43 research outputs found
Control of the gyration dynamics of magnetic vortices by the magnetoelastic effect
The influence of a strain-induced uniaxial magnetoelastic anisotropy on the
magnetic vortex core dynamics in microstructured magnetostrictive
CoFeB elements was investigated with time-resolved
scanning transmission x-ray microscopy. The measurements revealed a
monotonically decreasing eigenfrequency of the vortex core gyration with the
increasing magnetoelastic anisotropy, which follows closely the predictions
from micromagnetic modeling
Unexpected field-induced dynamics in magnetostrictive microstructured elements under isotropic strain
We investigated the influence of an isotropic strain on the magnetization dynamics of microstructured magnetostrictive Co40Fe40B20 (CoFeB) elements with time-resolved scanning transmission x-ray microscopy. We observed that the application of isotropic strain leads to changes in the behavior of the microstructured magnetostrictive elements that cannot be fully explained by the volume magnetostriction term. Therefore, our results prompt for an alternative explanation to the current models used for the interpretation of the influence of mechanical strain on the dynamical processes of magnetostrictive materials
Time- and spatially-resolved magnetization dynamics driven by spin-orbit torques
Current-induced spin-orbit torques (SOTs) represent one of the most effective
ways to manipulate the magnetization in spintronic devices. The orthogonal
torque-magnetization geometry, the strong damping, and the large domain wall
velocities inherent to materials with strong spin-orbit coupling make SOTs
especially appealing for fast switching applications in nonvolatile memory and
logic units. So far, however, the timescale and evolution of the magnetization
during the switching process have remained undetected. Here, we report the
direct observation of SOT-driven magnetization dynamics in Pt/Co/AlO dots
during current pulse injection. Time-resolved x-ray images with 25 nm spatial
and 100 ps temporal resolution reveal that switching is achieved within the
duration of a sub-ns current pulse by the fast nucleation of an inverted domain
at the edge of the dot and propagation of a tilted domain wall across the dot.
The nucleation point is deterministic and alternates between the four dot
quadrants depending on the sign of the magnetization, current, and external
field. Our measurements reveal how the magnetic symmetry is broken by the
concerted action of both damping-like and field-like SOT and show that
reproducible switching events can be obtained for over reversal
cycles
Time- and spatially-resolved magnetization dynamics driven by spin-orbit torques
Current-induced spin-orbit torques (SOTs) represent one of the most effective
ways to manipulate the magnetization in spintronic devices. The orthogonal
torque-magnetization geometry, the strong damping, and the large domain wall
velocities inherent to materials with strong spin-orbit coupling make SOTs
especially appealing for fast switching applications in nonvolatile memory and
logic units. So far, however, the timescale and evolution of the magnetization
during the switching process have remained undetected. Here, we report the
direct observation of SOT-driven magnetization dynamics in Pt/Co/AlO dots
during current pulse injection. Time-resolved x-ray images with 25 nm spatial
and 100 ps temporal resolution reveal that switching is achieved within the
duration of a sub-ns current pulse by the fast nucleation of an inverted domain
at the edge of the dot and propagation of a tilted domain wall across the dot.
The nucleation point is deterministic and alternates between the four dot
quadrants depending on the sign of the magnetization, current, and external
field. Our measurements reveal how the magnetic symmetry is broken by the
concerted action of both damping-like and field-like SOT and show that
reproducible switching events can be obtained for over reversal
cycles
Direct observation of N\'eel-type skyrmions and domain walls in a ferrimagnetic thin film via scanning transmission X-ray microscopy
Isolated magnetic skyrmions are stable, topologically protected spin textures
that are at the forefront of research interests today due to their potential
applications in information technology. A distinct class of skyrmion hosts are
rare earth - transition metal (RE-TM) ferrimagnetic materials. To date, the
nature and the control of basic traits of skyrmions in these materials are not
fully understood. We show that for an archetypal ferrimagnetic material that
exhibits strong perpendicular anisotropy, the ferrimagnetic skyrmion size can
be tuned by external magnetic fields. Moreover, by taking advantage of the high
spatial resolution of scanning transmission X-ray microscopy (STXM) and
utilizing a large x-ray magnetic linear dichroism (XMLD) contrast that occurs
naturally at the RE resonant edges, we resolve the nature of the magnetic
domain walls of ferrimagnetic skyrmions. We demonstrate that through this
method one can easily discriminate between Bloch and N\'eel type domain walls
for each individual skyrmion. For all isolated ferrimagnetic skyrmions, we
observe that the domain walls are of N\'eel-type. This key information is
corroborated with results of micromagnetic simulations and allows us to
conclude on the nature of the Dzyaloshinskii-Moriya interaction (DMI) which
concurs to the stabilisation of skyrmions in ferrimagnetic systems.
Establishing that an intrinsic DMI occurs in RE-TM materials will also be
beneficial towards a deeper understanding of chiral spin texture control in
ferrimagnetic materials
Quantifying the spin-wave asymmetry in single and double rectangular NiFe microstrips by TR-STXM, FMR and micromagnetic simulations
The asymmetry of spin-wave patterns in confined rectangular
NiFe microstrips, both in single and double-strip geometries, is
quantified. The results of TR-STXM and micromagnetic simulations are compared.
For the TR-STXM measurements and the corresponding simulations the excitation
was a uniform microwave field with a fixed frequency of 9.43 GHz, while the
external static magnetic field was swept. In the easy axis orientation of the
analyzed microstrip, the results show a higher asymmetry for the double
microstrip design, indicating an influence of the additional microstrip placed
in close proximity to the analyzed one
Observation of the out-of-plane magnetization in a mesoscopic ferromagnetic structure superjacent to a superconductor
The geometry of magnetic flux penetration in a high temperature superconductor at a buried interface was imaged using element-specific x-ray excited luminescence. We performed low temperature observation of the flux penetration in YBa2Cu3O7–δ (YBCO) at a buried interface by imaging of the perpendicular magnetization component in square Permalloy (Py) mesostructures patterned superjacent to a YBCO film. Element specific imaging below the critical temperature of YBCO reveals a cross-like geometry of the perpendicular magnetization component which is decorated by regions of alternating out-of-plane magnetization at the edges of the patterned Py structures. The cross structure can be attributed to the geometry of flux penetration originating from the superconductor and is reproduced using micromagnetic simulations. Our experimental method opens up possibilities for the investigation of flux penetration in superconductors at the nanoscale