I10-Beamline for Advanced Dichroism
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Xiaoqian
Zhang
,
Qiangsheng
Lu
,
Wenqing
Liu
,
Wei
Niu
,
Jiabao
Sun
,
Jacob
Cook
,
Mitchel
Vaninger
,
Paul F.
Miceli
,
David J.
Singh
,
Shang-Wei
Lian
,
Tay-Rong
Chang
,
Xiaoqing
He
,
Jun
Du
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Open Access
Abstract: While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 𝜇B
μ
B
/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.
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May 2021
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I10-Beamline for Advanced Dichroism
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Zhendong
Chen
,
Wenqing
Liu
,
Peng
Chen
,
Xuezhong
Ruan
,
Jiabao
Sun
,
Ruobai
Liu
,
Cunxu
Gao
,
Jun
Du
,
Bo
Liu
,
Hao
Meng
,
Rong
Zhang
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Abstract: Compensated ferrimagnetic Heusler compounds with high spin polarization and a low net magnetic moment are strategically important materials for spin-logic and further energy-efficient spintronic applications. However, the element-resolved magnetic ordering of these compensated ferrimagnets remains an open issue. Here, we report a direct observation of the spin and orbital moments of the B2 phase Mn2CoAl thin film using the synchrotron-based x-ray magnetic circular dichroism technique. An ferrimagnetic ordering between Mn and Co elements and a compensated-ferrimagnet-like small net magnetic moment of only 0.34 μB/f.u. were observed unambiguously in B2 Mn2CoAl. Antiparallel coupling between Mn and Co is attributed to the mixture of the Mn(B) and Al occupation in the B2 phase Mn2CoAl lattice. This work demonstrates great potential of the compensated ferrimagnetic half-metallic inverse Heusler compounds Mn2CoAl for spintronic applications.
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Jul 2020
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I06-Nanoscience
I10-Beamline for Advanced Dichroism
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Yu
Yan
,
Xianyang
Lu
,
Bo
Liu
,
Xiaoqian
Zhang
,
Xiangyu
Zheng
,
Hao
Meng
,
Wenqing
Liu
,
Junlin
Wang
,
Iain G.
Will
,
Jing
Wu
,
Ping Kwan Johnny
Wong
,
Jianwang
Cai
,
Jun
Du
,
Rong
Zhang
,
Yongbing
Xu
Diamond Proposal Number(s):
[16538]
Abstract: Perpendicular magnetic anisotropy (PMA) in the Ta/CoFeB/MgO system has been studied using x-ray magnetic circular dichroism and vibrating sample magnetometry. The ratios of the orbital to spin magnetic moments of Co atoms in the Ta/CoFeB/MgO structures with PMA have been found to be enhanced by 100%, compared with the Ta/CoFeB/Ta structure without PMA. The orbital moments of Co are as large as
0.30
μ
B
0.30μB
, more than half of their spin moments in the perpendicularly magnetized Ta/CoFeB/MgO structures. The results indicate that the PMA observed in the CoFeB/MgO structures is related to the increased spin–orbital coupling of the Co atoms. This work offers experimental evidence of the correlation between PMA and the element-specific spin and orbital moments in the Ta/CoFeB/MgO systems.
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Feb 2020
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[14331]
Abstract: Historically, chemists have explored chemical space in a highly uneven and unsystematic manner. As an example, the shape diversity of existing fragment sets does not generally reflect that of all theoretically possible fragments. To assess experimentally the added value of increased three dimensionality, a shape‐diverse fragment set was designed and collated. The set was assembled by both using commercially available fragments and harnessing unified synthetic approaches to sp3‐rich molecular scaffolds. The resulting set of 80 fragments was highly three‐dimensional, and its shape diversity was significantly enriched by twenty synthesised fragments. The fragment set was screened by high‐throughput protein crystallography against Aurora‐A kinase, revealing four hits that targeted the binding site of allosteric regulators. In the longer term, it is envisaged that the fragment set could be screened against a range of functionally diverse proteins, allowing the added value of more shape‐diverse screening collections to be more fully assessed.
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Apr 2019
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[20748]
Open Access
Abstract: The recently discovered topological phase offers new possibilities for spintronics and condensed matter. Even insulating material exhibits conductivity at the edges of certain systems, giving rise to an anomalous quantum Hall effect and other coherent spin transport phenomena, in which heat dissipation is minimized, with potential uses for next-generation energy-efficient electronics. While the metallic surface states of topological insulators (TIs) have been extensively studied, direct comparison of the surface and bulk magnetic properties of TIs has been little explored. We report unambiguous evidence for distinctly enhanced surface magnetism in a prototype magnetic TI, Cr-doped Bi2Se3. Using synchrotron-based x-ray techniques, we demonstrate a “three-step transition” model, with a temperature window of ~15 K, where the TI surface is magnetically ordered while the bulk is not. Understanding the dual magnetization process has strong implications for defining a physical modelof magnetic TIs and lays the foundation for applications to information technology.
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Feb 2019
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Zhonghui
Nie
,
Ion Cristian Edmond
Turcu
,
Yao
Li
,
Xiaoqian
Zhang
,
Liang
He
,
Jian
Tu
,
Zhiqiang
Ni
,
Huangfeng
Xu
,
Yequan
Chen
,
Xuezhong
Ruan
,
Fabio
Frassetto
,
Paolo
Miotti
,
Nicola
Fabris
,
Luca
Poletto
,
Jing
Wu
,
Qiangsheng
Lu
,
Chang
Liu
,
Thorsten
Kampen
,
Ya
Zhai
,
Wenqing
Liu
,
Cephise
Cacho
,
Xuefeng
Wang
,
Fengqiu
Wang
,
Yi
Shi
,
Rong
Zhang
,
Yongbing
Xu
Open Access
Abstract: A new femtosecond, Extreme Ultraviolet (EUV), Time Resolved Spin-Angle Resolved Photo-Emission Spectroscopy (TR-Spin-ARPES) beamline was developed for ultrafast materials research and development. This 50-fs laser-driven, table-top beamline is an integral part of the “Ultrafast Spintronic Materials Facility”, dedicated to engineering ultrafast materials. This facility provides a fast and in-situ analysis and development of new materials. The EUV source based on high harmonic generation process emits 2.3 × 1011 photons/second (2.3 × 108 photons/pulse) at H23 (35.7 eV) and its photon energy ranges from 10 eV to 75 eV, which enables surface sensitive studies of the electronic structure dynamics. The EUV monochromator provides the narrow bandwidth of the EUV beamline while preserving its pulse duration in an energy range of 10–100 eV. Ultrafast surface photovoltaic effect with ~650 fs rise-time was observed in p-GaAs (100) from time-resolved ARPES spectra. The data acquisition time could be reduced by over two orders of magnitude by scaling the laser driver from 1 KHz, 4W to MHz, KW average power.
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Jan 2019
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I06-Nanoscience
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Wei
Niu
,
Wenqing
Liu
,
Min
Gu
,
Yongda
Chen
,
Xiaoqian
Zhang
,
Minhao
Zhang
,
Yequan
Chen
,
Ji
Wang
,
Jun
Du
,
Fengqi
Song
,
Xiaoqing
Pan
,
Nini
Pryds
,
Xuefeng
Wang
,
Peng
Wang
,
Yongbing
Xu
,
Yunzhong
Chen
,
Rong
Zhang
Diamond Proposal Number(s):
[15239]
Abstract: Atomically engineered oxide heterostructures provide a fertile ground for creating novel states, for example, a 2D electron gas at the interface between two oxide insulators, giant thermoelectric Seebeck coefficient, emergent ferromagnetism from otherwise nonmagnetic components, and colossal ionic conductivity. Extensive research efforts reveal that oxygen deficiency or lattice strain play an important role in determining these unexpected properties. Herein, by studying the abrupt presence of robust ferromagnetism (up to 1.5 µB/Mn) in LaMnO3‐based heterostructures, the multivalence states of Mn that play a decisive role in the emergence of ferromagnetism in the otherwise antiferromagnetic LaMnO3 thin films are found. Combining spatially resolved electron energy‐loss spectroscopy, X‐ray absorption spectroscopy, and X‐ray magnetic circular dichroism techniques, it is determined unambiguously that the ferromagnetism results from a conventional Mn3+‐O‐Mn4+ double‐exchange mechanism rather than an interfacial effect. In contrast, the magnetic dead layer of 5 unit cell in proximity to the interface is found to be accompanied with the accumulation of Mn2+ induced by electronic reconstruction. These findings provide a hitherto‐unexplored multivalence state of Mn on the emergent magnetism in undoped manganite epitaxial thin films, such as LaMnO3 and BiMnO3, and shed new light on all‐oxide spintronic devices.
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Apr 2018
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[9979]
Abstract: Understanding magnetism in ferromagnetic metal/semiconductor (FM/SC) hetero-structures is important to the development of the new generation spin field-effect transistor (SpinFET). Here, we report an element-specific x-ray magnetic circularly dichroism study of the interfacial magnetic moments for two FM/SC model systems, namely Co/GaAs and Ni/GaAs, which was enabled using a specially designed FM1/FM2/SC superstructure. We observed a robust room temperature magnetization of the interfacial Co, whilst that of the interfacial Ni was strongly diminished down to 5 K due to hybridization of the Ni d(eg) and GaAs sp3 states. The validity of the selected method was confirmed by first-principles calculations, showing only small deviations (<0.02 and <0.07 μB/atom for Co/GaAs and Ni/GaAs, respectively) compared to the real FM/SC interfaces. Our work proved that the electronic structure and magnetic ground state of the interfacial FM2 is not altered when the topmost FM2 is replaced by FM1 and that this model is applicable generally for probing the buried magnetic interfaces in the advanced spintronic materials.
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Feb 2016
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I10-Beamline for Advanced Dichroism
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Wenqing
Liu
,
Damien
West
,
Liang
He
,
Yongbing
Xu
,
Jun
Liu
,
Kejie
Wang
,
Yong
Wang
,
Gerrit
Van Der Laan
,
Rong
Zhang
,
Shengbai
Zhang
,
Kang. L.
Wang
Abstract: Magnetic doping is the most common method for breaking time-reversal-symmetry surface states of topological insulators (TIs) to realize novel physical phenomena and to create beneficial technological applications. Here we present a study of the magnetic coupling of a prototype magnetic TI, that is, Cr-doped Bi2Se3, in its ultrathin limit which is expected to give rise to quantum anomalous Hall (QAH) effect. The high quality Bi2–xCrxSe3 epitaxial thin film was prepared using molecular beam epitaxy (MBE), characterized with scanning transimission electron microscopy (STEM), electrical magnetotransport, and X-ray magnetic circularly dichroism (XMCD) techniques, and the results were simulated using density functional theory (DFT) with spin–orbit coupling (SOC). We observed a sizable spin moment mspin = (2.05 ± 0.20) μB/Cr and a small and negative orbital moment morb = (−0.05 ± 0.02) μB/Cr of the Bi1.94Cr0.06Se3 thin film at 2.5 K. A remarkable fraction of the (CrBi–CrI)3+ antiferromagnetic dimer in the Bi2–xCrxSe3 for 0.02 < x < 0.40 was obtained using first-principles simulations, which was neglected in previous studies. The spontaneous coexistence of ferro- and antiferromagnetic Cr defects in Bi2–xCrxSe3 explains our experimental observations and those based on conventional magnetometry which universally report magnetic moments significantly lower than 3 μB/Cr predicted by Hund’s rule.
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Oct 2015
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