scholarly journals Real-space observations of 60-nm skyrmion dynamics in an insulating magnet under low heat flow

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiuzhen Yu ◽  
Fumitaka Kagawa ◽  
Shinichiro Seki ◽  
Masashi Kubota ◽  
Jan Masell ◽  
...  
Keyword(s):  
Heat Flow ◽  
Domain Walls ◽  
Spin Dynamics ◽  
Real Space ◽  
Fundamental Physics ◽  
Ferromagnetic Domain ◽  
Comparable Magnitude ◽  
Widespread Interest ◽  
Space Observations

AbstractThermal-current induced electron and spin dynamics in solids –dubbed “caloritronics”– have generated widespread interest in both fundamental physics and spintronics applications. Here, we examine the dynamics of nanometric topological spin textures, skyrmions driven by a temperature gradient ∇T or heat flow, that are evaluated through in-situ real-space observations in an insulating helimagnet Cu2OSeO3. We observe increases of the skyrmion velocity and the Hall angle with increasing ∇T above a critical value of ~ 13 mK/mm, which is two orders of magnitude lower than the ∇T required to drive ferromagnetic domain walls. A comparable magnitude of ∇T is also observed to move the domain walls between a skyrmion domain and the non-topological conical-spin domain from cold to hot regions. Our results demonstrate the efficient manipulation of skyrmions by temperature gradients, a promising step towards energy-efficient “green” spintronics.

scholarly journals Real-space observations of 60-nm skyrmion dynamics in an insulating magnet under low heat flow

2021 ◽  
Author(s):  
Xiuzhen Yu ◽  
Fumitaka Kagawa ◽  
Shinichiro Seki ◽  
Masashi Kubota ◽  
Jan Masell ◽  
...  
Keyword(s):  
Heat Flow ◽  
Domain Walls ◽  
Spin Dynamics ◽  
Real Space ◽  
Fundamental Physics ◽  
Theoretical Predictions ◽  
Comparable Magnitude ◽  
Widespread Interest ◽  
Space Observations

Abstract Thermal-current induced electron and spin dynamics in solids –dubbed “caloritronics” – have generated widespread interest in both fundamental physics and spintronics applications. Here, we examine the dynamics of nanometric topological spin textures, skyrmions, driven by a temperature gradient or heat flow. The heat-flow-drive skyrmion dynamics are evaluated through in-situ real-space observations in an insulating helimagnet Cu2OSeO3. We observe increases of the skyrmion velocity and the Hall angle with increasing T above a critical value of ~ 13 mK/mm, which is two orders of magnitude lower than the T required to drive ferromagnetic domain walls, in agreement with theoretical predictions. A comparable magnitude of T is also observed to move the domain walls between a skyrmion domain and the non-topological conical-spin domain from cold to hot regions. Our results demonstrate the efficient manipulation of skyrmions by temperature gradients, a promising step towards energy-efficient “green” spintronics.

scholarly journals In-situ twistable bilayer graphene

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Cheng Hu ◽  
Tongyao Wu ◽  
Xinyue Huang ◽  
Yulong Dong ◽  
Jiajun Chen ◽  
...  
Keyword(s):  
Domain Walls ◽  
Near Field ◽  
Twist Angle ◽  
Bilayer Graphene ◽  
Real Space ◽  
Systematic Investigation ◽  
Force Microscopy ◽  
Atomic Force ◽  
Resonant Raman

AbstractThe electrical and optical properties of twisted bilayer graphene (tBLG) depend sensitively on the twist angle. To study the angle dependent properties of the tBLG, currently it is required fabrication of a large number of samples with systematically varied twist angles. Here, we demonstrate the construction of in-situ twistable bilayer graphene, in which the twist angle of the two graphene monolayers can be in-situ tuned continuously in a large range with high precision. The controlled tuning of the twist angle is confirmed by a combination of real-space and spectroscopic characterizations, including atomic force microscopy (AFM) identification of crystal lattice orientation, scanning near-field optical microscopy (SNOM) imaging of superlattice domain walls, and resonant Raman spectroscopy of the largely enhanced G-mode. The developed in-situ twistable homostructure devices enable systematic investigation of the twist angle effects in a single device, thus could largely advance the research of twistronics.

scholarly journals Magnetisation Processes in Geometrically Frustrated Spin Networks with Self-Assembled Cliques

Entropy ◽  
2020 ◽  
Vol 22 (3) ◽  
pp. 336 ◽  
Author(s):  
Bosiljka Tadić ◽  
Miroslav Andjelković ◽  
Milovan Šuvakov ◽  
Geoff J. Rodgers
Keyword(s):  
Domain Walls ◽  
Spin Dynamics ◽  
Higher Order ◽  
Spin Networks ◽  
Graph Theoretic ◽  
Geometrically Frustrated ◽  
Geometric Frustration ◽  
Antiferromagnetic Materials ◽  
Geometrically Constrained ◽  
Ferromagnetic Interactions

Functional designs of nanostructured materials seek to exploit the potential of complex morphologies and disorder. In this context, the spin dynamics in disordered antiferromagnetic materials present a significant challenge due to induced geometric frustration. Here we analyse the processes of magnetisation reversal driven by an external field in generalised spin networks with higher-order connectivity and antiferromagnetic defects. Using the model in (Tadić et al. Arxiv:1912.02433), we grow nanonetworks with geometrically constrained self-assemblies of simplexes (cliques) of a given size n, and with probability p each simplex possesses a defect edge affecting its binding, leading to a tree-like pattern of defects. The Ising spins are attached to vertices and have ferromagnetic interactions, while antiferromagnetic couplings apply between pairs of spins along each defect edge. Thus, a defect edge induces n − 2 frustrated triangles per n-clique participating in a larger-scale complex. We determine several topological, entropic, and graph-theoretic measures to characterise the structures of these assemblies. Further, we show how the sizes of simplexes building the aggregates with a given pattern of defects affects the magnetisation curves, the length of the domain walls and the shape of the hysteresis loop. The hysteresis shows a sequence of plateaus of fractional magnetisation and multiscale fluctuations in the passage between them. For fully antiferromagnetic interactions, the loop splits into two parts only in mono-disperse assemblies of cliques consisting of an odd number of vertices n. At the same time, remnant magnetisation occurs when n is even, and in poly-disperse assemblies of cliques in the range n ∈ [ 2 , 10 ] . These results shed light on spin dynamics in complex nanomagnetic assemblies in which geometric frustration arises in the interplay of higher-order connectivity and antiferromagnetic interactions.

scholarly journals Imaging the Polymorphic Transformation in a Single Cu6Sn5 Grain in a Solder Joint

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2229 ◽  
Author(s):  
Flora Somidin ◽  
Hiroshi Maeno ◽  
Xuan Tran ◽  
Stuart D. McDonald ◽  
Mohd Mohd Salleh ◽  
...  
Keyword(s):  
Solder Joint ◽  
Polymorphic Transformation ◽  
Structural Evolution ◽  
Real Space ◽  
Transformation Behavior ◽  
New Approach ◽  
Transmission Electron ◽  
Contrast Pattern ◽  
In Situ Observations

In-situ observations of the polymorphic transformation in a single targeted Cu6Sn5 grain constrained between Sn-0.7 wt % Cu solder and Cu-Cu3Sn phases and the associated structural evolution during a solid-state thermal cycle were achieved via a high-voltage transmission electron microscope (HV-TEM) technique. Here, we show that the monoclinic η′-Cu6Sn5 superlattice reflections appear in the hexagonal η-Cu6Sn5 diffraction pattern upon cooling to isothermal 140 °C from 210 °C. The in-situ real space imaging shows that the η′-Cu6Sn5 contrast pattern is initiated at the grain boundary. This method demonstrates a new approach for further understanding the polymorphic transformation behavior on a real solder joint.

scholarly journals Flux Mapping and Magnetic Behavior of Grain Boundaries in Nd-Fe-B Magnets

1999 ◽  
Vol 589 ◽  
Author(s):  
V.V. Volkov ◽  
Yimei Zhu
Keyword(s):  
Magnetic Flux ◽  
Grain Boundaries ◽  
Domain Walls ◽  
Quantitative Description ◽  
Magnetic Behavior ◽  
Local Variation ◽  
Smooth Transition ◽  
Lorentz Microscopy ◽  
Hard Magnets

AbstractAdvanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.

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