Planar Hall Sensors Research Articles

Planar Hall effect in the quasi-two-dimensional topological semimetal candidate In0.93TaSe2

Here, we report the systematic study on the planar transport properties of the quasi-two-dimensional (quasi-2D) topological nodal-line semimetal candidate In0.93TaSe2. When rotating magnetic field in the plane, the anisotropic longitudinal resistance and planar Hall resistance are clearly observed and can be well described by the theoretical formulation of the planar Hall effect (PHE). Further analysis demonstrates that the anisotropic orbital resistance rather than the topological-nontrivial chiral anomaly plays a dominant role on the PHE in In0.93TaSe2. Our study provides another platform for understanding the mechanism of PHE, which may also be valuable for future planar Hall sensors based on quasi-2D materials.

Research on the manufacture of equipment for detecting defects of disjointed, small diameter steel pipes by magnetic flux leakage method

This paper presents a design and pilot fabrication of the EMI (electromagnetic inspection) device to meet the requirements of non-destructive inspection of defects on straight, small diameter, variable drill pipes. The improved feature of this device is to replace the normal Hall sensor with the planar Hall sensor with high sensitivity, temperature and time stability to investigate the magnetic field variation caused by the variation of tube thickness. The test unit for detecting longitudinal defects has a new structure with a magnetic field that is magnetised along the circumference of the tube by an electromagnet. The magnetisation system and the test tube do not need to rotate during the measurement. The EMI equipment is expected to be tested at the Electromechanical Enterprise of Vietsovpetro.

Design and Optimisation of Elliptical-Shaped Planar Hall Sensor for Biomedical Applications.

The magnetic beads detection-based immunoassay, also called magneto-immunoassay, has potential applications in point-of-care testing (POCT) due to its unique advantage of minimal background interference from the biological sample and associated reagents. While magnetic field detection technologies are well established for numerous applications in the military, as well as in geology, archaeology, mining, spacecraft, and mobile phones, adaptation into magneto-immunoassay is yet to be explored. The magnetic field biosensors under development tend to be multilayered and require an expensive fabrication process. A low-cost and affordable biosensing platform is required for an effective point-of-care diagnosis in a resource-limited environment. Therefore, we evaluated a single-layered magnetic biosensor in this study to overcome this limitation. The shape-induced magnetic anisotropy-based planar hall effect sensor was recently developed to detect a low-level magnetic field, but was not explored for medical application. In this study, the elliptical-shaped planar hall effect (EPHE) sensor was designed, fabricated, characterized, and optimized for the magneto-immunoassay, specifically. Nine sensor variants were designed and fabricated. A customized measurement setup incorporating a lock-in amplifier was used to quantify 4.5 µm magnetic beads in a droplet. The result indicated that the single-domain behaviour of the magnetic film and larger sensing area with a thinner magnetic film had the highest sensitivity. The developed sensor was tested with a range of magnetic bead concentrations, demonstrating a limit of detection of 200 beads/μL. The sensor performance encourages employing magneto-immunoassay towards developing a low-cost POCT device in the future.

Planar Hall sensor for quantitative measurement of pipe wall thickness reduction based on the magnetic flux density method

Quantitatively monitoring the thickness reduction of a pipe by using magnetic flux density method remains a major challenge due to the small and gradual change in magnetic flux density over a long distance along a pipe. This signal change is hindered in the background signal of a detector that has a high temperature dependence and unstable background signal. In this paper, we verify the effectiveness of magnetic flux density method in quantitatively monitoring thickness reduction through simulation and experimental verification. Experimental results show that the proportion of magnetic signal change is 1.4 mT per 10% wall loss. To support this quantitative approach, we optimise an original ultra-high-sensitivity planar Hall sensor with high thermal stability and stable background signal versus time for measurement of the magnetic field over a wide range from 0 to 50 mT. The quantitative measurements were validated on test pipes with varying thickness steps of 0.5 mm.

Reduced thermal dependence of the sensitivity of a planar Hall sensor

The ability to stabilize the sensitivity of a magnetoresistance sensor in unstable thermal environments is a key parameter in many high precision measurements. Here, we propose a method to stabilize the sensitivity of a highly sensitive and low noise magnetic sensor based on a planar Hall Effect crossed junction. The stability is achieved by controlling the interplay between Zeeman energy, exchange bias energy, and anisotropy energy as a function of the temperature of the sensor stack comprising a trilayer structure NiFe/Cu/IrMn (10/0.12/10 nm). The high thermal stability of the sensor sensitivity of 4.5 ± 0.15 × 10−3 V/A/T/K is achieved when the external magnetic field is set around ±2 ± 0.04 mT and the applied current is fixed at 20 mA in the temperature range of 110 K–360 K. This method improves the magnetic sensor detection by about an order of magnitude, enabling its deployment in various research fields, particularly to study magnetic properties of small quantities of magnetic materials toward the detection of single magnetic objects, which was impossible before.

Interface-induced enhancement of sensitivity in NiFe/Pt/IrMn-based planar hall sensors with nanoTesla resolution

The planar Hall sensitivity of obliquely deposited NiFe(10)/Pt(tPt) /IrMn(8)/Pt(3) (nm) trilayer structures has been investigated by introducing interfacial modification and altering sensor geometry. The peak-to-peak PHE voltage and AMR ratio of the sensors exhibit an oscillatory increase as a function of Pt thickness up to 1 nm. This behaviour has been attributed to the strong electron spin-orbit scattering at the NiFe/Pt interface of the trilayers. The magnetic field resolution of 380 nT has been observed for the sensor with a spacer layer of 9 Å. The temperature-dependent PHE measurements indicate that the sensors continue to operate at 390 K with a sensitivity of 5.1 μV/(Oe·mA). In order to further increase the sensitivity, the PHE sensors have been fabricated for a fixed Pt thickness of 8 Å by using the sensor architectures of a cross, tilted-cross, 1-ring, and 5-ring junctions. A sensitivity of 3.8 μV/(Oe·mA) has been obtained for the cross junction, while it considerably increased to 299 μV/(Oe·mA) for 5-ring sensor geometry. The real-time voltage profile of the PHE sensors demonstrates that the sensor states are very stable under various magnetic fields and sensor output voltages turn back to their initial offset values. This provides a great potential for the NiFe/Pt/IrMn-based planar Hall sensors in many sensing applications.

Shapeable Planar Hall Sensor With a Stable Sensitivity Under Concave and Convex Bending

A shapeable planar Hall sensor has been fabricated by lift-off a bilayer structure of NiFe(10 nm)/IrMn (8 nm) grown on a Kapton/PDMS substrate without using a buffer layer. The sensor exhibits a magnetic field sensitivity of 0.74 $\mu$V/Oe.mA and provides a stable response under repetitive ON/OFF experiments. The concave and convex bending measurements indicate that the AMR voltage of the sensor is very sensitive to the stress and strain. However, the planar Hall sensitivity is independent from them with a stable linear region and unchanged peak positions in the magnetic field axis. This type of behaviour has been observed for the first time in the planar Hall sensors. Therefore, this novel device can fulfill simultaneous multifunctional sensing of small magnetic fields, stress and strain. This makes it promising for tactile sensing applications in humanoid robotics.

Localized detection of reversal nucleation generated by high moment magnetic nanoparticles using a large-area magnetic sensor

This report introduces a local-magnetic-reversal-nucleation based giant magnetoresistance (GMR) sensor with a large sensing area and further discusses its novel sensing scheme of high magnetic moment nanoparticles (MNPs). We demonstrated experimentally that this large-area GMR sensor could successfully detect high moment MNPs. The detection scheme of localized reversal nucleation of GMR sensor induced by MNPs was analyzed and further confirmed by the micromagnetic simulations. This work may provide one pathway in designing next generation GMR biosensors with large area and high sensitivity. This sensing scheme could be applicable to other magnetic biosensors such as magnetic tunnel junction sensors and planar Hall sensors.

High-sensitivity planar Hall sensor based on simple gaint magneto resistance NiFe/Cu/NiFe structure for biochip application

The planar Hall effect (PHE) sensor based on a simple giant magneto resistance (GMR) trilayer structure NiFe/Cu/NiFe has been designed and fabricated successfully using conventional clean room fabrication methods. The PHE sensor is integrated by 24 sensor patterns with dimensions of 50 × 50 μm. Influence of individual layer thickness to sensitivity of sensor has been investigated. Sensitivity and planar Hall voltage increases with the decrease of Cu-layer thickness. The results are discussed in terms of the reinforcement of the antiferromagnetic interaction between NiFe layers and shunting current through the layer Cu. The optimum configuration has been found in the structure with the Cu-layer of 1 nm. In this case a single planar Hall effect sensor exhibits a high sensitivity of about 8 μV Oe−1 and a maximal of the signal change as large as ▵V ∼ 55 μV. These values are comparable to those of the typical PHE sensor based on complex GMR spin-valve structure. With a high sensitivity and simple structure, this sensor is very promising for practical detection of magnetic beads and identifying multiple biological agents in the environment.

High field-sensitivity planar Hall sensor based on NiFe/Cu/IrMn trilayer structure

A trilayer structure, which has weak exchange coupling and high active current, has been optimized emphasizing for high field-sensitivity planar Hall effect (PHE) sensor. To illustrate the high field sensitivity of the PHE sensor, three different structures are fabricated: a bilayer thin film Ta(3)/NiFe(10)/IrMn(10)/Ta(3) (nm), a spin-valve thin film Ta(3)/NiFe(10)/Cu(1.2)/NiFe(2)/IrMn(10)/Ta(3) (nm), and a trilayer thin film Ta(3)/NiFe(10)/Cu(0.12)/IrMn(10)/Ta(3) (nm). The characterized results reveal that the field sensitivity of PHE sensor based on trilayer thin film is about one order larger than that of bilayer and is about twice larger than that of spin-valve thin film. Moreover, in trilayer structure, the thinner spacer layer gives the better performance. When the nominal thickness of spacer Cu layer is the smallest, the PHE sensor exhibits the best performance, i.e., in this experiment, it is about 0.12 nm.

Spin-valve planar Hall sensor for single bead detection

The planar Hall effect (PHE) sensor with a junction size of 3 μm × 3 μm for a single micro-bead detection has been fabricated successfully using a typical spin-valve thin film Ta(5)/NiFe(16)/Cu(1.2)/NiFe(2)/IrMn(15)/Ta(5) nm. The PHE sensor exhibits a sensitivity of about 7.2 μV Oe −1 in the magnetic field range of ±7 Oe approximately. We have performed an experiment to illustrated the possibility of single micro-bead detection by using a PHE sensor. A single micro-bead of 2.8 μm diameter size is secluded from 0.1% dilute solution of the Dynabeads ® M-280 dropped on the sensor surface and is located on the sensor junction by using a micro magnetic needle. The comparison of the PHE voltage profiles in the field range from 0 to 20 Oe in the absence and presence of a single micro-bead identifies a single Dynabeads ® M-280, the maximal signal change as large as Δ V ∼ 1.1 μV can be obtained at the field ∼6.6 Oe. The results are well described in terms of the reversal of a basic single domain structure.

Temperature effects in exchange-biased planar hall sensors for bioapplications

The temperature dependence of exchange biased planar Hall effect sensors is investigated between T = −10 and 70 °C. It is shown that a single domain model describes the system well and that the temperature coefficient of the low-field sensitivity at T = 25 °C is 0.32%/°C. A procedure for temperature correction by use of a reference sensor is demonstrated. Consequences for magnetic biosensing are exemplified with calculations on M-280 Dynabeads ®.

The contribution of the exchange biased field direction in multilayer thin films to planar Hall resistance

AbstractRecently, planar Hall effect (PHE) has been widely pursued due to its application potential for biosensors. Planar Hall sensor is based on the anisotropy magnetoresistance and exhibits many advantages, such as large signal‐to‐noise ratio at low frequencies and high sensitivity at low applied field. The planar Hall resistance (PHR) curve in multilayer thin films with spinvalve structure has pre‐eminent sensitivity when compared to single layer and bilayer thin films. In this work, we report a model for PHR calculation that includes the behaviour of single domain basic structure in the external magnetic field. Our results show a qualitative dependence between PHR curves and the angle (β) between the exchange biased field direction and the easy axis of the free layer. As the β increases the sensitivity of the PHR curves also increases. Further, it is shown that our calculation helps to determine the exchange biased field direction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of seed layer on the sensitivity of exchange biased planar Hall sensor

We investigate systematically the effects of seed layer thickness on the sensitivity of exchange biased planar Hall sensors. The sensors consist of Ni 80Fe 20 ( t s)/Fe 50Mn 50 (20 nm)/Ni 80Fe 20 (20 nm) trilayers deposited on silicon substrates by sputtering, with t s varied from 0 nm to 50 nm. The sensors are linear near zero-field as a result of the pinning field from the Fe 50Mn 50 layer. We observed that the sensitivity and range of linearity of the sensors are strongly dependent on the Ni 80Fe 20 seed layer thickness. The sensitivity of the sensors were also calculated by taking into account the shunting effects of the various metal layers, and the values obtained agree well with the experimental values.

Novel Hall sensors developed for magnetic field imaging systems

We report here on the fabrication and application of novel planar Hall sensors based on shallow InGaP/AlGaAs/GaAs heterostructure with a two-dimensional electron gas (2DEG) as an active layer. The sensors are developed for two kinds of experiments. In the first one, magnetic samples are placed directly on the Hall sensor. Room temperature experiments of permalloy objects evaporated onto the sensor are presented. In the second experiment, the sensor scans close over a multigranular superconducting sample prepared on a YBCO thin film. Large-area and high-resolution scanning experiments were performed at 4.2 K with the Hall probe scanning system in a liquid helium flow cryostat.

Micromagnetic Simulation for nanobeads detection using planar Hall sensors

A micromagnetic simulation for the detection of magnetic nanobeads by planar Hall sensors is presented. The calculated dipole field created by the polarized nanobeads shows the strong dependence on the distance from beads to the sense plane. In this simulation, nonuniform dipole field, random configuration of beads, and experimental parameters of device were used. Micromagnetic calculation shows the linear signal response to the bead number. This linear behavior is insensitive to the random distribution of beads, but is sensitive to the bead number, indicating the possible application to quantitative biomolecular recognition.

Planar Hall sensors for micro-Hall magnetometry

In this work we present a new method to fabricate planar Hall sensors from GaAs–AlGaAs heterojunctions, which can be used to examine the local stray field at a specific section of a micron-sized magnet. Instead of mesa etching we implanted oxygen ions with an energy of 1.5 keV which deplete the two-dimensional electron gas underneath the exposed areas but leave the wafer flat. Planar double Hall cross devices were employed to investigate 30 nm thick electroplated Ni rings with outer and inner diameters ranging from 1.2 to 2 μm and from 0.3 to 1.6 μm, respectively. By comparing the signals from both Hall crosses of the sensor, we can distinguish between local stray field variations and changes of the global magnetization pattern. A hysteresis loop measured at a temperature of 110 K suggests that magnetization reversal occurs via a magnetic vortex structure.

Three-axis cryogenic Hall sensor

Magnetic field measurements are very important for magnetic and superconducting material research. Hall sensors have many advantages for these measurements. They can also be used for magnetic field profile measurements, which provide information about material homogeneity. We have developed a three-axis Hall system which consists of three perpendicular InSb Hall sensors for operation at room as well as cryogenic temperatures. The active area of each sensor is 50 × 50 μm2. It is located at the corner edge of the substrate and is suitable for detecting the spatial field profile within a cube of 225 × 225 × 225 μm3. The sensitivity of the sensor is of the order of 20 mV/T and the offset voltage is < 50 μV for a nominal control current of 10 mA. The problems of detecting the 3D field components using planar Hall sensors and the oscillatory signal behaviour due to quantum effects are discussed.