AIP Advances, 2017
    Co-Authors: Rolf Stinshoff, Gerhard H Fecher, Stanislav Chadov, Ajaya K Nayak, Benjamin Balke, Siham Ouardi, Tetsuya Nakamura, Claudia Felser
    Abstract:

    The cubic Heusler compound Mn1.5FeV0.5Al with the L21 Heusler structure is the first fully compensated half-metallic ferrimagnet with 24 valence electrons. The ferriMagnetic state can be tuned by changing the composition such that the compensation point appears at finite temperatures ranging from 0 K up to 226 K, while retaining half-metallicity in the system. In this paper, the structural, Magnetic and transport properties of the Mn-Fe-V-Al system are discussed. Magnetic Reversal and a change of sign of the anomalous Hall effect were observed at the compensation point, which gives rise to a sublattice spin-crossing. These materials present new possibilities for potential spintronic devices because of their advantageous properties such as imperceptibility to external fields, lower power consumption and ultrafast switching in the THz region.

  • completely compensated ferrimagnetism and sublattice spin crossing in the half metallic heusler compound mn 1 5 fev 0 5 al
    Physical Review B, 2017
    Co-Authors: Rolf Stinshoff, Gerhard H Fecher, Ajaya K Nayak, Benjamin Balke, Siham Ouardi, Tetsuya Nakamura, Yurii Skourski, Claudia Felser
    Abstract:

    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 in the different sublattices, results in a pronounced change of the temperature dependence of the ferrimagnet. A compensation point is confirmed by observation of Magnetic Reversal and sign change of the anomalous Hall effect. Theoretical models are presented that correlate the electronic structure and the compensation mechanisms of the different half-metallic ferriMagnetic states in the Mn-V-Fe-Al Heusler system.

  • completely compensated ferrimagnetism and sublattice spin crossing in the half metallic heusler compound mn1 5 fev0 5 al
    Physical Review B, 2017
    Co-Authors: Rolf Stinshoff, Gerhard H Fecher, Ajaya K Nayak, Benjamin Balke, Siham Ouardi, Tetsuya Nakamura, Yurii Skourski, Claudia Felser
    Abstract:

    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 in the different sublattices, results in a pronounced change of the temperature dependence of the ferrimagnet. A compensation point is confirmed by observation of Magnetic Reversal and sign change of the anomalous Hall effect. Theoretical models are presented that correlate the electronic structure and the compensation mechanisms of the different half-metallic ferriMagnetic states in the Mn-V-Fe-Al Heusler system.

Roy W. Chantrell - One of the best experts on this subject based on the ideXlab platform.

  • atomistic spin model simulation of Magnetic Reversal modes near the curie point
    Applied Physics Letters, 2010
    Co-Authors: Joseph Barker, Roy W. Chantrell, Richard F L Evans, Denise Hinzke, Ulrich Nowak
    Abstract:

    In order for the current increase in Magnetic storage density to continue, one must overcome the so-called Magnetic recording trilemma; namely, that smaller grains are required for higher data densities and to ensure their thermal stability, materials with a high anisotropy are required. The higher coercive field that this produces also becomes a limiting factor as the maximum field produced by the recording head is constrained by the saturation magnetization of the pole. One proposed solution to the trilemma is the use of heat assisted Magnetic recording HAMR, which utilizes the temperature dependence of the anisotropy to enable writing of materials with a high coercivity. For the highest anisotropy media, this will require heating to the Curie temperature TC of the material. Close to TC, longitudinal fluctuations in the magnetization can have a significant impact on the expected energy barriers and therefore the relaxation time of the magnetization. These effects become especially important when attempting to minimize the time to reverse the magnetization state of the media that will be important at higher storage densities.

  • the fluctuation field of ferroMagnetic materials
    Journal of Physics: Condensed Matter, 1997
    Co-Authors: A Lyberatos, Roy W. Chantrell
    Abstract:

    Starting from the basic constitutive equation that describes the Magnetic viscosity of a ferroMagnetic material, under the single assumption of a constant external field H, a connection is shown between the different expressions used to determine experimentally the fluctuation field . The simplest method uses the relation . If is invariant during the viscous decay of the magnetization, the relation may also be employed. The relaxation curves obtained at different fields, in this case, superimpose onto a single curve on renormalizing the time. An alternative treatment that considers explicitly the demagnetizing field is also presented. The theory is then applied to magneto-optic thin films, where two activation mechanisms are involved, assuming the absence of dispersion in the energy barriers, and also to the common case of relaxation by a single activation mechanism in the presence of a dispersion of the energy barriers. In both situations, it is shown that the fluctuation field may vary in strength during Magnetic Reversal. A method of classification of the hard ferroMagnetic materials, through experimental means, is suggested.

  • model of thermally activated magnetization Reversal in thin films of amorphous rare earth transition metal alloys
    Physical Review B, 1996
    Co-Authors: A Lyberatos, J Earl, Roy W. Chantrell
    Abstract:

    Monte Carlo simulations on a two-dimensional lattice of Magnetic dipoles have been performed to investigate the Magnetic Reversal by thermal activation in rare-earth-transition-metal (RE-TM) alloys. Three mechanisms of magnetization Reversal were observed: nucleation dominated growth, nucleation followed by the growth of Magnetic domains containing no seeds of unreversed magnetization, and nucleation followed by dendritic domain growth by successive branching in the motion of the domain walls. The domain structures are not fractal; however, the fractal dimension of the domain wall was found to be a good measure of the jaggedness of the domain boundary surface during the growth process. The effects of the demagnetizing field on the hysteretic and time-dependent properties of the thin films were studied and some limitations in the application of the Fatuzzo model on magneto-optic media are identified.

B L Gallagher - One of the best experts on this subject based on the ideXlab platform.

  • Magnetic Reversal under external field and current driven domain wall motion in ga mn as influence of extrinsic pinning
    New Journal of Physics, 2008
    Co-Authors: Kaiyou Wang, A C Irvine, J Wunderlich, K W Edmonds, A W Rushforth, R P Campion, C T Foxon, D A Williams, B L Gallagher
    Abstract:

    We investigate the anisotropy of Magnetic Reversal and current-driven domain wall motion in annealed Ga0.95Mn0.05As thin films and Hall bar devices with perpendicular Magnetic anisotropy. Hall bars with current direction along the [110] and crystallographic axes are studied. The [110] device shows larger coercive field than the device. Strong anisotropy is observed during Magnetic Reversal between [110]- and -directions. For both devices, the critical current required to depin a domain wall from an etch step is found to be strongly temperature-dependent, and can be described by a power-law dependence on the magnetization (M) with an exponent of 2.6±0.3. The domain wall motion is strongly influenced by the presence of local pinning centres.

  • Magnetic Reversal under external field and current driven domain wall motion in ga mn as influence of extrinsic pinning
    arXiv: Mesoscale and Nanoscale Physics, 2008
    Co-Authors: Kaiyou Wang, A C Irvine, J Wunderlich, K W Edmonds, A W Rushforth, R P Campion, C T Foxon, D A Williams, B L Gallagher
    Abstract:

    We investigate the anisotropy of Magnetic Reversal and current-driven domain wall motion in annealed Ga_0.95Mn_0.05As thin films and Hall bar devices with perpendicular Magnetic anisotropy. Hall bars with current direction along the [110] and [1-10] crystallographic axes are studied. The [110] device shows larger coercive field than the [1-10] device. Strong anisotropy is observed during Magnetic Reversal between [110] and [1-10] directions. A power law dependence is found for both devices between the critical current (JC) and the magnetization (M), with J_C is proportional to M^2.6. The domain wall motion is strongly influenced by the presence of local pinning centres.