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.

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.

Effects of substrate temperature and annealing on the anisotropic magnetoresistive property of NiFe films

Ni_(83)Fe_(17) films with a thickness of about 100 nm were deposited onthermal oxidized silicon substrates at ambient temperature, 240, 350, and 410℃ by DC magnetronsputtering. The deposition rate was about 0.11 nm/s. The as-deposited films were annealed at 450,550, and 650℃, respectively, in a vacuum lower than 3 x 10~3 Pa for 1 h. The Ni_(83)Fe_(17) filmsmainly grow with a crystalline orientation of [111] in the direction of the film growth. With theannealing temperature increasing, the [111] orientation enhances. For films deposited at all fourdifferent temperatures, the significant improvement on anisotropic magnetoresistance occurs at theannealing temperature higher than 550℃. But for films deposited at ambient temperatures and 240 ℃,the anisotropic magnetoresistance can only rise to about 1% after 650 ℃ annealing. For filmsdeposited at 350℃ and 410℃, the anisotropic magnetoresistance rises to about 3.8% after 650℃annealing. The atomic force microscopy (AFM) observation shows a significant increase in grain sizeof the film deposited at 350℃ after 650℃ annealing. The decrease in resistivity and the increasein anisotropic magnetoresistance are caused by the decrease in point defects, the increase in grainsize, and the improvement in lattice structure integrity of the films.

Research progress in anisotropic magnetoresistance

Anisotropic magnetoresistance （AMR） is an important physical phenomenon that has broad application potential in many relevant fields. Thus, AMR is one of the most attractive research directions in material science to date. In this article, we summarize the recent advances in AMR, including traditional permalloy AMR, tunnel AMR, ballistic AMR, Coulomb blockade AMR, anomalous AMR, and antiferromagnetic AMR. The existing problems and possible challenges in developing more advanced AMR were briefly discussed, and future development trends and prospects were also speculated.

Anisotropic Magnetoresistance Effect in Amorphous and Nanocrystalline Fe(Cu,Nb)-Si-B Alloys

The magnetoresistance effect and magnetic properties in amorphous and nanocrystalline Fe(Cu, Nb)-Si-B ribbons have been investigated, it was observed that the anisotropic magnetoresistance (AMR) of nanocrystalline alloy is much smaller than that of amorphous alloy, Indicating that the anisotropy of nanocrystalline alloy becomes smaller after crystallizing, and the smallest AMR is coincident with the excellent soft magnetic characteristics. It is believed that the smaller magnetic crystalline anisotropy is the origin of the excellent soft magnetic characteristics of nanocrystalline alloy.

Anisotropic Magnetoresistivity in Semimetal TaSb_2

We investigate the anisotropic magnetic transports in topological semimetal TaSb2. The compound shows the large magnetoresistance（MR） without saturation and the metal-insulator-like transition no matter whether the magnetic field is parallel to c-axis or a-axis, except that the MR for B‖c is almost twice as large as that of B‖a at low temperatures. The adopted Kohler＇s rule can be obeyed by the MR at distinct temperatures for B‖c,but it is slightly violated as B‖a. The angle-dependent MR measurements exhibit the two-fold rotational symmetry below70 K,consistent with the monoclinic crystal structure of TaSb2. The dumbbell-like picture of angle-dependent MR in TaSb2 suggests a strongly anisotropic Fermi surface at low temperatures. However, it finally loses the two-fold symmetry over 70 K, implying a possible topological phase transition at around the temperature where Tm is related to a metal-insulator-like transition under magnetic fields.

Temperature Dependent In-Plane Anisotropic Magnetoresistance in HfTe_(5) Thin Layers

We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe_(5) thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T_(p).Below T_(p),the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe_(5) thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.

Anomalous anisotropic magnetoresistance in single-crystalline Co/SrTiO_(3)(001)heterostructures

The anisotropic magnetoresistances(AMRs)in single crystalline Co(6 nm)/SrTiO_(3)(001)heterostructures from 5 K to 300 K with the current direction setting along either Co[100]or Co[110]are investigated in this work.The anomalous(normal)AMR is observed below(above)100 K.With the current along Co[100]direction,the AMR shows negative longitudinal and positive transverse magnetoresistances at T<100 K,while the AMR is inverse with the current along Co[110].Meanwhile,the amplitude ratio between Co[110]and Co[100]is observed to be as large as 29 at 100 K.A crystal symmetry-adapted model of AMR demonstrates that interplay between the non-crystalline component and crossed AMR component results in the anomalous AMR.Our results may reveal more intriguing magneto-transport behaviors of film on SrTiO_(3)or other perovskite oxides.

Gate-Voltage-Induced Magnetization Reversal and Tunneling Anisotropic Magnetoresistance in a Single Molecular Magnet with Temperature Gradient

We study the coutrol of gate voltage over the magnetization of a single-molecule magnet （SMM） weakly coupled to a ferromagnetic and a normal metal electrode in the presence of the temperature gradient between two electrodes. It is demonstrated that the SMM＇s magnetization can change periodically with periodic gate voltage due to the driving oI the temperature gradient. Under an appropriate matching of the electrode polarization, the temperature difference and the pulse width of gate voltage, the SMM＇s magnetization can be completely reversed in a period of gate voltage. The corresponding flipping time can be controlled by the system parameters. In addition, we also investigate the tunneling anisotropic magnetoresistance （TAMFt） of the device in the steady state when the ferromagnetic electrode is noncollinear with the easy axis of the SMM, and show the jump characteristic of the TAMR.

Sign reversal of anisotropic magnetoresistance and anomalous thickness-dependent resistivity in Sr_(2)CrWO_(6)/SrTiO_(3) films

High-quality Sr_(2)CrWO_(6)(SCWO) films have been grown on SrTiO_(3)(STO) substrate by pulsed laser deposition under low oxygen pressure. With decrease of the film thickness, a drastic conductivity increase is observed. The Hall measurements show that the thicker the film, the lower the carrier density. An extrinsic mechanism of charge doping due to the dominance of oxygen vacancies at SCWO/STO interfaces is proposed. The distribution and gradient of carrier concentration in SCWO films are considered to be related to this phenomenon. Resistivity behavior observed in these films is found to follow the variable range hopping model. It is revealed that with increase of the film thickness, the extent of disorder in the lattice increases, which gives a clear evidence of disorder-induced localization charge carriers in these films.Magnetoresistance measurements show that there is a negative magnetoresistance in SCWO films, which is considered to be caused by the magnetic scattering of magnetic elements Cr^(3+) and W^(5+). In addition, a sign reversal of anisotropic magnetoresistance(AMR) in SCWO film is observed for the first time, when the temperature varies across a characteristic value, T_(M). Magnetization-temperature measurements demonstrate that this AMR sign reversal is caused by the direction transition of easy axis of magnetization from the in-plane ferromagnetic order at T > T_(M) to the out-of-plane at T < T_(M).

Modelling Magnetoresistance Effect in Limited Anisotropic Semiconductors

A macroscopic model of the magnetoresistance effect in fimited anisotropic semiconductors is built. This model allows us to solve the problem of measurement of physical magnetoresistance components of crystals and films. Based on a unified mathematical model the method is worked out enabling us to measure tensor components of the specific electrical resistance and the relative magnetoresistance of anisotropic semiconductors simultaneously.

Mn_(3)Sn薄膜磁相变的输运表征

六角笼目(Kagome)相拓扑反铁磁材料近年来引起了人们极大的研究兴趣,这主要是因为它们拥有众多独特的性能,例如虽然净磁矩跟反铁磁材料一样接近零,但确有与铁磁性材料强度相当的磁电、磁光和磁热效应,极具应用价值.以上的这些特性绝大多数都与其磁结构紧密相关,然而人们却发现其磁结构对于生长条件和材料成分非常敏感.因此,开发一种简单、普适的Kagome相拓扑反铁磁材料磁结构相变测量方法,对于大多数难以获得高能中子衍射等先进实验手段的实验室来说,无论是材料的生长优化还是物理现象机理的理解都具有重要的意义.本文采用脉冲激光沉积方法在(1102)取向的Al_(2)O_(3)单晶衬底上成功外延制备了高质量(1120)取向的六角Kagome相Mn_(3)Sn薄膜,并系统地测量了不同温度下该Mn_(3)Sn薄膜的磁性和磁输运特性.结果发现,该Mn_(3)Sn薄膜的磁化曲线、霍尔电阻率曲线和磁电阻曲线在其三类磁相变温度中的某些或全部均表现出一定的异常特征.这些特征可以作为该六角Kagome相Mn_(3)Sn薄膜中磁相变的证据,甚至用于测量这些磁相变的温度.本工作有助于进一步推动六角Kagome相拓扑反铁磁材料在自旋电子器件中的应用.

AMR磁栅尺磁头输出波形的半次谐波现象与分析

对采集到的AMR磁栅尺磁头输出波形进行了付里叶谐波分析,发现了波形中的半次谐波现象.对该现象产生的原因以及半次谐波幅度与磁头水平偏角的关系进行了定性分析.磁头水平偏角为零时输出波形不含半次谐波,磁头水平偏角越大,半次谐波幅度就越高;在偏角小于3°的小角度范围内,两者之间基本上是一个线性关系;磁头水平偏角的正负变化会引起半次谐波项正负的变化.结果对正确使用AMR薄膜磁电阻磁头,提高磁栅尺测量系统的精度有指导意义.

NiFe薄膜AMR元件中非均匀退磁场和宽度的相关性

采用磁控溅射方法制备了NiFe各向异性磁电阻(AMR)薄膜,经过光学曝光及离子刻蚀将NiFe薄膜制成了厚度t=20 nm、长度l=2．5 mm、宽度w分别为50,20,10,5和μm的AMR元件．测量了AMR元件的磁电阻效应．考虑沿宽度方向退磁场的非均匀性,计算了磁电阻比率．结果表明,宽度决定了AMR元件中的退磁场分布和边缘退磁场的大小,直接影响着AMR元件的磁化反转过程．宽度越小,元件中的边缘退磁场越大,在外磁场下的磁化反转也越困难．在磁化反转过程中,磁化反转先从中心开始,逐渐扩展到边缘．

一种具有消谐波正弦输出的AMR薄膜磁头设计

设计了一种消谐波正弦输出的AMR磁头,这种磁头是由AMR金属薄膜材料经过微加工工艺制成。通过对磁头输出波形的谐波分析和测试,表明该磁头具有优良的正弦输出特性、磁场灵敏度和信噪比,可以广泛应用于高精度磁栅位移检测和磁旋转编码器角度测量系统中。

基于PI闭环控制的AMR磁阻传感器信号调理电路

为了提高磁场测量精度,提出一种基于PI闭环控制的AMR磁阻传感器信号调理电路。该电路由前置放大器、开关同步检波、积分电路和闭环反馈电路组成。首先通过选取较小的前置放大器增益,以降低对传感器输出噪声的放大;然后利用积分器对放大后信号进行积分,得到积分电压;最后,将积分电压进行V/I转换,并将电流接入HMC1001偏置电流带,实现闭环反馈,以抵消外部待测磁场,当电路平衡时,传感器工作于零场,积分输出电压正比于待测磁场。与开环结构对比实验结果表明:在相同的灵敏度条件下,闭环式信号调理电路噪声功率谱密度为40 pT/√ Hz @1 Hz,并且与开环式的信号调理电路相比,它的输出信号信噪比提高了15.55 dB。

薄膜宽度对于NiFe/Ta逆自旋霍尔效应影响的自动表征

通过分立模板镀膜法在同一块光刻版上设计了不同宽度的NiFe/Ta双层膜线条,采用磁控溅射镀膜制备样品。构建了自动化电测试系统实现批量测试样品的逆自旋霍尔电压信号。实验结果表明,样品宽度会影响测试电压信号的对称性和幅值,通过拟合得到信号的对称分量和反对称分量及其比值随着样品宽度的变化,并分析逆自旋霍尔电压和自旋整流电压的影响因素,发现随着样品宽度的减小,自旋整流效应带来的影响逐渐减小,且施加的微波磁场越大,这种变化越明显,其原因在于各向异性磁电阻对薄膜宽度的依赖性。研究结果对自旋电子器件的实用提供重要的设计依据和指导。

三种AMR磁头性能比较

各向异性磁电阻磁头(AMR)用于服务器磁带机上的数据储存,并不断推出更高性能的产品。本文分析与比较了Tandberg公司的三种各向异性磁电阻磁头(SLR7、SLR100、LTO2)的设计参数,详细地研究了磁头的关键功能测试参数,如读错误率(Read Error Rate)和Viterbi Distance(VD),从而对影响磁头性能的设计参数有了详细的了解。磁电阻材料NiFe和偏转磁场材料CoZrMo的厚度,对各向异性磁电阻磁头性能起着关键作用,直接影响磁头储存数据的能力。

改善AMR薄膜磁电阻传感器线性度的几种方法

在分析金属薄膜磁电阻传感器非线性产生原因的基础上,提出了几种设计AMR(各向异性磁电阻)薄膜磁电阻传感器时改善其线性度的方法.用直流磁控溅射方法制备了Ni80Fe20和Ni65Co35AMR薄膜材料;用微加工工艺制做出了几种AMR传感器元件,并给出了测试结果.

各向异性磁电阻AMR在永磁同步电机控制中的应用

新能源汽车的永磁同步电机,基于定向矢量控制技术,电机转子位置传感器普遍采用磁阻式旋转变压器,相比传统技术,磁阻(MR)位置测量具有多种优势。可靠性、精度和整体鲁棒性是推动磁阻检测技术快速发展的主要因素。本文基于各向异性磁电阻AMR传感器低成本、相对较小的尺寸、非接触式操作、宽温度范围、对灰尘和光的不敏感性、宽磁场范围,这些特性在永磁同步电机控制中的应用前景广泛。相比与旋变传感器,体积更小,便于安装且成本更低。