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Chinese Physics Letters 2024年第4期41卷 132-138页

作者：朱蒙董建艇李新录郑凡星周晔吴琨张佳 School of Physics and Wuhan National High Magnetic Field Center Huazhong University of Science and TechnologyWuhan 430074China

In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust against external magnetic field,etc.However,unlike ferromagnetic orders,which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions,the antiferromagnetic order(i.e.,Néel vector)cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets.Recently discovered spin-splitting noncollinear antiferromagnets,such as Mn_(3)Pt with momentum-dependent spin polarization due to their special magnetic space group,make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions.Through first-principles calculations,we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn_(3)Pt/perovskite oxides/Mn_(3)Pt antiferromagnetic tunnel junctions.We also reveal the switching dynamics of Mn_(3)Pt thin film under magnetic fields using atomistic spin dynamic simulation.Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.

关键词： tunneling magnetoresistance momentum

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

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Chinese Physics B 2024年第3期33卷 602-608页

作者：何雄杨凡黎牛浩峪王立峰易立志许云丽刘敏潘礼庆夏正才 Hubei Engineering Research Center of Weak Magnetic-field Detection College of ScienceChina Three Gorges UniversityYichang 443002China Wuhan National High Magnetic Field Center Huazhong University of Science and TechnologyWuhan 430074China

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance(MR)effect in a low static magnetic field environment at room temperature.However,how to obtain a large room-temperature negative MR effect in them remains to be studied.In this paper,by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side,we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment,but not in a static low magnetic field environment.Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory,we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field.This theoretical analytical model is further confirmed by regulating the geometry size of the device.Our work sheds light on the development of novel magnetic sensing,magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

关键词： magnetoresistance germanium-based devices pulsed high magnetic fields

Negative magnetoresistance in the antiferromagnetic semimetal V_(1/3)TaS_(2)

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Chinese Physics B 2024年第3期33卷 567-571页

作者：王子彭馨张胜男苏亚慧赖少东周旋吴春翔周霆宇王杭栋杨金虎陈斌翟会飞吴泉生杜建华焦志伟方明虎 Department of Physics China Jiliang UniversityHangzhou 310018China Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of SciencesBeijing 100190China Department of Physics Zhejiang UniversityHangzhou 310027China Department of Physics Hangzhou Normal UniversityHangzhou 310036China University of Chinese Academy of Sciences Beijing 100049China Collaborative Innovation Center of Advanced Microstructure Nanjing 210093China

Intercalated transition metal dichalcogenides(TMDCs)attract much attention due to their rich properties and potential applications.In this article,we grew successfully high-quality V_(1/3)TaS_(2) crystals by a vapor transport method.We measured the magnetization,longitudinal resistivityρxx(T,H),Hall resistivityρxy(T,H),as well as performed calculations of the electronic band structure.It was found that V_(1/3)TaS_(2) is an A-type antiferromagnet with the Neel temperature T_(N)=6.20 K,and exhibits a negative magnetoresistance(MR)near T_(N).Both band structure calculations and Hall resistivity measurements demonstrated it is a magnetic semimetal.

关键词： magnetoresistance antiferromagnetic semimetal band structure

Defect-manipulated magnetoresistance and above-room-temperature ferromagnetism in two-dimensional BaNi_(2)V_(2)O_(8)

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Chinese Chemical Letters 2024年第3期35卷 523-527页

作者： Pengfei Tan Chuanhui Zhu Jinjin Yang Shuang Zhao Tao Xia Mei-Huan Zhao Tao Han Zheng Deng Man-Rong Li Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education School of ChemistrySun Yat-sen UniversityGuangzhou 510006China School of Science and Engineering The Chinese University of Hong KongShenzhen 518172China Institute of Physics Chinese Academy of SciencesBeijing 100190China School of Science Hainan UniversityHaikou 570228China

The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.

关键词： Layered honeycomb oxide Topochemical reduction Oxygen vacancies Ferromagnetism magnetoresistance

magnetoresistance retraction behaviour of Ag/p-Ge:Ga/Ag device under pulsed high magnetic field

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Journal of Materials Science & Technology 2022年第19期114卷 1-6页

作者： Xiong He Zhengcai Xia Haoyu Niu Zhuo Zeng Wuhan National High Magnetic Field Center Huazhong University of Science and TechnologyWuhan 430074China School of Physics Huazhong University of Science and TechnologyWuhan 430074China

In non-magnetic semiconductor materials,unsaturated magnetoresistance(MR)effect has attracted lots of attention due to its physical interests and potential applications in electronic devices.Under the ex-tremely high magnetic field,the stability and reliability of MR effects based on the non-ohmic transport has been rarely researched.In this paper,the transport properties of non-magnetic Ag/p-Ge:Ga/Ag devices under 45 T pulsed high magnetic field at 300 K are investigated.It is found that in ohmic conduction re-gion(I<5 mA)where the single dominant carrier is hole,the MR values increase with increasing the applied magnetic field,presenting a conventional unsaturated behavior.In the two non-ohmic regions(5 mA≤I≤100 mA)where the transport is dominated by bipolar(electrons and holes),a MR retraction has been obviously observed under pulsed high magnetic field.Combining the Hall measurement results and calculation of Hall effect with bipolar-driven transport model,the mechanism of the MR retraction is analysed,in which the MR retraction may be related to the strong regulation of electron-to-hole den-sity ratio by pulsed high magnetic field.This work provides a reference for evaluating the stability and reliability of the properties of non-magnetic semiconductor based MR devices under the interference of strong magnetic pulses.

关键词： Germanium-based device magnetoresistance Bipolar transport Retraction behavior Pulsed high magnetic field

magnetoresistance anomaly in Fe_(5)GeTe_(2)homo-junctions induced by its intrinsic transition

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Nano Research 2023年第7期16卷 10443-10450页

作者： Ruijie Zhao Yanfei Wu Shaohua Yan Xinjie Liu He Huang Yang Gao Mengyuan Zhu Jianxin Shen Shipeng Shen Weifeng Xu Zeyu Zhang Liyuan Zhang Jingyan Zhang Xinqi Zheng Hechang Lei Ying Zhang Shouguo Wang School of Materials Science and Engineering Beijing Advanced Innovation Center for Materials Genome EngineeringUniversity of Science and Technology BeijingBeijing 100083China Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials&Micro-nano Devices Renmin University of ChinaBeijing 100872China School of Materials Science and Engineering Anhui UniversityHefei 230601China Institute of Advanced Materials Beijing Normal UniversityBeijing 100875China Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of SciencesBeijing 100190China

Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices,and exploring various physical phenomena or technologies.Among them,Fe_(5)GeTe_(2)(F5GT)has ferromagnetic order close to room temperature,however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored.Here,we systematically demonstrate the peculiar magnetic properties of Fe_(5)GeTe_(2)nanoflakes near its intrinsic transition temperature(Tp)which is far lower than its Curie temperature(TC)of~265 K,and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements.The strongest anomalous Hall effect occurs around Tp which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses.Furthermore,negative magnetoresistance(N-MR)and butterfly-shaped magnetoresistance(B-MR)are observed in F5GT homo-junction devices,and they appeared only in an intermediate temperature range from 110 to 160 K,noticeably showing the maxima near the T_(p)rather than the lowest temperature.Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices,which imply a new strategy to achieve highperformance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.

关键词： Two-dimensional(2D)van der Waals magnets Fe_(5)GeTe_(2) homo-junction magnetoresistance

Probing the magnetization switching with in-plane magnetic anisotropy through field-modified magnetoresistance measurement

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Chinese Physics B 2022年第1期31卷 101-106页

作者：郝润润张昆李迎港曹强张学莹朱大鹏赵巍胜 Fert Beijing Institute MIIT Key Laboratory of SpintronicsSchool of Integrated Circuit Science and EngineeringBeihang UniversityBeijing 100191China Beihang-Goertek Joint Microelectronics Institute Qingdao Research InstituteBeihang UniversityQingdao 266000China Spintronics Institute University of JinanJinan 250022China Truth Instruments Co.Ltd. Qingdao 266000Chin

Effective probing current-induced magnetization switching is highly required in the study of emerging spin-orbit torque(SOT)effect.However,the measurement of in-plane magnetization switching typically relies on the giant/tunneling magnetoresistance measurement in a spin valve structure calling for complicated fabrication process,or the non-electric approach of Kerr imaging technique.Here,we present a reliable and convenient method to electrically probe the SOT-induced in-plane magnetization switching in a simple Hall bar device through analyzing the MR signal modified by a magnetic field.In this case,the symmetry of MR is broken,resulting in a resistance difference for opposite magnetization orientations.Moreover,the feasibility of our method is widely evidenced in heavy metal/ferromagnet(Pt/Ni_(20)Fe_(80) and W/Co_(20)Fe_(60)B_(20))and the topological insulator/ferromagnet(Bi_(2)Se_(3)/Ni_(20)Fe_(80)).Our work simplifies the characterization process of the in-plane magnetization switching,which can promote the development of SOT-based devices.

关键词： magnetoresistance in-plane magnetization switching electrical detection

基于室温铁磁性的(Fe,Al)共掺杂SiGe铁磁pn二极管的可调整流和磁阻特性

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Science China Materials 2024年第2期67卷 573-579页

作者：李加飞张析向钢 College of Physics Sichuan UniversityChengdu 610064China

Ⅳ族稀磁半导体因其优异的磁电性能,以及在与当前主流半导体集成技术兼容的自旋电子器件中具有广阔的应用前景而受到越来越多的关注.事实上,具有室温铁磁性的Ⅳ族稀磁半导体及其衍生器件更有望在实际中得以应用.本工作设计并制备了基于p... 详细信息

Ⅳ族稀磁半导体因其优异的磁电性能,以及在与当前主流半导体集成技术兼容的自旋电子器件中具有广阔的应用前景而受到越来越多的关注.事实上,具有室温铁磁性的Ⅳ族稀磁半导体及其衍生器件更有望在实际中得以应用.本工作设计并制备了基于p型(Fe,Al)共掺杂SiGe薄膜和n型Ge衬底的磁性pn二极管.磁性测量以及磁阻和反常霍尔效应测试揭示了p型(Fe,Al)共掺杂SiGe薄膜的室温铁磁性.有趣的是,磁性pn异质结表现出磁场可调的整流和磁阻行为.我们的研究结果为制备具有室温铁磁性的Ⅳ族稀磁半导体提供了一种可选策略,并为Ⅳ族稀磁半导体的实际自旋电子应用提供了范例.

关键词： diluted magnetic semiconductor SiGe pn junction rectification magnetoresistance

magnetoresistance in the ferromagnet/insulator/ferromagnet tunnel junction

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Chinese Physics B 2008年第2期17卷 680-684页

作者：陆红霞董正超付浩 Department of Physics Huaiyin Teacher College

Recently experiments and theories show that the tunnel magnetoresistance （TMR） does not only depend on the ferromagnetic metal electrodes but also on the insulator. Considering the rough-scattering effect and spin-flip effect in the insulator, this paper investigates the TMR ratio in a ferromagnet/insulator/ferromagnet （FM/I/FM） tunnelling junction by using Slonczewsik＇s model. A more general expression of TMR ratio as a function of barrier height, interface roughness and spin-flip effect is obtained. In lower barrier case, it shows that the TMR ratio depends on the roughscattering effect and spin-flip effect.

关键词： magnetoresistance spin-flip effect rough-scattering

magnetoresistance and exchange bias in high Mn content melt-spun Mn_(46)Ni_(42)Sn_(11)Sb_1 alloy ribbon

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Chinese Physics B 2016年第5期25卷 316-320页

作者：黄庆学陈峰华张敏刚许小红 Heavy Machinery Engineering Research Center of Education Ministry College of Mechanical EngineeringTaiyuan University of Science and Technology School of Chemistry and Materials Science Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education Shanxi Normal University

Highly textured Heusler alloy Mn_（46）Ni_（42）Sn_（11）Sb_1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic transformation（MT）, and magnetoresistance（MR） properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 k Oe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias（EB） effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon.

关键词： Heusler alloy melt spun magnetoresistance exchange bias