33 research outputs found
Understanding the effect of curvature on the magnetization reversal of three-dimensional nanohelices
Comprehending the interaction between geometry and magnetism in
three-dimensional (3D) nanostructures is of importance to understand the
fundamental physics of domain wall (DW) formation and pinning. Here, we use
focused electron beam-induced deposition to fabricate magnetic nanohelices with
increasing helical curvature with height. Using electron tomography and Lorentz
transmission electron microscopy, we reconstruct the 3D structure and
magnetization of the nanohelices. The surface curvature, helical curvature and
torsion of the nanohelices are then quantified from the tomographic
reconstructions. Furthermore, by using the experimental 3D reconstructions as
inputs for micromagnetic simulations we can reveal the influence of surface and
helical curvature on the magnetic reversal mechanism. Hence, we can directly
correlate the magnetic behavior of a 3D nanohelix to its experimental
structure. These results demonstrate how control of geometry in nanohelices can
be utilized in the stabilization of DWs and control of the response of the
nanostructure to applied magnetic fields
Nanosecond electron imaging of transient electric fields and material response
Electrical pulse stimulation drives many important physical phenomena in
condensed matter as well as in electronic systems and devices. Often,
nanoscopic and mesoscopic mechanisms are hypothesized, but methods to image
electrically driven dynamics on both their native length and time scales have
so far been largely undeveloped. Here, we present an ultrafast electron
microscopy approach that uses electrical pulses to induce dynamics and records
both the local time-resolved electric field and corresponding material behavior
with nanometer-nanosecond spatiotemporal resolution. Quantitative measurement
of the time-dependent field via the electron beam deflection is demonstrated by
recording the field between two electrodes with single-ns temporal resolution.
We then show that this can be applied in a material by correlating applied
field with resulting dynamics in TaS. First, time-resolved electron
diffraction is used to simultaneously record the electric field and crystal
structure change in a selected region during a 20 ns voltage pulse, showing how
a charge density wave transition evolves during and after the applied field.
Then, time-resolved nanoimaging is demonstrated, revealing heterogeneous
distortions that occur in the freestanding flake during a longer, lower
amplitude pulse. Altogether, these results pave the way for future experiments
that will uncover the nanoscale dynamics underlying electrically driven
phenomena.Comment: Main article: 7 pages, 3 figures. Supplemental Material: 8 pages, 7
figure
3D reconstruction of magnetization from dichroic soft X-ray transmission tomography
The development of magnetic nanostructures for applications in spintronics requires methods capable of visualizing their magnetization. Soft Xâray magnetic imaging combined with circular magnetic dichroism allows nanostructures up to 100â300â
nm in thickness to be probed with resolutions of 20â40â
nm. Here a new iterative tomographic reconstruction method to extract the threeâdimensional magnetization configuration from tomographic projections is presented. The vector field is reconstructed by using a modified algebraic reconstruction approach based on solving a set of linear equations in an iterative manner. The application of this method is illustrated with two examples (magnetic nanoâdisc and microâsquare heterostructure) along with comparison of error in reconstructions, and convergence of the algorithm
Enhancement of Local Piezoresponse in Polymer Ferroelectrics via Nanoscale Control of Microstructure
Polymer ferroelectrics are flexible and lightweight electromechanical materials that are widely studied due to their potential application as sensors, actuators, and energy harvesters. However, one of the biggest challenges is their low piezoelectric coefficient. Here, we report a mechanical annealing effect based on local pressure induced by a nanoscale tip that enhances the local piezoresponse. This process can control the nanoscale material properties over a microscale area at room temperature. We attribute this improvement to the formation and growth of ÎČ-phase extended chain crystals via sliding diffusion and crystal alignment along the scan axis under high mechanical stress. We believe that this technique can be useful for local enhancement of piezoresponse in ferroelectric polymer thin films
Coexistence of Merons with Skyrmions in the Centrosymmetric van der Waals Ferromagnet Fe5GeTe2
FeGeTe is a centrosymmetric, layered van der Waals (vdW)
ferromagnet that displays Curie temperatures (270-330 K) that are within
the useful range for spintronic applications. However, little is known about
the interplay between its topological spin textures (e.g., merons, skyrmions)
with technologically relevant transport properties such as the topological Hall
effect (THE), or topological thermal transport. Here, we show via
high-resolution Lorentz transmission electron microscopy that merons and
anti-meron pairs coexist with N\'{e}el skyrmions in FeGeTe over a
wide range of temperatures and probe their effects on thermal and electrical
transport. We detect a THE, even at room , that senses merons at higher s
as well as their coexistence with skyrmions as is lowered indicating an
on-demand thermally driven formation of either type of spin texture.
Remarkably, we also observe an unconventional THE in absence of Lorentz force
and attribute it to the interaction between charge carriers and magnetic
field-induced chiral spin textures. Our results expose FeGeTe as a
promising candidate for the development of applications in skyrmionics/meronics
due to the interplay between distinct but coexisting topological magnetic
textures and unconventional transport of charge/heat carriers.Comment: In press. Four figures in the main text. Includes SI file with 19
additional figure
Three Dimensional Visualization of Electromagnetic Fields from One Dimensional Nanostructures
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