I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[26148]
Open Access
Abstract: A major challenge in topological magnetism lies in the three-dimensional (3D) exploration of their magnetic textures. A recent focus has been the question of how 2D skyrmion sheets vertically stack to form distinct types of 3D topological strings. Being able to manipulate the vertical coupling should therefore provide a route to the engineering of topological states. Here, we present a new type of axially bound magnetic skyrmion string state in which the strings in two distinct materials are glued together across their interface. With quasi-tomographic resonant elastic X-ray scattering, the 3D skyrmion profiles before and after their binding across the interface were unambiguously determined and compared. Their attractive binding is accompanied by repulsive twisting; i.e., the coupled skyrmions mutually affect each other via a compensating twisting. This state exists in chiral magnet–magnetic thin film heterostructures, providing a new arena for the engineering of 3D topological phases.
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Apr 2022
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I10-Beamline for Advanced Dichroism
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Yao
Guang
,
Kejing
Ran
,
Junwei
Zhang
,
Yizhou
Liu
,
Senfu
Zhang
,
Xuepeng
Qiu
,
Yong
Peng
,
Xixiang
Zhang
,
Markus
Weigand
,
Joachim
Gräfe
,
Gisela
Schütz
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Shilei
Zhang
,
Guoqiang
Yu
,
Xiufeng
Han
Diamond Proposal Number(s):
[23785]
Abstract: A three-dimensional singular point that consists of two oppositely aligned emergent monopoles is identified in continuous CoTb thin films, as confirmed by complementary techniques of resonant elastic x-ray scattering, Lorentz transmission electron microscopy, and scanning transmission x-ray microscopy. This new type of topological defect can be regarded as a superposition of an emergent magnetic monopole and an antimonopole, around which the source and drain of the magnetic flux overlap in space. We experimentally prove that the observed spin twist seen in Lorentz transmission electron microscopy reveals the cross section of the superimposed three-dimensional structure, providing a straightforward strategy for the observation of magnetic singularities. Such a quasiparticle provides an excellent platform for studying the rich physics of emergent electromagnetism.
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Nov 2021
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[20182]
Open Access
Abstract: A chiral bobber is a localized three-dimensional magnetization configuration, terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in chiral magnets, lending themselves to new types of skyrmion-complementary bits of information. However, the on-demand creation of bobbers, as well as their direct observation remained elusive. Here, we introduce a new mechanism for creating a stable chiral bobber lattice state via the proximity of two skyrmion species with comparable size. This effect is experimentally demonstrated in a
Cu
2
OSeO
3
/
[
Ta
/
CoFeB
/
MgO
]
4
heterostructure in which an exotic bobber lattice state emerges in the phase diagram of
Cu
2
OSeO
3
. To unambiguously reveal the existence of the chiral bobber lattice state, we have developed a novel characterization technique, magnetic truncation rod analysis, which is based on resonant elastic x-ray scattering.
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Jan 2021
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I10-Beamline for Advanced Dichroism
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Yao
Guang
,
Yong
Peng
,
Zhengren
Yan
,
Yizhou
Liu
,
Junwei
Zhang
,
Xue
Zeng
,
Senfu
Zhang
,
Shilei
Zhang
,
David M.
Burn
,
Nicolas
Jaouen
,
Jinwu
Wei
,
Hongjun
Xu
,
Jiafeng
Feng
,
Chi
Fang
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Baoshan
Cui
,
Xixiang
Zhang
,
Guoqiang
Yu
,
Xiufeng
Han
Diamond Proposal Number(s):
[20183, 21868]
Abstract: The emergence of magnetic skyrmions, topological spin textures, has aroused tremendous interest in studying the rich physics related to their topology. While skyrmions promise high‐density and energy‐efficient magnetic memory devices for information technology, the manifestation of their nontrivial topology through single skyrmions and ordered and disordered skyrmion lattices could also give rise to many fascinating physical phenomena, such as chiral magnon and skyrmion glass states. Therefore, generating skyrmions at designated locations on a large scale, while controlling the skyrmion patterns, is the key to advancing topological magnetism. Here, a new, yet general, approach to the “printing” of skyrmions with zero‐field stability in arbitrary patterns on a massive scale in exchange‐biased magnetic multilayers is presented. By exploiting the fact that the antiferromagnetic order can be reconfigured by local thermal excitations, a focused electron beam with a graphic pattern generator to “print” skyrmions is used, which is referred to as skyrmion lithography. This work provides a route to design arbitrary skyrmion patterns, thereby establishing the foundation for further exploration of topological magnetism.
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Aug 2020
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I10-Beamline for Advanced Dichroism
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Peng
Chen
,
Yong
Zhang
,
Qi
Yao
,
Fugu
Tian
,
Lun
Li
,
Zhengkun
Qi
,
Xiaoyang
Liu
,
Liyang
Liao
,
Cheng
Song
,
Jingyuan
Wang
,
Jing
Xia
,
Gang
Li
,
David M.
Burn
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Shilei
Zhang
,
Xufeng
Kou
Diamond Proposal Number(s):
[21875, 23895]
Abstract: Engineering the anomalous Hall effect (AHE) is the key to manipulate the magnetic orders in the emerging magnetic topological insulators (MTIs). In this letter, we synthesize the epitaxial Bi2Te3/MnTe magnetic heterostructures and observe pronounced AHE signals from both layers combined together. The evolution of the resulting hybrid AHE intensity with the top Bi2Te3 layer thickness manifests the presence of an intrinsic ferromagnetic phase induced by the topological surface states at the heterolayer interface. More importantly, by doping the Bi2Te3 layer with Sb, we are able to manipulate the sign of the Berry phase-associated AHE component. Our results demonstrate the unparalleled advantages of MTI heterostructures over magnetically doped TI counterparts in which the tunability of the AHE response can be greatly enhanced. This in turn unveils a new avenue for MTI heterostructure-based multifunctional applications.
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Feb 2020
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[17612]
Open Access
Abstract: Magnetic skyrmions are two-dimensional magnetization swirls that stack in the form of tubes in the third dimension and which are proposed as prospective information carriers for nonvolatile memory devices due to their unique topological properties. From resonant elastic X-ray scattering measurements on Cu2OSeO3 with an in-plane magnetic field, we find that a state of perpendicularly ordered skyrmions forms, in stark contrast to the well-studied bulk state. The surface state is stable over a wide temperature range, unlike the bulk state in out-of-plane fields which is confined to a narrow region of the temperature-field phase diagram. In contrast to ordinary skyrmions found in the bulk, the surface state skyrmions result from the presence of magnetic interactions unique to the surface which stabilize them against external perturbations. The surface guiding makes the robust state particular interesting for racetracklike devices, ultimately allowing for much higher storage densities due to the smaller lateral footprint of the perpendicular skyrmions.
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Jan 2020
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[20182, 20437]
Abstract: Magnetic skyrmions are nanosized magnetization whirls that exhibit topological robustness and nontrivial magnetoelectrical properties, such as emergent electromagnetism and intriguing spin dynamics in the microwave-frequency region. In chiral magnets, skyrmions are usually found at a pocket in the phase diagram in the vicinity of the ordering temperature, wherein they order in the form of a hexagonal skyrmion lattice (SkL). It is generally believed that this equilibrium SkL phase is a uniform, long-range-ordered magnetic structure with a well-defined lattice constant. Here, using high-resolution small-angle resonant elastic x-ray scattering, we study the field and temperature dependence of the skyrmion lattice in FeGe and
Cu
2
OSeO
3
membranes. Indeed,
Cu
2
OSeO
3
shows the expected rigid skyrmion lattice, known from bulk samples, that is unaffected by tuning field and temperature within the phase pocket. In stark contrast, the lattice constant and skyrmion size in FeGe membranes undergo a continuous evolution within the skyrmion phase pocket, whereby the lattice constant changes by up to 15% and the magnetic scattering intensity varies significantly. Using micromagnetic modeling, it is found that for FeGe the competing energy terms contributing to the formation of the skyrmion lattice fully explain this breathing behavior. In contrast, for
Cu
2
OSeO
3
this stabilizing energy balance is less affected by the smaller field variation across the skyrmion pocket, leading to the observed rigid lattice structure.
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Jan 2020
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I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[18898]
Open Access
Abstract: Collective spin excitations of ordered magnetic structures offer great potential for the development of novel spintronic devices. The present approach relies on micromagnetic models to explain the origins of dynamic modes observed by ferromagnetic resonance (FMR) studies, since experimental tools to directly reveal the origins of the complex dynamic behavior are lacking. Here we demonstrate a new approach which combines resonant magnetic X-ray diffraction with FMR, thereby allowing for a reconstruction of the real-space spin dynamics of the system. This new diffractive FMR technique builds on X-ray detected FMR that allows for element-selective dynamic studies, giving unique access to specific wave components of static and dynamic coupling in magnetic heterostructures. In combination with diffraction, FMR is elevated to the level of a modal spectroscopy technique, potentially opening new pathways for the development of spintronic devices.
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Dec 2019
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Xiyang
Li
,
Shilei
Zhang
,
Hang
Li
,
Diego
Alba Venero
,
Jonathan S
White
,
Robert
Cubitt
,
Qingzhen
Huang
,
Jie
Chen
,
Lunhua
He
,
Gerrit
Van Der Laan
,
Wenhong
Wang
,
Thorsten
Hesjedal
,
Fangwei
Wang
Open Access
Abstract: A biskyrmion consists of two bound, topologically stable, skyrmion spin textures. These coffee‐bean‐shaped objects are observed in real space in thin plates using Lorentz transmission electron microscopy (LTEM). From LTEM imaging alone, it is not clear whether biskyrmions are surface‐confined objects, or, analogous to skyrmions in non-centrosymmetric helimagnets, 3D tube‐like structures in a bulk sample. Here, the biskyrmion form factor is investigated in single‐ and polycrystalline‐MnNiGa samples using small‐angle neutron scattering. It is found that biskyrmions are not long‐range ordered, not even in single crystals. Surprisingly all of the disordered biskyrmions have their in‐plane symmetry axis aligned along certain directions, governed by the magneto-crystalline anisotropy. This anisotropic nature of biskyrmions may be further exploited to encode information.
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Mar 2019
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I10-Beamline for Advanced Dichroism
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Wenjing
Li
,
Iuliia
Bykova
,
Shilei
Zhang
,
Guoqiang
Yu
,
Riccardo
Tomasello
,
Mario
Carpentieri
,
Yizhou
Liu
,
Yao
Guang
,
Joachim
Gräfe
,
Markus
Weigand
,
David M.
Burn
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Zhengren
Yan
,
Jiafeng
Feng
,
Caihua
Wan
,
Jinwu
Wei
,
Xiao
Wang
,
Xiaomin
Zhang
,
Hongjun
Xu
,
Chenyang
Guo
,
Hongxiang
Wei
,
Giovanni
Finocchio
,
Xiufeng
Han
,
Gisela
Schütz
Diamond Proposal Number(s):
[18898]
Open Access
Abstract: Room temperature magnetic skyrmions in magnetic multilayers are considered as information carriers for future spintronic applications. Currently, a detailed understanding of the skyrmion stabilization mechanisms is still lacking in these systems. To gain more insight, it is first and foremost essential to determine the full real-space spin configuration. Here, two advanced X-ray techniques are applied, based on magnetic circular dichroism, to investigate the spin textures of skyrmions in [Ta/CoFeB/MgO]n multilayers. First, by using ptychography, a high-resolution diffraction imaging technique, the 2D out-of-plane spin profile of skyrmions with a spatial resolution of 10 nm is determined. Second, by performing circular dichroism in resonant elastic X-ray scattering, it is demonstrated that the chirality of the magnetic structure undergoes a depthdependent evolution. This suggests that the skyrmion structure is a complex 3D structure rather than an identical planar texture throughout the layer stack. The analyses of the spin textures confirm the theoretical predictions that the dipole–dipole interactions together with the external magnetic field play an important role in stabilizing sub-100 nm diameter skyrmions and the hybrid structure of the skyrmion domain wall. Our combined X-ray-based approach opens the door for in-depth studies of magnetic skyrmion systems, which allows for precise engineering of optimized skyrmion heterostructures.
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Feb 2019
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