I10-Beamline for Advanced Dichroism
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Xiaoqian
Zhang
,
Wenqing
Liu
,
Wei
Niu
,
Qiangsheng
Lu
,
Wei
Wang
,
Ali
Sarikhani
,
Xiaohua
Wu
,
Chunhui
Zhu
,
Jiabao
Sun
,
Mitchel
Vaninger
,
Paul. F.
Miceli
,
Jianqi
Li
,
David J.
Singh
,
Yew San
Hor
,
Yue
Zhao
,
Chang
Liu
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Dapeng
Yu
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Abstract: One of the most promising avenues in 2D materials research is the synthesis of antiferromagnets employing 2D van der Waals (vdW) magnets. However, it has proven challenging, due in part to the complicated fabrication process and undesired adsorbates as well as the significantly deteriorated ferromagnetism at atomic layers. Here, the engineering of the antiferromagnetic (AFM) interlayer exchange coupling between atomically thin yet ferromagnetic CrTe2 layers in an ultra-high vacuum-free 2D magnetic crystal, Cr5Te8 is reported. By self-introducing interstitial Cr atoms in the vdW gaps, the emergent AFM ordering and the resultant giant magnetoresistance effect are induced. A large negative magnetoresistance (10%) with a plateau-like feature is revealed, which is consistent with the AFM interlayer coupling between the adjacent CrTe2 main layers in a temperature window of 30 K below the Néel temperature. Notably, the AFM state has a relatively weak interlayer exchange coupling, allowing a switching between the interlayer AFM and ferromagnetic states at moderate magnetic fields. This work represents a new route to engineering low-power devices that underpin the emerging spintronic technologies, and an ideal laboratory to study 2D magnetism.
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May 2022
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[16538]
Open Access
Abstract: As an emerging class of two-dimensional (2D) materials, van der Waals (vdW) magnets have attracted a lot of research attention since they can give access to fundamental physics and potential spintronic device applications. Among these 2D vdW magnets, CrSiTe3, as an intrinsic ferromagnetic semiconductor, exhibits great potentials in low-dimensional spintronics. Of particular interest in this 2D vdW magnet is the electronic and magnetic properties at the atomic-scale, which has yet been fully explored so far. Here, combing angle-resolved photoemission spectroscopy, bulk magnetic measurements, and synchrotron-based x-ray techniques, an unambiguous picture of the electronic and magnetic states of CrSiTe3 is presented. Hybridization of Cr-3d and Te-5p orbitals and the semiconducting behavior are confirmed by the band structure detection. Intrinsic ferromagnetism with a magnetic anisotropy constant of 1.56 × 105 erg/cm3 is attributed to the superexchange interaction of the Cr3+ ions. In addition, temperature-dependent spin and orbital moments are determined, and a fitted critical exponent of 0.169 implies that CrSiTe3 is in good agreement with the 2D Ising model. More remarkably, unquenched orbital moments are experimentally evidenced, bringing CrSiTe3 with orbital-dependent intriguing effects and great potentials toward the spintronic devices.
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Oct 2021
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I10-Beamline for Advanced Dichroism
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Shanshan
Liu
,
Zihan
Li
,
Ke
Yang
,
Enze
Zhang
,
Awadhesh
Narayan
,
Xiaoqian
Zhang
,
Jiayi
Zhu
,
Wenqing
Liu
,
Zhiming
Liao
,
Masaki
Kudo
,
Takaaki
Toriyama
,
Yunkun
Yang
,
Qiang
Li
,
Linfeng
Ai
,
Ce
Huang
,
Jiabao
Sun
,
Xiaojiao
Guo
,
Wenzhong
Bao
,
Qingsong
Deng
,
Yanhui
Chen
,
Lifeng
Yin
,
Jian
Shen
,
Xiaodong
Han
,
Syo
Matsumura
,
Jin
Zou
,
Yongbing
Xu
,
Xiaodong
Xu
,
Hua
Wu
,
Faxian
Xiu
Diamond Proposal Number(s):
[20748]
Open Access
Abstract: Two-dimensional (2D) ferromagnetic materials have been discovered with tunable magnetism and orbital-driven nodal-line features. Controlling the 2D magnetism in exfoliated nanoflakes via electric/magnetic fields enables the boosted Curie temperature (TC) or phase transitions. One of the challenges, however, is the realization of high TC 2D magnets that are tunable, robust and suitable for large scale fabrication. Here, we report molecular-beam epitaxy growth of wafer-scale Fe3+XGeTe2 films with TC above-room-temperature. By controlling the Fe composition in Fe3+XGeTe2, a continuously-modulated TC in a broad range of 185–320 K has been achieved. This widely tunable TC is attributed to the doped interlayer Fe that provide a 40% enhancement around the optimal composition X = 2. We further fabricated magnetic tunneling junction device arrays that exhibit clear tunneling signals. Our results show an effective and reliable approach, i.e. element doping, to produce robust and tunable ferromagnetism beyond room temperature in a large-scale 2D Fe3+XGeTe2 fashion.
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Jul 2021
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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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Diamond Proposal Number(s):
[20748]
Abstract: Over the past four years, the magnetism of 2D magnets has been extensively studied by the full arsenal of probing techniques. 2D magnets can be incorporated to form heterostructures with clean and sharp interfaces, which gives rise to exotic phenomena as a result of the interfacial proximity effect. Here we report a detailed study of the spin (ms) and orbital (ml) moments of an epitaxial (CrSb/Fe3GeTe2)6 superlattice. The synchrotron-radiation based x-ray magnetic circular dichroism (XMCD) technique was performed to probe the microscopic magnetic properties of the superlattices in an elemental resolved manner. We unambiguously obtained a bulk-like moment of Fe3GeTe2 i.e., ms = 1.58 ± 0.2 μB/Fe and ml = 0.22 ± 0.02 μB/Fe. Future works to explore the tuning of the spin polarized band structure of 2D ferromagnetic superlattices will be of great interest and can have strong implications for both fundamental physics and the emerging spintronics technology.
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May 2021
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I10-Beamline for Advanced Dichroism
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Wei
Niu
,
Yue‐wen
Fang
,
Xiaoqian
Zhang
,
Yakui
Weng
,
Yongda
Chen
,
Hui
Zhang
,
Yulin
Gan
,
Xiao
Yuan
,
Shengjie
Zhang
,
Jiabao
Sun
,
Yile
Wang
,
Lujun
Wei
,
Yongbing
Xu
,
Xuefeng
Wang
,
Wenqing
Liu
,
Yong
Pu
Diamond Proposal Number(s):
[20748]
Abstract: Transition‐metal oxide (TMO) heterostructures provide fertile grounds for creating and manipulating intriguing properties and functionalities. At the interface of TMO heterostructures, electronic reconstructions generally occur via charge transfer and lead to an extraordinary spectrum of emergent phenomena but unattainable in their bulk constituents. However, the basic mechanism of charge transfer at the interface is not fully determined or even understood in heterostructures, which may hide the underlying mechanisms and intriguing physics. Herein, an intrinsic charge transfer and resultant exotic ferromagnetism are unambiguously observed in the heterostructures between the nonmagnetic LaCoO3 (LCO) and SrTiO3 (STO). Combining element‐specific X‐ray absorption spectroscopy and atomic multiplet fitting, direct evidence of charge transfer‐induced multivalence of cobalt ions, interactions of which would contribute to the novel magnetism beyond the intuition, in concert with first‐principles density‐functional‐theory calculations, is demonstrated. Beyond LCO/STO system, a more broadly applicable principle for the heterostructures between 3d TMO and STO where charge transfer and resultant multivalence or conducting interfaces are coexistent is establish. This study represents an advance that the electronic reconstruction and the multiple electron configurations of 3d transition metal ions will constitute a powerful tool for the designs of functional materials and creations of unconventional physical properties.
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Nov 2020
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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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I10-Beamline for Advanced Dichroism
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Shanshan
Liu
,
Ke
Yang
,
Wenqing
Liu
,
Enze
Zhang
,
Zihan
Li
,
Xiaoqian
Zhang
,
Zhiming
Liao
,
Wen
Zhang
,
Jiabao
Sun
,
Yunkun
Yang
,
Han
Gao
,
Ce
Huang
,
Linfeng
Ai
,
Ping Kwan Johnny
Wong
,
Andrew Thye Shen
Wee
,
Alpha T
N’diaye
,
Simon A.
Morton
,
Xufeng
Kou
,
Jin
Zou
,
Yongbing
Xu
,
Hua
Wu
,
Faxian
Xiu
Diamond Proposal Number(s):
[20748]
Open Access
Abstract: Mechanically-exfoliated two-dimensional ferromagnetic materials (2D FMs) were discovered to possess long-range ferromagnetic order and topologically nontrivial skyrmions in few-layers. However, owing to the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature (TC) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their TC, particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-TC 2D FM Fe3GeTe2 (FGT) via A-type antiferromagnetic material CrSb (CS) which strongly couples to FGT. A superlattice structure of (FGT/CS)n, where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing the elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally discovered that TC of 4-layer Fe3GeTe2 can be significantly enhanced from 140 K to 230 K because of the interfacial ferromagnetic coupling. In the meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic CrSb into a ferrimagnetic state as evidenced by a double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the TC enhancement of the Fe3GeTe2 films, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in 4-layer FGT/CS superlattice, TC can be further enhanced to near room temperature. Our results provide a feasible approach in enhancing the magnetic order of few-layer 2D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices.
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Dec 2019
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