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Emergent ultra-high temperature ferromagnetism in La_(2)CoO_(4±x) thin films

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Nano Research 2024年第8期17卷 7250-7255页

作者： Ziang Meng Han Yan Peixin Qin Zhuo Yin Peiheng Jiang Xiaorong Zhou Xiaoning Wang Hongyu Chen Li Liu Zhiyuan Duan Guojian zhao weisheng zhao Fengxia Hu Qinghua Zhang Zhicheng Zhong Zhiqi Liu School of Materials Science and Engineering Beihang UniversityBeijing 100191China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China CAS Key Laboratory of Magnetic Materials and Devices and Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology Ningbo Institute of Materials Technology and EngineeringChinese Academy of SciencesNingbo 315201China Fert Beijing Institute School of Integrated Circuit Science and EngineeringBeihang UniversityBeijing 100191China

Searching for novel ferromagnetic oxides with high Curie temperature(TC)has been one of the main goals for oxide *** well-known perovskite cobaltate LaCoO_(3) is a classical ferromagnet in its thin-film form;however,it suffers from a low TC(~85 K).Here we report a new type of ferromagnetic La-Co-O films with an ultrahigh TC of~820 *** are fabricated by pulsed laser deposition from a LaCoO_(3) target at low oxygen partial *** structural analysis indicates that they crystallize in terms of the Ruddlesden–Popper phase of La_(2)CoO_(4±x).In sharp contrast to the antiferromagnetism of bulk La_(2)CoO_(4),the strong ferromagnetism in the La_(2)CoO_(4±x) thin films is firmly demonstrated by magnetometry measurements,X-ray magnetic circular dichroism characterization,and magnetotransport *** importantly,density functional theory calculations indicate that the nonstoichiometric oxygen induces an antiferromagnetic-to-ferromagnetic phase transition,accompanied by the orbital reconstruction of Co 3d ***,our study provides an attractive strategy for designing or synthesizing exotic magnetic oxides with high ordering temperatures.

关键词： ferromagnetic oxides ultra-high Curie temperature La_(2)CoO_(4) spin current transport oxygen engineering

Spin-orbit torque efficiency enhancement to tungsten-based SOT-MTJs by interface modification with an ultrathin MgO

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Science China(Information Sciences) 2024年第1期67卷 316-317页

作者： Shiyang LU Xiaobai NING Hongchao ZHANG Sixi ZHEN Xiaofei FAN Danrong XIONG Dapeng ZHU Gefei WANG Hong-Xi LIU Kaihua CAO weisheng zhao Fert Beijing Institute School of Integrated Science and EngineeringBeihang University Truth Memory Corporation

Spin-orbital torque (SOT) based three-terminal magnetic tunnel junctions (MTJs) have attracted much interest as the next generation magnetic random-access memory (MRAM)key device both in the academy and the industry. This is because SOT-MTJs feature high endurance and fast switching speed, benefiting tremendously from the separation of read/write current paths and less incubation time during the write in contrast to the spin-transfer torque (STT) MTJs [1].

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Oscillation of Dzyaloshinskii–Moriya interaction driven by weak electric fields

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Chinese Physics B 2024年第2期33卷 487-491页

作者：陈润泽曹安妮王馨苒柳洋杨洪新赵巍胜 Fert Beijing Institute MIIT Key Laboratory of SpintronicsSchool of Integrated Circuit Science and EngineeringBeihang UniversityBeijing 100191China Hefei Innovation Research Institute Beihang UniversityHefei 230013China Beihang-Goertek Joint Microelectronics Institute Qingdao Research InstituteBeihang UniversityQingdao 266000China National Laboratory of Solid State Microstructures School of PhysicsCollaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China Beijing Microelectronics Technology Institute Beijing 100076China

Dzyaloshinskii–Moriya interaction(DMI) is under extensive investigation considering its crucial status in chiral magnetic orders, such as Néel-type domain wall(DW) and skyrmions. It has been reported that the interfacial DMI originating from Rashba spin–orbit coupling(SOC) can be linearly tuned with strong external electric fields. In this work, we experimentally demonstrate that the strength of DMI exhibits rapid fluctuations, ranging from 10% to 30% of its original value, as a function of applied electric fields in Pt/Co/MgO heterostructures within the small field regime(< 10-2V/nm). Brillouin light scattering(BLS) experiments have been performed to measure DMI, and first-principles calculations show agreement with this observation, which can be explained by the variation in orbital hybridization at the Co/MgO interface in response to the weak electric fields. Our results on voltage control of DMI(VCDMI) suggest that research related to the voltage control of magnetic anisotropy for spin–orbit torque or the motion control of skyrmions might also have to consider the role of the external electric field on DMI as small voltages are generally used for the magnetoresistance detection.

关键词： Dzyaloshinskii-Moriya interaction weak electric field control effect Rashba spin-orbit coupling interfacial orbital hybridization

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存算一体芯片发展现状、趋势与挑战

中国科学：信息科学 2024年第1期54卷 16-24页

作者：康旺寇竞赵巍胜北京航空航天大学集成电路科学与工程学院北京100191

冯·诺依曼计算架构本质上面临“存储墙”和“功耗墙”瓶颈,近年来摩尔定律的放缓进一步加剧了上述瓶颈.新型存算一体芯片技术通过器件–架构–电路–工艺的协同创新,将数据存储与计算融合一体化,大幅降低数据搬运及其开销,被视为后摩... 详细信息

冯·诺依曼计算架构本质上面临“存储墙”和“功耗墙”瓶颈,近年来摩尔定律的放缓进一步加剧了上述瓶颈.新型存算一体芯片技术通过器件–架构–电路–工艺的协同创新,将数据存储与计算融合一体化,大幅降低数据搬运及其开销,被视为后摩尔时代突破冯·诺依曼架构瓶颈的重要技术方向之一.同时,存算一体芯片通过大规模并行运算方式实现高算力,在一定程度上可以缓解工艺微缩压力,对我国在新一轮人工智能革命中突破算力困境,具有重要的战略意义与应用价值.基于国家自然科学基金委员会第347期“双清论坛(青年)”,本文介绍存算一体芯片领域当前的研究现状,分析了存算一体芯片技术对我国的重要战略意义,展望了未来亟待解决的关键科学问题与技术挑战,并进一步给出了该领域的发展趋势和建议.

关键词：存内计算近存计算异构集成异构架构

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Bondage number of strong product of two paths

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Frontiers of Mathematics in China 2015年第2期10卷 435-460页

作者： weisheng zhao Heping ZHANG School of Mathematics and Statistics Lanzhou University Lanzhou 730000 China

The bondage number b（G） of a graph G is the cardinality of a minimum set of edges whose removal from G results in a graph with a domination number greater than that of G. In this paper, we obtain the exact value of the bondage number of the strong product of two paths. That is, for any two positive integers ra ≥ 2 and n ≥ 2, b（Pm × Pn） = 7 - r（m） - r（n） if （r（m）,r（n）） = （1, 1） or （3,3）, 6 - r（m） - r（n） otherwise, where r（t） is a function of positive integer t, defined as r（t） = 1 if t ≡ 1 （mod 3）, r（t） = 2 if t ≡2 （mod 3）, and r（t） = 3 if t ≡0 （mod 3）.

关键词： Bondage number strong product path

Perpendicular magnetic anisotropy based spintronics devices in Pt/Co stacks under different hard and flexible substrates

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Science China(Information Sciences) 2023年第2期66卷 256-266页

作者： Sylvain EIMER Houyi CHENG Jinji LI Xueying ZHANG Chao zhao weisheng zhao Hefei Innovation Research Institute Anhui High Reliability Chips Engineering LaboratoryBeihang University Fert Beijing Institute MIIT Key Laboratory of Spintronics School of Integrated Circuit Science and EngineeringBeihang University School of Physics and Quantum Information Research Center Southeast University Truth Instruments Co.Ltd. Beihang-Geortek Joint Microelectronics Institute Qingdao Research InstituteBeihang University Beijing Superstring Academy of Memory Technology

The magnetic properties in substrate/Pt/Co multilayers, such as perpendicular magnetic anisotropy(PMA), are of particular interest for spintronic devices. In particular, it is important to obtain a strong PMA on the flexible substrate in the field of wearable devices and structural health ***, the different stacks deposition and regulation conditions on the magnetic properties of the films lack systematic research. Here, we investigate the magnetic properties in Pt/Co structures with different hard and flexible substrates, layer thicknesses, and the different deposition temperatures of the buffer *** found that the coercive field and magnetodynamic behavior of the films change with these factors. Moreover, depositing the buffer layer under high temperature can effectively adjust the crystalline state of the films, thus affecting the performance of the films. After depositing the buffer layer at 800℃, our films can obtain a better crystalline state and PMA. The measurement results of the magneto-optical Kerr microscope show that the magnetic domain wall motion of the films can be controlled by different substrate and buffer layer conditions. It was expected that ultra-fast magnetic moment switching can be achieved by optimizing the conditions to reduce the power consumption of the device. The experimental results also show that the optimized film conditions can also obtain strong PMA on the flexible substrate. These findings help to understand magnetic properties in these structures and show the promising prospect for wearable devices and other spintronic devices.

关键词： Pt/Co stacks perpendicular magnetic anisotropy magnetodynamicbehavior spintronics flexible devices high temperature deposition

Developments and Applications of Tunneling Magnetoresistance Sensors

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Tsinghua Science and Technology 2022年第3期27卷 443-454页

作者： Shaohua Yan Zitong Zhou Yaodi Yang Qunwen Leng weisheng zhao the School of Integrated Circuit Science and Engineering Beihang UniversityBeijing 100191China Beihang-Goertek Joint Microelectronics Institute Qingdao Research Institute of Beihang UniversityQingdao 266100China

Magnetic sensors based on tunneling magnetoresistance(TMR)effect exhibit high sensitivity,small size,and low power *** have gained a lot of attention and have potential applications in various *** study first introduces the development history and basic principles of TMR ***,a comprehensive description of TMR sensors linearization and Wheatstone bridge configuration is *** key performance parameters,the field sensitivity and noise mechanisms,are ***,the emerging applications of TMR sensors are discussed.

关键词： tunneling magnetoresistance(TMR)sensor linearization Wheatstone bridge configuration noise

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Femtosecond laser-assisted switching in perpendicular magnetic tunnel junctions with double-interface free layer

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Science China(Information Sciences) 2022年第4期65卷 251-257页

作者： Luding WANG Wenlong CAI Kaihua CAO Kewen SHI Bert KOOPMANS weisheng zhao Fert Beijing Institute School of Integrated Circuit Science and Engineering Beihang University Department of Applied Physics Institute for Photonic Integration Eindhoven University of Technology

Perpendicular magnetic tunnel junctions with double-interface free layer(p-DMTJs), which exhibit enhanced tunnel magnetoresistance(TMR) and thermal stability(△) at the nanoscale, have received considerable interest as building blocks for spintronic data storage devices. Heat-assisted magnetic recording(HAMR) techniques have been widely employed in mainstream magnetic storage to enable ultrahigh storage density. However, the data access is achieved by sensing the stray field of the selected magnetic element using a mechanical “read head”, resulting in an unfavorable speed limitation and design complexity. To address this issue, integrating laser-assisted switching with a high-performance magnetic tunnel junction has received interest in spintronic R&D; however, it has not yet been achieved. In this study, we experimentally explored femtosecond(fs) laser-assisted switching in a p-DMTJ device using a direct electrical TMR readout. We demonstrate two reconfigurable switching operations, i.e., binary “write” and unidirectional “reset”, by the interplay of the fs laser and synchronized magnetic field sequence. We further explored the joint effect, and a switching phase diagram was obtained. The effect of the stray field of p-DMTJ, as well as laser helicity,on switching is also discussed. Results show the feasibility of fs laser-assisted writing p-DMTJs, which can pave the way in high-density optospintronic storage applications.

关键词： magnetic tunnel junctions (MTJs) heat-assisted magnetic recording (HAMR) spintronics femtosecond laser thermally-assisted switching (TAS)

Neuromorphic terahertz imaging based on carbon nanotube circuits

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Science China(Information Sciences) 2023年第6期66卷 303-304页

作者： Nan YANG Zhizhong SI Xinhe WANG Xiaoyang LIN weisheng zhao School of Integrated Circuit Science and Engineering Beihang University Fert Beijing Institute MIIT Key Laboratory of SpintronicsSchool of Integrated Circuit Science and EngineeringBeihang University

We propose a neuromorphic THz imaging system based on the integration of carbon nanotubes(CNTs) circuits and the spin-transfer torque magnetic tunnel junctions(STTMTJs). Utilizing the photothermoelectric effect of CNT...

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