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Advances in micro- and nanotechnology have led to rapid employment of spintronic sensors in both recording and non-recording applications. These state-of-the-art magnetoresistive spintronic sensors exhibit high sensitivities and ultra-low field detectivities that meet requirements of smart sensing applications in the fields of internet of things, mobile devices, space technology, aeronautics, magnetic flux leakage, domotics, the environment, and healthcare. Moreover, their ability to be customized and miniaturized, ease of integration, and cost-effective nature make these sensors uniquely competitive with regard to mass production. In this study, we discuss magnetoresistive field sensors based on the planar-Hall effect, which are very promising for their high sensitivity and sensing ultra-low magnetic fields. We provide a detailed historical overview and discuss recent dramatic developments in several application fields. In addition, we discuss sensor material property requirements, design architectures, noise-reduction techniques, and sensing capabilities, along with the high repeatabilities and good flexibility characteristics of such devices. All of these high-performance characteristics apply across a wide temperature range and make the sensor robust when used in various novel applications. The sensor also appears promising because it is cost-effective and can be used in micro-sensing applications. Recently, a noteworthy study that combined integrated planar-Hall magnetoresistive sensors with microfluidic channels revealed their potential for highly localized magnetic field sensing. This characteristic makes them suitable for point-of-care-technologies that require resolutions of a few pT at room temperature. [ABSTRACT FROM AUTHOR]

The field sensitivity of a planar Hall effect (PHE) micro-ring type biosensor has been investigated as a function of magnetizing angle of the sensor material, for the sensing of low magnetic moment superparamagnetic labels. The field sensitivity is maximal at a magnetizing angle of α = 20°. At this optimized magnetizing angle, the field sensitivity of a PHE sensor is about 3.6 times higher than that measured at the conventional configuration, α = 90°. This optimization enables the PHE-ring sensor to detect superparamagnetic biolabels with ultra-low magnetic moments down to 4 × 10-13 emu. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We proposed a lightweight magnetizer toward the realization of a portable circumferential magnetic flux leakage (MFL) inspection tool for the detection of longitudinal defects with a linear motion between pipes and the inspection tool. The proposed magnetizer consists of four permanent magnetic poles constructing a configuration in which the like poles are separated by a θ angle ranging from 30° to 60° and the opposite poles are separated by a supplemental angle of θ. The distribution of the magnetic field generated by this magnetizer and caused by defects was studied by finite element methods as well as by experimental measurements. The results reveal that the new magnetizer has advantages of high amplitude and good uniformity of magnetic field over the state-of-the-art ones with configurations of two facing poles or quadrupole geometries. With the new magnetizer, the theoretical and experimental results show that the magnetization in the pipe increases slightly with the θ angle, but the uniformity of magnetization in the pipe and the magnetic field on the surface of pipe decrease dramatically with this angle. So, the optimum angle θ is proposed at around 30°–40°. The finite element calculation and the measurements of the MFL signal caused by artificial defects evidence the capabilities in detecting shallow longitudinal defects of the MFL inspection tool with our novel magnetizer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]