Magnetoresistive Research Articles

Combined Technology Fabrication of Spin-Valve Magnetoresistive Elements and Micromagnets

We present the research results of the fabrication technology of magnetoresistive (MR) elements based on the multilayer spin-valve magnetoresistive (SVMR) Ta–FeNiCo–CoFe–Cu–CoFe–FeNiCo–FeMn–Та nanostructures and CoNi micromagnets for the construction of digital galvanic interchanges and the magnetic field sensors. The results of experimental studies of test elements based on multilayer SVMR nanostructures with an MR effect from 7 to 8% and films of magnetically hard materials with a coercive force of up to 95 Oe formed on a single silicon die are presented.

Hysteresis Suppressing of Modulated Magnetoresistive Sensors Using Bidirection Pulse Magnetization

1/f noise as well as nonlinear and hysteresis are the dominant restrictions of magnetoresistive (MR) sensors in detection ability. Modulation of the stimulating magnetic field of the MR sensors with microelectromechanical systems (MEMS) can reduce the 1/f noise by hundreds of times at low frequency, which gives a highlight for high-sensitive magnetic sensors. However, nonlinear response primarily caused by magnetic hysteresis is still a practical problem in modulated MR sensors, as well as unipolar response. In this paper, we propose a bidirection pulse magnetization method to reduce magnetic hysteresis, and in order to separate MR sensors from temperature influence, an integrated MEMS structure with low dissipation is developed to achieve pulse magnetization. Furthermore, this method is also used to achieve the bipolar magnetic field detection by distinguishing the response disparity under bidirection magnetization. The experimental results show that the modulated MR sensors can realize 90% reduction of hysteresis and 12.9% improvement of sensitivity with this method.

Measurement and Location of Multiple Corona Discharges Based on Tunneling Magnetoresistive Sensors

Measurement and Location of Multiple Corona Discharges Based on Tunneling Magnetoresistive Sensors

Magnetic field intensity effect on electrical conductivity of magnetorheological biosuspensions based on honey, turmeric and carbonyl iron

Magnetorheological biosuspensions (MRSs) are prepared using honey (HB), turmeric powder (nT) and carbonyl iron (CI) microparticles at various concentrations. By impregnating a cotton fabric with MRSs and compressing the whole system between two copper plates, a magnetoresistor (MRs) is obtained. The resistance R and electrical conductivity σ of MRs are measured as a function of time t for various values of magnetic field intensity H. We show that σ increases with H and is sensibly influenced by the volume fraction ΦCI of carbonyl iron. For fixed ΦCI and H, we show that σ increases with concentration ΦnT of turmeric powder.

Magnetoresistor with Planar Magnetic Concentrator as Wideband Contactless Current Sensor for Power Electronics Applications

High-frequency power electronic converters require lossless, accurate, and isolated current measurement. High-frequency currents through a printed circuit board (PCB) trace generate nonuniform magnetic field around the trace. The nonuniform magnetic fields can be normalized by means of magnetic field concentrators (MCONs) using conductive materials. In this study, a novel technique for high-frequency contactless current sensing using magnetoresistor (MR) sensors with planar magnetic concentrators (MCON) utilizing conductive materials has been proposed. The effect of different MCONs on the performance of anisotropic MR (AMR) sensors for high-frequency contactless current detection has been investigated. The performance of the AMR sensor equipped with different MCONs is demonstrated experimentally with respect to a fast rise step current. A detailed frequency analysis is performed on the sensor response with different MCONs to determine the effect on the detection bandwidth of the current sensors.

Read sensor technology for ultrahigh density magnetic recording

Abstract

Three-Dimensional CMOS Differential Folded Hall Sensor With Bandgap Reference and Readout Circuit

This paper presents a 3-D differential folded Hall sensor (HS) fabricated using standard 0.18- $\mu \text{m}$ CMOS technology; this HS includes 1-D folded lateral Hall sensor (FLHS) and 2-D folded vertical Hall sensor (FVHS). The proposed 3-D HS is laterally folded to reduce the effective conduction length and to decrease the offset voltage; a p+ guard ring is used to narrow the conducting channel and to improve magnetosensitivity. The magnetosensitivity is improved two-fold and the offset is eliminated using the differential topology. The proposed 1-D FLHS is sensitive to magnetic induction perpendicular to the chip plane BZ through the fast accumulation–slow release mechanism; the proposed 2-D FVHS is responsive to magnetic induction parallel to the chip plane, BX and BY, based on the interaction between the magnetoresistor (MR) and magnetotransistor, where MR is more dominant. Notably, the proposed 3-D HS operates with a small offset voltage of 0.26 mV and without magnetic hysteresis. For 2-D FVHS, at a voltage gain of 89.6 dB, the maximum sensor output $\Delta \text{V}_{\mathrm {{H}}}$ is approximately 196.4 mV at the applied magnetic induction of 5 mT and the maximum supply–current–related sensitivity SRI is approximately 5 943 V/ $\text{A}\cdot \text{T}$ at a current consumption of 6.25 mA for $x$ - or $y$ -channel. For 1-D FLHS, the maximum $\Delta \text{V}_{\mathrm {{H}}}$ is approximately 470.8 mV at 5 mT and the maximum SRI is approximately 14 790 V/ $\text{A}\cdot \text{T}$ at a bias current of 6.25 mA for $z$ -channel. The magntosensitivity SRI of 1-D FLHS is approximately 2.35 times that of 2-D FVHS. The designed 1-D FLHS is a comparable to the performance of other publications. However, it experiences a high nonlinearity error in output Hall voltage at a low bias current. By contrast, the proposed 1-D FLHS has a linear performance in output Hall voltage at a high bias current.

Analysis and Modeling of One-Dimensional Folded Vertical Hall Sensor With Readout Circuit

A Simulation Program with Integrated Circuit Emphasis macro model is proposed to simulate and understand the interaction between magnetoresistor (MR) and vertical magnetotransistor (VMT) in the proposed 1-D folded vertical Hall sensor (VHS), which was fabricated with 0.18- $\mu \text{m}$ 1P6M CMOS technology. In the proposed net-list file, the resistor MR enhances the linearity and the transistor VMT improves the magnetosensitivity between the induced Hall voltage and the applied magnetic induction. The folded design effectively eliminated the coupling Hall voltage that was generated by the Lorentz force. A readout circuit composed of a noninverting amplifier, low-pass filter, and instrumentation amplifier was also designed to enhance the magnetosensitivity, with a gain of 43 dB. Simulated and measured results verify the accuracy and flexibility of the proposed folded VHS. Measurements revealed that the maximum output Hall voltage $\text{V}_{\mathrm {{H}}}$ , optimum supply current-related magnetosensitivity, mean nonlinearity error, smallest offset, and relative bias current were 6.911 mV, 92.15 V/( $\text{A}\cdot \text{T}$ ), 10.26%, 42.61 mV, and 5 mA, respectively, for the proposed folded VHS with readout circuit at a load capacitor of 10 pF and a supplied voltage of 1.8 V. The VHS had good supply current-related magnetosensitivity because of the gain of the readout circuit.

Resolution improvement of low frequency AC magnetic field detection for modulated MR sensors.

Magnetic modulation methods especially Micro-Electro-Mechanical System (MEMS) modulation can improve the sensitivity of magnetoresistive (MR) sensors dramatically, and pT level detection of Direct Current (DC) magnetic field can be realized. While in a Low Frequency Alternate Current (LFAC) magnetic field measurement situation, frequency measurement is limited by a serious spectrum aliasing problem caused by the remanence in sensors and geomagnetic field, leading to target information loss because frequency indicates the magnetic target characteristics. In this paper, a compensation field produced with integrated coils is applied to the MR sensor to remove DC magnetic field distortion, and a LFAC magnetic field frequency estimation algorithm is proposed based on a search of the database, which is derived from the numerical model revealing the relationship of the LFAC frequency and determination factor [defined by the ratio of Discrete Fourier Transform (DFT) coefficients]. In this algorithm, an inverse modulation of sensor signals is performed to detect jumping-off point of LFAC in the time domain; this step is exploited to determine sampling points to be processed. A determination factor is calculated and taken into database to figure out frequency with a binary search algorithm. Experimental results demonstrate that the frequency measurement resolution of the LFAC magnetic field is improved from 12.2 Hz to 0.8 Hz by the presented method, which, within the signal band of a magnetic anomaly (0.04-2 Hz), indicates that the proposed method may expand the applications of magnetoresistive (MR) sensors to human healthcare and magnetic anomaly detection (MAD).

Magnetoresistive Effect of Amorphous In-Ga-Zn-O Magnetic Field Sensors

Magnetoresistive (MR) sensors made with amorphous In-Ga-Zn-O (a-IGZO) that have significant conventional or inverse MR effects at room temperature were fabricated. A high-temperature a-IGZO MR thin-film transistor exhibited a giant inverse MR effect of up to −69% at 25 mT. The detailed measurement results are reported and the mechanism for generation of the MR effect is discussed.

Self-assembled thin films of Fe3O4-Ag composite nanoparticles for spintronic applications

Controlled self-assembly of multi-component magnetic nanoparticles could lead to nanomaterial-based magnetic devices with novel structures and intriguing properties. Herein, self-assembled thin films of Fe3O4-Ag composite nanoparticles (CNPs) with hetero-dimeric shapes were fabricated using interfacial assembly method. The CNP-assembled thin films were further transferred to patterned silicon substrates followed by vacuum annealing, producing CNP-based magnetoresistive (MR) devices. Due to the presence of intra-particle interfaces and inter-particle barriers, an enhanced MR ratio and a non-linear current-voltage relation were observed in the device. The results of this work can potentially pave the way to the future exploration and development of spintronic devices built from composite nanomaterials.

Toward pTesla Detectivities Maintaining Minimum Sensor Footprint With Vertical Packaging of Spin Valves

The reduction of the noise level of magnetoresistive (MR) micrometric sensors is often achieved by increasing the sensor area and/or connecting MR elements in large arrays. This paper introduces an innovative strategy to increase the sensing area without increasing the area occupied by the MR sensors on a wafer, therefore minimizing the sensor footprint. Here, the idea is to deposit vertically spin-valve (SV) films, separated by an insulator. This packed structure is then incorporated into arrays, connected in parallel and series, as a general noise reduction strategy. Using calculations, the number of SVs vertically packed ( $Z$ ), combined in series ( $X$ elements) and parallel ( $Y$ elements) was investigated, so that the optimum geometry, which minimizes the field detectivity, can be obtained. The magnetic field detection of SV sensors in the thermal noise limit can be improved from 39 pT/Hz $^{1/2}$ for $Z = 1$ with a total number of 500 SVs (distributed in plane) to 12 pT/Hz $^{1/2}$ for $Z =10$ with a total number of 5000 SVs. Besides, the device footprint is also demonstrated to decrease from 0.7 mm2 ( $Z = 1$ ) to 0.07 mm2 ( $Z = 10$ ). These limits of detection are competitive with single SV sensors using magnetic flux concentrators, with the advantage of a high spatial resolution with fewer fabrication steps (at least three).

Advanced NDT Inspection Tools for Titanium Surfaces Based on High-Performance Magnetoresistive Sensors

Eddy current testing (ECT) is a high impact technology to detect surface flaws. However, its reliability is reduced for low conductive titanium alloys, which are broadly integrated into the industry. ECT tools based on magnetoresistive (MR) sensors offer advantages over inductive sensors due to an enhanced spatial resolution, high sensitivity, and bandwidth. In this paper, we demonstrate successful non-destructive testing inspection of titanium surfaces, not achieved by other ECT tools. Here, single surface defect (length = 0.6 mm; width $=100~\mu \text{m}$ ; depth $=50~\mu \text{m}$ ) in a non-polished TA6V $\alpha $ titanium mock-up was measured using an MR-ECT probe. The detection was made by an array of magnetic tunnel junctions with $50 \times 50~\mu \text{m}^{\mathrm { {2}}}$ with optimized field detectivity. A differential measurement employing a heterodyne technique isolated the magnetic field component ( $f_{H}- f_{\mathrm { {bias}}} = 1$ kHz) from the electric biasing component ( $f_{\mathrm { {bias}}} = 4999$ kHz) and electromagnetic coupling ( $f_{H} = 5$ MHz), revealing a bipolar defect signature of $6.01~\mu \text{V}_{\text {0-p}}$ amplitude.

Numerical Evaluation of Bacterial Cell Concentration by Magnetoresistive Cytometry

The bacterial infection degree of a real biological sample can be determined by using magnetoresistive (MR) cytometry. In this case, it is required to count detection events and to precisely determine the bacterial cells concentration detected by the sensor in each detection event. Here, we are proposing a method to evaluate the bacterial concentration from experimental obtained data. By simulating and analyzing the signals created by clusters with a different number of cells, shapes, and orientations relative to the sensor sensitive direction, clusters that can fit the experimental signals are found. The simulation results are compared with the experimental obtained signals in order to quantify the number of cells that are detected by the MR sensor in different detection events.

On-Site Non-Invasive Current Monitoring of Multi-Core Underground Power Cables With a Magnetic-Field Sensing Platform at a Substation

Current monitoring can facilitate preemptive action in electrical distribution network, so as to relieve power congestion, improve transmission efficiency, and ensure network reliability. The non-invasive current sensing devices are promising since they do not require contacting hazardous high voltage and their installation is much easier compared with invasive current sensing devices. However, the existing non-invasive current sensing devices, such as current clamps and Rogowski coils are only applicable for measuring single-core underground power cables. In this paper, we established a non-invasive technique, that can monitor the currents of a multi-core underground power cable by measuring the emitted magnetic field around the cable surface. The additional magnetic fields generated by induced and leakage currents on the cables were firstly evaluated. Magnetoresistive (MR) sensors in a circular array were adopted to measure magnetic field around the cable surface, and a triple-layer shielding was designed to reduce the effects of external interference. Regarding intrinsic noise in MR sensors (e.g., 1/f noise and thermal noise), magnetic flux concentrators were supplemented to improve the signal-to-noise ratio. The developed platform was tested in a substation, and the reconstructed results closely matched the real geometrical configuration and current records of the tested cable. Apart from the non-invasive feature, the platform also shows great potential to improve the sensing capability of current amplitude and frequency compared with CTs by adopting MR sensors.

First-principles study on magnetic tunneling junctions with semiconducting CuInSe2 and CuGaSe2 barriers

We theoretically investigate two magnetic tunneling junctions (MTJs) with different semiconductor barriers, CuInSe2 (CIS) and CuGaSe2 (CGS), sandwiched between Fe electrodes. We find that Δ1 wave functions provide dominant contributions to spin-dependent tunneling transport in both CIS- and CGS-based MTJs. We also find that the CGS-based MTJ has a much higher magnetoresistive (MR) ratio than the CIS-based MTJ, which indicates that a higher MR ratio is expected for a higher Ga concentration x in the recently reported CuIn1−xGaxSe2-based MTJs. Furthermore, we show that the CIS- and CGS-based MTJs have much smaller resistance–area products (RA) than the conventional MgO-based MTJs.

Hysteresis Compensation Method for Magnetoresistive Sensors Based on Single Polar Controlled Magnetic Field Pulses

This paper presents an improved hysteresis compensation method based on magnetic field pulses. The magnetic field pulses are generated by current pulses applied to a one-winding coil structure on the top of the sensor element. This configuration allows the sensor electronic to drive a magnetoresistive (MR) sensor in its magnetic saturation. Anisotropic magnetoresistance, giant magnetoresistance, and tunnel magnetoresistance current sensors are chosen for conducting experiments. The magnetic field generated by current pulses and the magnetic field generated by the current to be measured always have to be in the same direction. As a result, the output characteristic of an MR current sensor can always be kept on the negative rising and the positive falling branch of the magnetic major loop during the measurement. Thus, a defined output of the MR current sensor independent from the magnetic history for all current values can be achieved. An electronic mixed signal circuit consisting of a field-programmable gate array, an optoisolator, analog switches, and attention display converters is used to generate the current pulses and to measure the output of the current sensor. Current measurements with and without controlled magnetic field (current) pulses are compared. A hysteresis reduction to nearly 20% of the original value, by using this hysteresis compensation method, was reached.

Magnetoresistance and transport properties of (LSMO)(1−x) –(SBT)(x) (x = 0.0, 0.13, 0.23) composite thin films on silicon substrate

0–3 manganite-rich composite thin film composed of (1 − x) La0.67Sr0.33MnO3 + (x) SrBi2Ta2O9 with x = 0.0, 0.13, 0.23 (abbreviated as LSMO-SBTx) was fabricated by pulsed laser deposition on silicon substrate. The microstructure, electrical, magnetoresistive (MR) and transport properties of the composites were investigated systematically. X-ray diffraction and cross-sectional microstructural studies of LSMO-SBTx samples prove the presence of both LSMO and SBT phases with SBT grains embedded in the LSMO matrix. SBT grains are seen surrounded and covered by LSMO grains making it a 0–3 composite. The incorporation of the insulating ferroelectric SBT phase leads to a substantial increase in resistivity of the composites. Temperature-dependent resistivity measurement showed a shift of the peak Tp (or TM-I) from 200 to 114 K with the increase in the ferroelectric phase. Three conduction models were explored to describe the transport behaviors in different temperature regions. The dominant electron transport mechanism above TM-I has been found to be variable range hopping for Tp < T < θD/2, where θD is the Debye temperature, and the adiabatic small polaronic model for T > θD/2. Since the films were of high disorder, the electron–electron and electron–phonon scatterings have been found to play the dominant role in deciding the resistivity at low temperatures. A comparison between the MR plot for the three samples at 100 K found the LFMR peak to be present in both the LSMO-SBT0.13 and LSMO-SBT0.23 samples, but absent for the LSMO-SBT0 sample. At a temperature of 10 K and at a field of 6 kOe, the MR value was 6%, 12%, and 16% for LSMO-SBT0, LSMO-SBT0.13, and LSMO-SBT0.23, respectively.

Rapid and specific detection of cell-derived microvesicles using a magnetoresistive biochip.

Microvesicles (MVs) are a promising source of diagnostic biomarkers which have gained a wide interest in the biomedical and biosensing field. They can be interpreted as a "fingerprint" of various diseases. Nonetheless, MVs implementation into clinical settings has been hampered by the lack of technologies to accurately characterize, detect and quantify them. Here, we report the specific sensing and quantification of MVs from endothelial cells using a portable magnetoresistive (MR) biochip platform, in less than one hour and within physiologically relevant concentrations (1 × 108 MVs per ml). MVs were isolated from both endothelial and epithelial cells undergoing apoptosis, and characterized by atomic force microscopy (AFM) and nanoparticle tracking analysis (NTA), which revealed similar MV sizes. Importantly, our results showed that the two distinct MV populations could be discriminated with the MR biochip platform, with over a 5-fold capture efficiency of endothelial MVs in comparison to the control (epithelial MVs). Also, unspecific binding of MVs to BSA was less than 1% of the specific signal. The detection strategy was based on a sandwich immunoassay, where MVs were labelled with magnetic nanoparticles (MNPs) functionalized with Annexin V and then captured by anti-CD31 antibodies previously immobilized on the surface of the sensor. Results suggest that this approach allows the detection of specific MVs from complex samples such as serum, and highlight the potential of this technology to become a suitable tool for MVs detection as a complementary method of diagnosis.

Silicon Carbide and Magnetorresistive Technologies for Solid State Power Controllers

The aim of this paper is to make an introduction, review and preliminary investigation tasks of the application of Silicon Carbide (SiC) power semiconductors and magnetoresistive (MR) current sensors for Solid State Power Controllers (SSPCs) and controlled switches, especially for high temperature environment and/or high voltage applications.