61 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
Anisotropic magneto-Coulomb effect versus spin accumulation in a ferromagnetic single-electron device
We investigate the magneto-transport characteristics of nanospintronics
single-electron devices. The devices consist of single non-magnetic
nano-objects (nanometer size nanoparticles of Al or Cu) connected to Co
ferromagnetic leads. The comparison with simulations allows us attribute the
observed magnetoresistance to either spin accumulation or anisotropic
magneto-Coulomb effect (AMC), two effects with very different origins. The fact
that the two effects are observed in similar samples demonstrates that a
careful analysis of Coulomb blockade and magnetoresistance behaviors is
necessary in order to discriminate them in magnetic single-electron devices. As
a tool for further studies, we propose a simple way to determine if spin
transport or AMC effect dominates from the Coulomb blockade I-V curves of the
spintronics device
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
Spin injection in a single metallic nanoparticle: a step towards nanospintronics
We have fabricated nanometer sized magnetic tunnel junctions using a new
nanoindentation technique in order to study the transport properties of a
single metallic nanoparticle. Coulomb blockade effects show clear evidence for
single electron tunneling through a single 2.5 nm Au cluster. The observed
magnetoresistance is the signature of spin conservation during the transport
process through a non magnetic cluster.Comment: 3 page
Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet
The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode
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
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