Magnetoresistance hysteresis in the superconducting state of kagome CsV_(3)Sb_(5)

The hysteresis of magnetoresistance observed in superconductors is of great interest due to its potential connectionwith unconventional superconductivity.In this study,we perform electrical transport measurements on kagome superconductorCsV_(3)Sb_(5)nanoflakes and uncover unusual hysteretic behavior of magnetoresistance in the superconducting state.This hysteresis can be induced by applying either a large DC or AC current at temperatures(T)well below the superconductingtransition temperature(T_(c)).As T approaches T_(c),similar weak hysteresis is also detected by applying a smallcurrent.Various scenarios are discussed,with particular focus on the effects of vortex pinning and the presence of timereversal-symmtery-breaking superconducting domains.Our findings support the latter,hinting at chiral superconductivityin kagome superconductors.

Linear magnetoresistance and structural distortion in layered SrCu_(4-x)P_(2) single crystals

We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.

Magnetic Switching Dynamics and Tunnel Magnetoresistance Effect Based on Spin-Splitting Noncollinear Antiferromagnet Mn_(3)Pt

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.

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

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.

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

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.

Colossal negative magnetoresistance in spin glass Na(Zn,Mn)Sb

We report the study of magnetic and transport properties of polycrystalline and single crystal Na(Zn,Mn)Sb,a new member of“111”type of diluted magnetic materials.The material crystallizes into Cu2Sb-type structure which is isostructural to“111”type Fe-based superconductors.With suitable carrier and spin doping,the Na(Zn,Mn)Sb establishes spin-glass ordering with freezing temperature(Tf)below 15 K.Despite lack of long-range ferromagnetic ordering,Na(Zn,Mn)Sb single crystal still shows sizeable anomalous Hall effect below Tf.Carrier concentration determined by Hall effect measurements is over 1019 cm-3.More significantly,we observe colossal negative magnetoresistance(MR≡[ρ(H)−ρ(0)]/ρ(0))of-94%in the single crystal sample.

Nonmonotonic anomalous Hall effect and anisotropic magnetoresistance in SrRuO_(3)/PbZr_(0.52)Ti_(0.48)O_(3)heterostructures

We fabricate SrRuO_(3)/PbZr_(0.52)Ti_(0.48)O_(3)heterostructures each with an in-plane tensile-strained SrRuO_(3)layer and investigate the effect of an applied electric field on anomalous Hall effect.The four-fold symmetry of anisotropic magnetoresistance and the nonmonotonic variation of anomalous Hall resistivity are observed.By applying positive electric field or negative electric field,the intersecting hump-like feature is suppressed or enhanced,respectively.The sign and magnitude of the anomalous Hall conductivity can be effectively controlled with an electric field under a high magnetic field.The electric-field-modulated anomalous Hall effect is associated with the magnetization rotation in SrRuO_(3).The experimental results are helpful in modulating the magnetization rotation in spintronic devices based on SrRuO_(3)heterostructures.

Negative magnetoresistance in Dirac semimetal Cd_(3)As_(2)with in-plane magnetic field perpendicular to current

Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.

Measurement of T wave in magnetocardiography using tunnel magnetoresistance sensor

Several critical clinical applications of magnetocardiography(MCG)involve its T wave.The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic.Tunnel magnetoresistance(TMR)attracts attention as a new MCG measurement technique.However,the T waves measured by TMR are often drowned in noise.The accuracy of T waves needs to be discussed to determine the clinical value of MCG measured by TMR.This study uses an improved empirical mode decomposition(EMD)algorithm and averaging to eliminate the noise in the MCG measured by TMR.The MCG signals measured by TMR are compared with MCG measured by the optically pumped magnetometer(OPM)to judge its accuracy.Using the MCG measured by OPM as a reference,the relative errors in time and amplitude of the T wave measured by TMR are 3.4%and 1.8%,respectively.This is the first demonstration that TMR can accurately measure the time and amplitude of MCG T waves.The ability to provide reliable T wave data illustrates the significant clinical application value of TMR in MCG measurement.

Electric modulation of anisotropic magnetoresistance in Pt/HfO_(2-x)/NiO_(y)/Ni heterojunctions

Electric field control of magnetism through nanoionics has attracted tremendous attention owing to its high efficiency and low power consumption.In solid-state dielectrics,an electric field drives the redistribution of ions to create onedimensional magnetic conductive nanostructures,enabling the realization of intriguing magnetoresistance(MR)effects.Here,we explored the electric-controlled nickel and oxygen ion migration in Pt/HfO_(2-x)/NiO_(y)/Ni heterojunctions for MR modulation.By adjusting the voltage polarity and amplitude,the magnetic conductive filaments with mixed nickel and oxygen vacancy are constructed.This results in the reduction of device resistance by~10^(3)folds,and leads to an intriguing partial asymmetric MR effect.We show that the difference of the device resistance under positive and negative saturation magnetic fields exhibits good linear dependence on the magnetic field angle,which can be used for magnetic field direction detection.Our study suggests the potential of electrically controlled ion migration in creating novel magnetic nanostructures for sensor applications.

Abnormal magnetoresistance effect in the Nb/Si superconductor–semiconductor heterojunction

Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor–semiconductor heterojunctions have been fabricated by electron beam lithography and reactive ion etching.An abnormal magnetoresistance effect,which manifests itself as a zero field resistance peak under a magnetic field applied perpendicular to the interface,has been distinctly observed when the Nb film is in the superconductiing state.By considering the heterojunction interface being equivalent to the structure of superconductor–barrier layer–superconductor configuration,we could generally understand this unusual effect based on the Andreev reflection mechanism.Our results can be of help for the future development on compatibility and scalability of the silicon-based nanoscale superconducting devices for integrated circuits and superconducting quantum electronics.

Spin Hall Magnetoresistance in Pt/BiFeO_(3)Bilayer

Multiferroic materials are general antiferromagnets with negligibly small net magnetization,which strongly limits their magnetoelectric applications in spintronics.Spin Hall magnetoresistance(SMR)is sensitive to the orientation of the Néel vector,which can be applied for the detection of antiferromagnetic states.Here,we apply SMR on the unique room-temperature antiferromagnetic multiferroic material BiFeO_(3)(BFO).The angular dependence of SMR in a bilayer of epitaxial BFO(001)and heavy metal Pt is studied.By rotating the sample under a magnetic field of 80 kOe in the film plane,the resistance shows the maximum when the field is perpendicular to the current while it shows the minimum when the field is along the current.This can be well explained by the SMR in the bilayer of heavy metal/antiferromagnet with the relative orientation between the Néel vector and current direction.In contrast,the angular dependence of the resistance of Pt directly deposited on a SrTiO_(3)(001)substrate shows a 90°shift with the magnetic field rotating in the film plane,which originates from the Hanle magnetoresistance of Pt.The obtained spin mixing conductance at the Pt/BFO interface clearly confirms the efficient spin transmission.Our results provide a possible solution for applications of antiferromagnetic multiferroic materials in spintronics.

基于环形均匀磁场的磨粒传感器设计

针对传统的电感式磨粒传感器流量较小、监测区域磁感应强度较低、梯度较大的问题,设计了一种基于环形均匀磁场的磨粒传感器。通过设计环形流道,实现在监测区域内产生均匀径向磁场。同时分析了磁路截面面积与传感器磁感应强度的关系,并比较不同磁极截面形状对磁感应强度的影响,完成了对传感器的结构优化,得出采用楔形磁极可有效提高磁场利用率。利用Ansys软件建立传感器的三维有限元模型,揭示了传感器的静磁场和瞬态特性。利用单磨粒无油液实验,对比分析实验结果与仿真结构的输出特性,验证了传感器的有效性。实验结果表明,传感器在采用低倍率放大器的情况下,可检测出0.28 mm的铁磁性磨粒,与现有的传感器相比具有较高的灵敏度。

磁传感器检测磁性纳米粒子方法研究

磁性纳米粒子表面修饰后,可以与核酸、蛋白质、重金属离子等物质结合,通过检测磁粒子的磁响应信号,可以得到待测物的含量。基于电磁学理论与隧道磁阻效应,设计了一种用于检测不同质量磁性纳米粒子磁信号的测试平台。利用COMSOL Multiphysics有限元分析软件优化了磁场产生装置,改进后的线圈在通入直流电流不变的情况下,能将磁场的均匀区域扩大1.5倍,数值提高2 Gs。新型三匝线圈的实验结果与仿真结果相比最大误差为6.25%。选择了适合常规样品的磁场检测装置,分析了各类传感器的最优测量方向,测得了磁粒子质量与输出信号的关系曲线。实验结果表明:随着悬浮液中磁粒子含量的增加,隧道磁阻(TMR)传感器的输出信号也呈上升趋势,两者为线性正比关系。

电力系统宽频宽动态电流量测技术研究综述

新型电力系统要求电流互感器具备宽频带、宽量程、高准确度性能,以满足电网呈现出的时频域宽动态、多参量等新特征。因此,从磁场传感的机理出发,对电流测量传感耦合原理简要介绍,分别阐述了这些技术的优缺点、拓扑结构。重点讨论了各类电流传感装置的结构特点、性能参数及量测性能优化方案,最后总结了目前亟待解决的问题、发展趋势和应用前景。光学电流互感器技术日趋成熟,应用广泛。基于NV色心的磁传感技术在测量性能方面已经超过传统传感器,配合光纤传感技术环境适应性强,电流测量领域前景广阔。

子午工程二期宽频地磁波监测仪研制

地球的磁层中存在各种波现象,其频率从mHz延伸到数千Hz.这些波的研究一直是空间物理学研究的核心问题.针对目前世界上地磁台站的波监测设备均为各自测量相对变化、缺乏统一标定、无法进行从高纬到低纬联合观测、无法进行多台设备观测数据的统一对比研究的现状,本文综合使用磁阻传感器(探测ULF频段:1 mHz~2 Hz)、巨磁感抗传感器(探测ELF频段:0.2 Hz~2 kHz)和线圈传感器(探测VLF频段:0.2 kHz~10 kHz)研制新一代的宽频地磁波监测仪,将这些监测仪放置在120°E子午链附近的黑龙江漠河站(高纬)、北京十三陵站(中纬)、海南乐东站(低纬)等典型区域的地磁台站上,并对各个台站的设备进行统一的时间、振幅和频率标定,结合FY-3E、SMILE等近地空间卫星数据,全面提升对地球磁层的各种波现象的探测能力.研制的宽频地磁波监测仪的性能测试实验表明,其具有对一定频率(1 mHz~10 kHz)的波的探测能力;其幅度探测范围为:±65000 nT(ULF频段)、±1000 nT(ELF频段)、±100 pT(VLF频段);在量程范围内又具有较低的非线性误差:ULF频段≤0.0446%、ELF频段≤0.51%、VLF频段≤1.18%;噪声水平也较低:RMS(方均根)噪声≤0.5554 nT(ULF频段)、NPS(功率谱)噪声≤0.028 nT/√Hz(ELF频段)、NPS(功率谱)噪声≤0.24 pT/√Hz(VLF频段).所有这些特点使得所提出的宽频地磁波监测仪能够满足子午工程二期的波探测需求.

CoFe/NiFe复合自由层对自旋阀磁电阻变化率的影响

研究CoFe/NiFe复合自由层对自旋阀磁电阻变化率的影响。在实验中通过固定溅射功率、时间和气流,调节靶基距(TSD)得到不同厚度及均匀性的复合自由层CoFe/NiFe薄膜,进而达到优化自旋阀结构提高其磁电阻率的目的。实验结果表明:在TSD分别为8.382 cm、8.890 cm时,制备的CoFe和NiFe单层膜性能最优,电阻标准偏差分别为1.33%、0.98%。通过磁性能综合测试平台对优化后的CoFe/NiFe复合自由层的自旋阀结构进行了测试,磁电阻变化率(MR)较优化前提高了约0.84%。该研究可为高性能自旋阀结构的制备提供参考。

基于TMR器件的弱磁传感系统设计

小型化高性能磁传感系统在磁异探测、航空航天、生物磁测量等领域具有重要的应用前景。传统磁传感系统因体积大、功耗高等原因难以搭载于无人机平台,而隧道磁电阻(TMR)器件是构建小型磁传感系统的理想选择。该文在分析TMR器件磁滞特性及其灵敏度与工作点关系的基础上,提出一种通过稳定TMR器件工作点来实现磁滞补偿的方法,通过建立磁场反馈补偿回路并采用自适应磁场补偿算法,大幅提升磁传感系统的性能。测试结果表明所设计的磁传感系统的测量范围为-10000~10000 nT,线性度为0.016%,噪声水平为0.39 nT/√Hz@1 Hz,带宽为60 Hz,可以满足水下磁异目标探测等应用需求。

磁阻式磁力齿轮多目标优化设计

结合磁阻式磁力齿轮工作原理及传动性能的分析,以提高电磁转矩和降低转矩脉动为目标进行优化设计。首先,通过田口实验设计方法筛选出对设计目标影响较大的因素,再采用响应面法得到反映优化参数与优化目标之间函数关系的数学模型。然后,进行基于多目标白鹭群优化算法的多目标优化设计,选出最优参数组合。最大输出转矩提高了7.76%,转矩脉动降低了28.76%。最后,通过有限元仿真验证了优化算法的有效性和可靠性,为磁阻式磁力齿轮的设计提供参考。

基于多TMR的涡流无损顶锤裂纹检测系统设计

针对碳化钨顶锤的表面及近表面裂纹的快速精准无损检测需求,开发了一套基于多个隧道磁阻的涡流裂纹探伤检测系统。系统设计了电源供电电路、频率可调节的信号发生电路、功率放大电路、检测探头,能检测出微缺陷引起的叠加磁场的变化。有限元仿真与顶锤检测实验的对比分析表明该检测系统可以准确识别顶锤的细微裂纹损伤,实现了基于涡流原理的顶锤钨合金试块近表面微小裂纹的检测。