52 research outputs found
Controlled anisotropic dynamics of tightly bound skyrmions in a synthetic ferrimagnet due to skyrmion-deformation mediated by induced uniaxial in-plane anisotropy
We study speed and skew deflection-angle dependence on skyrmion deformations
of a tightly bound two-skyrmion state in a synthetic ferrimagnet. We condsider
here, an in-plane uniaxial magnetocrystalline anisotropy-term in order to
induce lateral shape distortions and an overall size modulation of the
skyrmions due to a reduction of the effective out-of-plane anisotropy, thus
affecting the skyrmion speed, skew-deflection and inducing anisotropy in these
quantities with respect to the driving current-angle. Because of frustrated
dipolar interactions in a synthetic ferrimagnet, sizeable skyrmion deformations
can be induced with relatively small induced anisotropy constants and thus a
wide range of tuneability can be achieved. We also show analytically, that a
consequence of the skyrmion deformation can, under certain conditions cause a
skyrmion deflection with respect to driving-current angles, unrelated to the
topological charge. Results are analyzed by a combination of micromagnetic
simulations and a compound particle description within the Thiele-formalism
from which an over-all mobility tensor is constructed. This work offers an
additional path towards in-situ tuning of skyrmion dynamics
Dynamics and inertia of skyrmionic spin structures
Skyrmions are topologically protected winding vector fields characterized by a spherical topology. Magnetic skyrmions can arise as the result of the interplay of various interactions, including exchange, dipolar and anisotropy energy in the case of magnetic bubbles and an additional Dzyaloshinskii-Moriya interaction in the case of chiral skyrmions. Whereas the static and low-frequency dynamics of skyrmions are already well under control, their gigahertz dynamical behaviour has not been directly observed in real space. Here, we image the gigahertz gyrotropic eigenmode dynamics of a single magnetic bubble and use its trajectory to experimentally confirm its skyrmion topology. The particular trajectory points to the presence of strong inertia, with a mass much larger than predicted by existing theories. This mass is endowed by the topological confinement of the skyrmion and the energy associated with its size change. It is thereby expected to be found in all skyrmionic structures in magnetic systems and beyond. Our experiments demonstrate that the mass term plays a key role in describing skyrmion dynamics.
Room temperature chiral magnetic skyrmion in ultrathin magnetic nanostructures
Magnetic skyrmions are chiral spin structures with a whirling configuration.
Their topological properties, nanometer size and the fact that they can be
moved by small current densities have opened a new paradigm for the
manipulation of magnetisation at the nanoscale. To date, chiral skyrmion
structures have been experimentally demonstrated only in bulk materials and in
epitaxial ultrathin films and under external magnetic field or at low
temperature. Here, we report on the observation of stable skyrmions in
sputtered ultrathin Pt/Co/MgO nanostructures, at room temperature and zero
applied magnetic field. We use high lateral resolution X-ray magnetic circular
dichroism microscopy to image their chiral N\'eel internal structure which we
explain as due to the large strength of the Dzyaloshinskii-Moriya interaction
as revealed by spin wave spectroscopy measurements. Our results are
substantiated by micromagnetic simulations and numerical models, which allow
the identification of the physical mechanisms governing the size and stability
of the skyrmions.Comment: Submitted version. Extended version to appear in Nature
Nanotechnolog
Inertia-driven resonant excitation of a magnetic skyrmion
Topological spin structures such as magnetic domain walls, vortices, and skyrmions, have been receiving great interest because of their high potential application in various spintronic devices. To utilize them in the future spintronic devices, it is first necessary to understand the dynamics of the topological spin structures. Since inertial effect plays a crucial role in the dynamics of a particle, understanding the inertial effect of topological spin structures is an important task. Here, we report that a strong inertial effect appears steadily when a skyrmion is driven by an oscillating spin-Hall-spintorque (SHST). We find that the skyrmion exhibits an inertia-driven hypocycloid-type trajectory when it is excited by the oscillating SHST. This motion has not been achieved by an oscillating magnetic field, which only excites the breathing mode without the inertial effect. The distinct inertial effect can be explained in terms of a spin wave excitation in the skyrmion boundary which is induced by the non-uniform SHST. Furthermore, the inertia-driven resonant excitation provides a way of experimentally estimating the inertial mass of the skyrmion. Our results therefore pave the way for the development of skyrmion-based device applications
Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy
Magnetic skyrmions are topologically protected spin textures with attractive properties suitable for high-density and low-power spintronic device applications. Much effort has been dedicated to understanding the dynamical behaviours of the magnetic skyrmions. However, experimental observation of the ultrafast dynamics of this chiral magnetic texture in real space, which is the hallmark of its quasiparticle nature, has so far remained elusive. Here, we report nanosecond-dynamics of a 100nm-diameter magnetic skyrmion during a current pulse application, using a time-resolved pump-probe soft X-ray imaging technique. We demonstrate that distinct dynamic excitation states of magnetic skyrmions, triggered by current-induced spin-orbit torques, can be reliably tuned by changing the magnitude of spin-orbit torques. Our findings show that the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque on the nanosecond time scale, which points to exciting opportunities for ultrafast and novel skyrmionic applications in the future.clos
Safety of intravenous ferric carboxymaltose versus oral iron in patients with nondialysis-dependent CKD: an analysis of the 1-year FIND-CKD trial.
Background: The evidence base regarding the safety of intravenous (IV) iron therapy in patients with chronic kidney disease (CKD) is incomplete and largely based on small studies of relatively short duration. Methods: FIND-CKD (ClinicalTrials.gov number NCT00994318) was a 1-year, open-label, multicenter, prospective study of patients with nondialysis-dependent CKD, anemia and iron deficiency randomized (1:1:2) to IV ferric carboxymaltose (FCM), targeting higher (400-600 µg/L) or lower (100-200 µg/L) ferritin, or oral iron. A post hoc analysis of adverse event rates per 100 patient-years was performed to assess the safety of FCM versus oral iron over an extended period. Results: The safety population included 616 patients. The incidence of one or more adverse events was 91.0, 100.0 and 105.0 per 100 patient-years in the high ferritin FCM, low ferritin FCM and oral iron groups, respectively. The incidence of adverse events with a suspected relation to study drug was 15.9, 17.8 and 36.7 per 100 patient-years in the three groups; for serious adverse events, the incidence was 28.2, 27.9 and 24.3 per 100 patient-years. The incidence of cardiac disorders and infections was similar between groups. At least one ferritin level ≥800 µg/L occurred in 26.6% of high ferritin FCM patients, with no associated increase in adverse events. No patient with ferritin ≥800 µg/L discontinued the study drug due to adverse events. Estimated glomerular filtration rate remained the stable in all groups. Conclusions: These results further support the conclusion that correction of iron deficiency anemia with IV FCM is safe in patients with nondialysis-dependent CKD
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