7 research outputs found
Nanoscale Skyrmions in a Nonchiral Metallic Multiferroic: Ni<sub>2</sub>MnGa
Magnetic
skyrmions belong to a set of topologically nontrivial spin textures
at the nanoscale that have received increased attention due to their
emergent behavior and novel potential spintronic applications. Discovering
materials systems that can host skyrmions at room temperature in the
absence of external magnetic field is of crucial importance not only
from a fundamental aspect, but also from a technological point of
view. So far, the observations of skyrmions in bulk metallic ferromagnets
have been limited to low temperatures and to materials that exhibit
strong chiral interactions. Here we show the formation of nanoscale
skyrmions in a nonchiral multiferroic material, which is ferromagnetic
and ferroelastic, Ni<sub>2</sub>MnGa at room temperature without the
presence of external magnetic fields. By using Lorentz transmission
electron microscopy in combination with micromagnetic simulations,
we elucidate their formation, behavior, and stability under applied
magnetic fields at room temperature. The formation of skyrmions in
a multiferroic material with no broken inversion symmetry presents
new exciting opportunities for the exploration of the fundamental
physics of topologically nontrivial spin textures
Visualization of the Magnetic Structure of Sculpted Three-Dimensional Cobalt Nanospirals
In this work, we report on the direct
visualization of magnetic
structure in sculpted three-dimensional cobalt (Co) nanospirals with
a wire diameter of 20 nm and outer spiral diameter of 115 nm and on
the magnetic interactions between the nanospirals, using aberration-corrected
Lorentz transmission electron microscopy. By analyzing the magnetic
domains in three dimensions at the nanoscale, we show that magnetic
domain formation in the Co nanospirals is a result of the shape anisotropy
dominating over the magnetocrystalline anisotropy of the system. We
also show that the strong dipolar magnetic interactions between adjacent
closely packed nanospirals leads to their magnetization directions
adopting alternating directions to minimize the total magnetostatic
energy of the system. Deviations from such magnetization structure
can only be explained by analyzing the complex three-dimensional structure
of the nanospirals. These nanostructures possess an inherent chirality
due to their growth conditions and are of significant importance as
nanoscale building blocks in magneto-optical devices
Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices
The physics of phase transitions in two-dimensional (2D)
systems
underpins research in diverse fields including statistical mechanics,
nanomagnetism, and soft condensed matter. However, many aspects of
2D phase transitions are still not well understood, including the
effects of interparticle potential, polydispersity, and particle shape.
Magnetic skyrmions are chiral spin-structure quasi-particles that
form two-dimensional lattices. Here, we show, by real-space imaging
using in situ cryo-Lorentz transmission electron
microscopy coupled with machine learning image analysis, the ordering
behavior of NeĢel skyrmion lattices in van der Waals Fe3GeTe2. We demonstrate a distinct change in the
skyrmion size distribution during field-cooling, which leads to a
loss of lattice order and an evolution of the skyrmion liquid phase.
Remarkably, the lattice order is restored during field heating and
demonstrates a thermal hysteresis. This behavior is explained by the
skyrmion energy landscape and demonstrates the potential to control
the lattice order in 2D phase transitions
Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices
The physics of phase transitions in two-dimensional (2D)
systems
underpins research in diverse fields including statistical mechanics,
nanomagnetism, and soft condensed matter. However, many aspects of
2D phase transitions are still not well understood, including the
effects of interparticle potential, polydispersity, and particle shape.
Magnetic skyrmions are chiral spin-structure quasi-particles that
form two-dimensional lattices. Here, we show, by real-space imaging
using in situ cryo-Lorentz transmission electron
microscopy coupled with machine learning image analysis, the ordering
behavior of NeĢel skyrmion lattices in van der Waals Fe3GeTe2. We demonstrate a distinct change in the
skyrmion size distribution during field-cooling, which leads to a
loss of lattice order and an evolution of the skyrmion liquid phase.
Remarkably, the lattice order is restored during field heating and
demonstrates a thermal hysteresis. This behavior is explained by the
skyrmion energy landscape and demonstrates the potential to control
the lattice order in 2D phase transitions
Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices
The physics of phase transitions in two-dimensional (2D)
systems
underpins research in diverse fields including statistical mechanics,
nanomagnetism, and soft condensed matter. However, many aspects of
2D phase transitions are still not well understood, including the
effects of interparticle potential, polydispersity, and particle shape.
Magnetic skyrmions are chiral spin-structure quasi-particles that
form two-dimensional lattices. Here, we show, by real-space imaging
using in situ cryo-Lorentz transmission electron
microscopy coupled with machine learning image analysis, the ordering
behavior of NeĢel skyrmion lattices in van der Waals Fe3GeTe2. We demonstrate a distinct change in the
skyrmion size distribution during field-cooling, which leads to a
loss of lattice order and an evolution of the skyrmion liquid phase.
Remarkably, the lattice order is restored during field heating and
demonstrates a thermal hysteresis. This behavior is explained by the
skyrmion energy landscape and demonstrates the potential to control
the lattice order in 2D phase transitions
Enhancement of Local Piezoresponse in Polymer Ferroelectrics <i>via</i> 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 Ī²-phase extended chain crystals <i>via</i> 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
Xāray Irradiation Induced Reversible Resistance Change in Pt/TiO<sub>2</sub>/Pt Cells
The interaction between X-rays and matter is an intriguing topic for both fundamental science and possible applications. In particular, synchrotron-based brilliant X-ray beams have been used as a powerful diagnostic tool to unveil nanoscale phenomena in functional materials. However, it has not been widely investigated how functional materials respond to the brilliant X-rays. Here, we report the X-ray-induced reversible resistance change in 40-nm-thick TiO<sub>2</sub> films sandwiched by Pt top and bottom electrodes, and propose the physical mechanism behind the emergent phenomenon. Our findings indicate that there exists a photovoltaic-like effect, which modulates the resistance reversibly by a few orders of magnitude, depending on the intensity of impinging X-rays. We found that this effect, combined with the X-ray irradiation induced phase transition confirmed by transmission electron microscopy, triggers a nonvolatile reversible resistance change. Understanding X-ray-controlled reversible resistance changes can provide possibilities to control initial resistance states of functional materials, which could be useful for future information and energy storage devices