25 research outputs found
The skyrmion-bubble transition in a ferromagnetic thin film
Magnetic skyrmions and bubbles, observed in ferromagnetic thin films with
perpendicular magnetic anisotropy, are topological solitons which differ by
their characteristic size and the balance in the energies at the origin of
their stabilisation. However, these two spin textures have the same topology
and a continuous transformation between them is allowed. In the present work,
we derive an analytical model to explore the skyrmion-bubble transition. We
evidence a region in the parameter space where both topological soliton
solutions coexist and close to which transformations between skyrmion and
bubbles are observed as a function of the magnetic field. Above a critical
point, at which the energy barrier separating both solutions vanishes, only one
topological soliton solution remains, which size can be continuously tuned from
micrometer to nanometer with applied magnetic field
A quantitative description of skyrmions in ultrathin ferromagnetic films and rigidity of degree harmonic maps from to
We characterize skyrmions in ultrathin ferromagnetic films as local
minimizers of a reduced micromagnetic energy appropriate for quasi
two-dimensional materials with perpendicular magnetic anisotropy and
interfacial Dzyaloshinskii-Moriya interaction. The minimization is carried out
in a suitable class of two-dimensional magnetization configurations that
prevents the energy from going to negative infinity, while not imposing any
restrictions on the spatial scale of the configuration. We first demonstrate
existence of minimizers for an explicit range of the model parameters when the
energy is dominated by the exchange energy. We then investigate the conformal
limit, in which only the exchange energy survives and identify the asymptotic
profiles of the skyrmions as degree 1 harmonic maps from the plane to the
sphere, together with their radii, angles and energies. A byproduct of our
analysis is a quantitative rigidity result for degree harmonic maps
from the two-dimensional sphere to itself
Theory of magnetic field-stabilized compact skyrmions in thin film ferromagnets
We present a micromagnetic theory of compact magnetic skyrmions under applied
magnetic field that accounts for the full dipolar energy and the interfacial
Dzyaloshinskii-Moryia interaction (DMI) in the thin film regime. Asymptotic
analysis is used to derive analytical formulas for the parametric dependence of
the skyrmion size and rotation angle, as well as the energy barriers for
collapse and bursting, two processes that lead to a finite skyrmion lifetime.
We demonstrate the existence of a new regime at low DMI, in which the skyrmion
is stabilized by a combination of non-local dipolar interaction and a magnetic
field applied parallel to its core, and discuss the conditions for an
experimental realization of such field-stabilized skyrmions
Switching probability sub-distributions and asymmetric magnetization reversal in FePt nanostructures
International audienceThe coercive field statistics in FePt nanostructures reveals the existence of multiple switching probability sub-distributions that can be asymmetric with respect to the field orientation. Each sub-distribution is correlated with an individual magnetization reversal path whose selection cannot happen at the magnetization reversal in negative (positive) field but rather at the moment of applying the initial positive (negative) magnetic field. This serves to determine the reference magnetic state from which reversal in negative (positive) field will develop. The disappearance of the asymmetric sub-distributions upon increasing the initial magnetic field μ0Hmax supports this model. However, the sub-distributions remaining at high μ0Hmax are not necessarily those characterized by the highest coercive field. This is attributed to the fact that the initial magnetization state hierarchy and the coercive field hierarchy are essentially decorrelated
Electric-field effect on coercivity distributions in FePt magneto-electric devices
International audienceWe have investigated the contribution of stochastic thermally activated processes to the electric-field effects on coercivity in FePt. Coercive field distributions were measured under different gate voltages in solid-state field-effect structures. For low voltages a shift in the coercive field distribution can be observed, however, it is not larger than the width of the distribution. Higher oltages are needed to obtain the splitting from the negative (zero) voltage distribution allowing for the unambiguous characterization of the electric-field effect. A virtual unipolarity in the electric-field effect has been identified as a feature introduced by the dielectric layer that disappears upon annealing
Voltage control of magnetism in ferromagnetic structures (Conference Paper)
San Diego, California, United StatesInternational audienceUntil now, spintronics devices have relied on polarized currents, which still generate relatively high dissipation, particularly for nanodevices based on DW motion. A novel solution to further reduce power consumption is emerging, based on electric field (E) gating to control the magnetic state. Here, we will describe the state of the art and our recent experiments on voltage induced changes in the magnetic properties of ferromagnetic metals. A thorough description of the advances in terms of control of intrinsic properties such as magnetic anisotropy and ferromagnetic transition temperature as well as in intrinsic properties like coercive field and domain wall motion will be presented. Additionally, a section will be dedicated to the summary of the key aspects concerning the fabrication and performance of magneto-electric field-effect devices
The skyrmion switch: turning magnetic skyrmion bubbles on and off with an electric field
Nanoscale magnetic skyrmions are considered as potential information carriers
for future spintronics memory and logic devices. Such applications will require
the control of their local creation and annihilation, which involves so far
solutions that are either energy consuming or difficult to integrate. Here we
demonstrate the control of skyrmion bubbles nucleation and annihilation using
electric field gating, an easily integrable and potentially energetically
efficient solution. We present a detailed stability diagram of the skyrmion
bubbles in a Pt/Co/oxide trilayer and show that their stability can be
controlled via an applied electric field. An analytical bubble model, with the
Dzyaloshinskii-Moriya interaction imbedded in the domain wall energy, account
for the observed electrical skyrmion switching effect. This allows us to unveil
the origin of the electrical control of skyrmions stability and to show that
both magnetic dipolar interaction and the Dzyaloshinskii-Moriya interaction
play an important role in the skyrmion bubble stabilization
Transport à un électron et effets magnéto-Coulomb dans une nanoparticule unique
Cette thèse s'inscrit dans le cadre de l'évolution récente de la spintronique en basse dimension : la nanospintronique. L'objectif de cette thèse a été l'étude expérimentale de l'interaction entre magnétisme et transport à un électron, nommément effets magnéto-Coulomb, dans des nanostructures magnétiques contenant des nanoparticules uniques. En utilisant une technique de nanoindentation résistivo-contrôlée développée au laboratoire, de tels échantillons constitués d'une nanoparticule métallique (or, cuivre ou aluminium) de quelques nanomètres de diamètre, reliée via des barrières tunnel d'alumine a des électrodes de cobalt ont été élaborés. Les échantillons ont présenté les caractéristiques typiques attendue du transport à un électron (effet de blocage de Coulomb) à travers une nanoparticule unique. De fortes magnéto-résistances ont été observées. Des effets de transport dépendant du spin et d'accumulation de spin liés à une augmentation du temps de vie du spin dans les nanoparticules métalliques ont été mis en évidence. De plus, un autre mécanisme de magnéto transport, ayant pour origine l'anisotropie magnétique de l'électrode et agissant comme une "grille" sur l'îlot, a été observé.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Programs used to generate the figures in arXiv:1712.03154v2 "The skyrmion-bubble transition in ferromagnetic thin films"
This release contains all the data for the study of the skyrmion-bubble transition in a ferromagnetic thin film including a S factor calculator and programs used to generate the figures