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Perpendicular magnetic tunnel junctions (p-MTJs) have been explored for spin transfer torque magnetic random access memory devices (STT-MRAMs). The current-induced switching (CIS) of the p-MTJs requires a relatively high current density (J); thereby, very thin insulating barriers are required, consequently increasing the risk of non-tunneling conduction mechanisms through the MgO film. In this work, we fabricated CoFeB/MgO/CoFeB p-MTJs and studied the CIS characteristics, with the obtained switching current densities of about 2 × 1010 A/m2. The filament conduction through the MgO film was induced by applying a high set current (Iset) until a significant decrease in the resistance (R) is observed. A decrease in R with increasing current (I) for parallel (P) and antiparallel (AP) states was observed. In contrast, an increase in R with the increasing I value was observed for filament p-MTJs. We used a two-channel model to extract the filament resistance (Rf) and filament current (If). The Rf dependence on the electrical power (Pf) was linearly fitted, and a heating coefficient β of about 6%/mW was obtained, which was much higher than 0.15%/mW obtained from the bulk metallic multilayers of the top electrode. The CIS for filament p-MTJs was modeled by considering the bias dependence of the tunneling and the thermal dependence of Rf, showing a significant change in the CIS curves and switching currents. Our study addresses the effect of filament conduction on the tunneling current of CoFeB/MgO/CoFeB p-MTJs, critical for the design and control of the p-MTJ based devices, such as STT-MRAMs. [ABSTRACT FROM AUTHOR]

Unshielded spin-valve sensors (6×2 μm[sup 2]) with both synthetic ferrimagnet free (SF) and synthetic antiferromagnet pinned (SAF) layers are demonstrated, exhibiting high sensitivities, good thermal stability and reduced free layer effective magnetic thickness (t[sub eff]). The free layer t[sub eff] can be reduced to ∼10 Å while maintaining its physical thickness near 60 Å, without significant magnetoresistive signal loss (MR∼6%). After current biasing, the sensors show a linearized response, demonstrating a coherent switching of the synthetic free layer. Sensor sensitivity (S) increases with decreasing free layer effective magnetic thickness (Sapprox. 0.5%/Oe at t[sub eff]=10 Å) as expected from the decrease of the free layer demagnetizing field. The coupling field (H[sub f]) between the free and pinned layers increases with decreasing t[sub eff] (H[sub f]∝M[sub s][sup 2]/(t[sub eff]M[sub eff][sup f])). The sensors are thermally stable upon anneals up to 300 °C. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness, oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance (TMR) ratio of optimal MTJs is over 60% at annealing temperature 385°C. The (001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340°C. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film. [ABSTRACT FROM AUTHOR]

Presents a study where the changes in the tunnel magnetoresistance (TMR) values with annealing temperatures were observed to be associated with changes in barrier parameters. Overview of tunnel junction random access memories; Estimated head parameters for 100 gigabit.

Presents information on a study which reported the elaboration by ion beam deposition (IBD) of manganese-iridium-biased spin valves. Advantages of the IBD technique over other physical deposition methods; Experimental considerations; Characterization of the spin valve layer materials in terms of composition and resistivity; Discussion on the thermal stability of the spin valves; Conclusion.

Presents information on a study which tested the fabricated dual-stripe giant magnetoresistive (GMR) devices with an insulating spacer on tape media. Dual stripe GMR sensor fabrication; Head design and process description; Tape head fabrication; GMR elements transfer curves in static field; Head tests on tape; Tape head results; Conclusion.

Presents information on a study which described shielded spin-valve tape heads with permanent magnet stabilization. Head design and fabrication; Head performance on tape; Conclusions.

Describes the structure of Manganese-Rh (MnRh) exchange layer which has a good corrosion resistance and good exchange coupling. Structure of the spin valve; Study of the corrosion resistance of the exchange material; Results and analysis of the study.

Current perpendicular to the plane read-head elements suitable for high-density magnetic storage require low resistance while maintaining a reasonable magnetoresistive (MR) signal (R×A<1 Ω μm2 and MR>20% for areal densities >200 Gb/in2). This letter shows that competitive low R×A junctions can be produced using underoxidized barriers starting from 0.9 nm thick Al layers. For as-deposited junctions, tunneling magnetoresistance (TMR) ∼20% for R×A∼2–15 Ω μm2 is obtained, while in the R×A∼60–150 Ω μm2 range, TMR values between 40% to 45% are achieved. A limited number of junctions exhibits considerably lower R×A values with respect to the average, while keeping a similar MR (down to 0.44 Ω μm2 with TMR of 20% and down to 2.2 Ω μm2 with TMR of 52%). Experimental data suggest that current confinement to small regions (barrier defects/hot spots) may explain these results. [ABSTRACT FROM AUTHOR]

Presents information on a study that investigated the effect of ion milling process parameters used to pattern the magnetic elements. Methodology of the study; Results and discussion on the study; Conclusions.

Presents a study where spin dependent tunnel junctions aimed for storage element in magnetic random access memory (MRAM) cells were switched between low and high resistance states using 20 nanosecond current pulses on two perpendicular conductors. Experimental method; Results and discussion; Conclusion.

Presents information on a study which showed successful vertical integration of magnetic tunneling junctions with hydrogenated amorphous silicon diodes. Experimental methods; Results and discussion; Conclusions.

Details the use of a micromagnetic model to study the dual-stripe giant magneto-resistive (GMR) tape head (DSGMR) operation. Elements of the micromagnetic model; DSGMR and Dual-GMR simulation.

Proposes a head design and wafer level testing of nickel iron copper (NiFe/Cu)xn dual stripe giant magnetoresistive (DS-GMR) sensors. Calculated dibit response of a DS-GMR head with head and media parameters; Wafer level response of the bottom and top GMR elements on the fabricated DS-GMR sensor.

In conventional communications systems, information is transmitted by modulating the frequency, amplitude or phase of the carrier signal, which often occurs in a binary fashion over a very narrow bandwidth. Recently, ultra-wideband signal transmission has gained interest for local communications in technologies such as autonomous local sensor networks and on-chip communications, which presents a challenge for conventional electronics. Spin-torque nano-oscillators (STNOs) have been studied as a potentially low power highly tunable frequency source, and in this report we expand on this to show how a specific dynamic phase present in vortex-based STNOs makes them also well suited as Wideband Analogue Dynamic Sensors (WADS). This multi-functionality of the STNOs is the basis of a new modulation and demodulation scheme, where nominally identical devices can be used to transmit information in both a digital or analogue manner, with the potential to allow the highly efficient transmittance of data. [ABSTRACT FROM AUTHOR]

Herein, A microfluidic device is described, produced with a 3D-printed master mould that rapidly separates and concentrates Escherichia coli directly from whole blood samples, enabling a reduction in the turnaround time of bloodstream infections (BSIs) diagnosis. Moreover, it promotes the cleansing of the blood samples whose complexity frequently hampers bacterial detection. The device comprises a serpentine mixing channel with two inlets, one for blood samples (spiked with bacteria) and the other for magnetic nanoparticles (MNPs) functionalized with a (bacterio)phage receptor-binding protein (RBP) with high specificity for E. coli. After the magnetic labelling of bacteria throughout the serpentine, the microchannel ends with a trapping reservoir where bacteria-MNPs conjugates are concentrated using a permanent magnet. The optimized sample preparation device successfully recovered E. coli (on average, 66%) from tenfold diluted blood spiked within a wide range of bacterial load (102 CFU to 107 CFU mL−1). The non-specific trapping, tested with Staphylococcus aureus, was at a negligible level of 12%. The assay was performed in 30 min directly from diluted blood thus presenting an advantage over the conventional enrichment in blood cultures (BCs). The device is simple and cheap to fabricate and can be tailored for multiple bacterial separation from complex clinical samples by using RBPs targeting different species. Moreover, the possibility to integrate a biosensing element to detect bacteria on-site can provide a reliable, fast, and cost-effective point-of-care device. [ABSTRACT FROM AUTHOR]

Industrial requirements are continuously pushing the sensor limits toward higher signal-to-noise ratio under harsh environments, without compromising production costs by additional electronics. Non-full resistive Wheatstone bridge architectures arise as a compact and cheaper alternative to full-bridge measurement schemes, despite a lower output, linearity, and immunity to thermal drifts promoted by the replacement of the out-of-phase sensing elements by passive elements. However, the combination of state-of-the-art magnetoresistive (MR) sensors with thermally compatible materials used as tunable thin-film resistor at wafer level can lead to competitive prototypes for applications with high constraints. Therefore, the resistivity and the temperature coefficient of resistance (TCR) of Cr, Ti, and TiW thin films were evaluated as potential candidates for a thermal and electrical stable non-full MR bridge. Within a TCR around 1059 ± 12 ppm/°C for a spin-valve sensor lying between the values observed for a Ti thickness range of 300 Å up to 500 Å (571.9 ± 8.3 and 1347 ± 69 ppm/°C, respectively), a sin/cos magnetic encoder was prototyped in a non-full-bridge architecture with a thermal offset drift of 51.48 ± 0.25 nV/Vcc/°C and an offset voltage of 16 mV/Vcc. [ABSTRACT FROM AUTHOR]

This article presents experimental investigations of exchange-biased Permalloy planar Hall effect sensor crosses with a fixed active area of w×w=40×40 μm2 and Permalloy thicknesses of t=20, 30, and 50 nm. It is shown that a single domain model describes the system well and that the thicker film will have a higher signal as well as a lower noise. It is estimated that the signal-to-noise ratio for bead detection increases by a factor 2.1 when t is increased from 20 to 50 nm and hence a higher t is beneficial for biosensor applications. This is exemplified with calculations on M-280 Dynabeads®. [ABSTRACT FROM AUTHOR]

Tuberculosis is one of the major public health concerns. This highly contagious disease affects more than 10.4 million people, being a leading cause of morbidity by infection. Tuberculosis is diagnosed at the point-of-care by the Ziehl-Neelsen sputum smear microscopy test. Ziehl-Neelsen is laborious, prone to human error and infection risk, with a limit of detection of 10 4 cells/mL. In resource-poor nations , a more practical test, with lower detection limit, is paramount. This work uses a magnetoresistive biosensor to detect BCG bacteria for tuberculosis diagnosis. Herein we report: i) nanoparticle assembly method and specificity for tuberculosis detection; ii) demonstration of proportionality between BCG cell concentration and magnetoresistive voltage signal; iii) application of multiplicative signal correction for systematic effects removal; iv) investigation of calibration effectiveness using chemometrics methods; and v) comparison with state-of-the-art point-of-care tuberculosis biosensors. Results present a clear correspondence between voltage signal and cell concentration. Multiplicative signal correction removes baseline shifts within and between biochip sensors, allowing accurate and precise voltage signal between different biochips. The corrected signal was used for multivariate regression models, which significantly decreased the calibration standard error from 0.50 to 0.03 log 10 (cells/mL). Results show that Ziehl-Neelsen detection limits and below are achievable with the magnetoresistive biochip, when pre-processing and chemometrics are used. [ABSTRACT FROM AUTHOR]

Directed cell migration is essential for many biological processes, such as embryonic development or cancer progression. Cell contractility and adhesion to the extracellular matrix are known to regulate cell locomotion machinery. However, the cross-talk between extrinsic and intrinsic factors at the molecular level on the biophysical mechanism of three dimensional (3D)-directed cell migration is still unclear. In this work, a novel physiologically relevant in vitro model of the extracellular microenvironment is used to reveal how the topological anisotropy of the extracellular matrix synergizes with actomyosin contractility to modulate directional cell migration morphodynamics. This study shows that cells seeded on polarized 3D matrices display asymmetric protrusion morphodynamics and in-vivo-like phenotypes. It is found that matrix anisotropy significantly enhances cell directionality, but strikingly, not the invasion distance of cells. In Rho-inhibited cells, matrix anisotropy counteracts the lack of actomyosin-driven forces to stabilize cell directionality suggesting a myosin-II-independent mechanism for cell guidance. Finally, this study shows that on isotropic 3D environments, cell directionality is independent of actomyosin contractility. Altogether, this study provides novel quantitative data on the biomechanical regulation of directional cell motion and shows the important regulatory role of matrix anisotropy and actomyosin forces to guide cell migration in 3D microenvironments. [ABSTRACT FROM AUTHOR]

The synchronisation of magnetic tunnel junctions in the high frequency domain has attracted significant interest in the context of novel computation paradigms, specifically neuromorphic spintronics and probabilistic computing. In this work, a design for the coupling and synchronization of spin torque vortex oscillators (STVOs) is implemented. The geometry comprises the fabrication of adjacent pairs of STVO nanopillars (MgO-based magnetic tunnel junctions), with an edge-to-edge distance down to 100 nm, together with individual top contacts that allow an independent electrical access to each device. In this geometry, the magneto-dipolar coupling promotes the synchronization of the two oscillators, at the same time as the access to the frequency and phase of each individual oscillator is possible. Both frequency and time domain measurements confirm a successful synchronization, with the coupling being controlled by the relative DC bias in each oscillator. As a proof-of-concept towards an oscillator-based Ising machine, it is also shown that the second harmonic injection locking of an STVO can be controlled by tuning the magneto-dipolar coupling to its correspondent STVO pair. These results represent a step forward for the implementation of magneto-dipolar coupled magnetic tunnel junctions, specifically in the field of unconventional computing hardware. Spin torque nano-oscillators (STNOs) have been proposed as the building blocks of Ising machines for solving combinatorial optimization problems. In this study, the authors experimentally demonstrate how the short-range magnetic coupling between a pair of STNOs controls their ability to lock with an external second harmonic signal. [ABSTRACT FROM AUTHOR]

The sensitivity of tunneling magnetoresistance sensors is an important performance parameter. It depends on the derivative of resistance versus magnetic field (transfer curve) and the current and is expressed as the product of the two factors. Previous research has demonstrated that the bias voltage has a significant impact on the sensitivity. However, no research has been conducted into the dependence of current and the derivative on bias voltage magnitude and polarity, and their contribution to the sensitivity. Thus, this paper investigates the dependence of sensitivity, derivative of resistance versus magnetic field curve and current on bias voltage magnitude and polarity in CoFeB/MgO/CoFeB-based tunneling magnetoresistance sensors with weak, strong and no voltage-controlled perpendicular magnetic anisotropy modification. It demonstrates that the sensitivity dependence on bias voltage for sensors with voltage controlled magnetic anisotropy modification showed no saturation up to 1 V. Moreover, the sensitivity asymmetry with respect to bias polarity changed significantly with bias, reaching a ratio of 6.7. Importantly, the contribution of current and the derivative of resistance versus magnetic field curve to the sensitivity showed a crossover. The current dominated the bias dependence of sensitivity below the crossover voltage and the derivative above the voltage. Furthermore, the crossover voltage in sensors without voltage controlled magnetic anisotropy modification did not depend on polarity, whereas in sensors with voltage controlled magnetic anisotropy modification, it appeared at significantly higher voltage under positive than negative polarity. [ABSTRACT FROM AUTHOR]

The potato cyst nematode (PCN), Globodera pallida, has acquired significant importance throughout Europe due to its widespread prevalence and negative effects on potato production. Thus, rapid and reliable diagnosis of PCN is critical during surveillance programs and for the implementation of control measures. The development of innovative technologies to overcome the limitations of current methodologies in achieving early detection is needed. Lab-on-a-chip devices can swiftly and accurately detect the presence of certain nucleotide sequences with high sensitivity and convert the presence of biological components into an understandable electrical signal by combining biosensors with microfluidics-based biochemical analysis. In this study, a specific DNA-probe sequence and PCR primers were designed to be used in a magnetoresistive biosensing platform to amplify the internal transcribed spacer region of the ribosomal DNA of G. pallida. Magnetic nanoparticles were used as the labelling agents of asymmetric PCR product through biotin–streptavidin interaction. Upon target hybridization to sensor immobilized oligo probes, the fringe field created by the magnetic nanoparticles produces a variation in the sensor's electrical resistance. The detection signal corresponds to the concentration of target molecules present in the sample. The results demonstrate the suitability of the magnetic biosensor to detect PCR target product and the specificity of the probe, which consistently distinguishes G. pallida (DV/V > 1%) from other cyst nematodes (DV/V < 1%), even when DNA mixtures were tested at different concentrations. This shows the magnetic biosensor's potential as a bioanalytical device for field applications and border phytosanitary inspections. [ABSTRACT FROM AUTHOR]

The article offers information about integrated spintronic biochip platforms. The topic was discussed by Paulo P. Freitas, considered as one of the Institute of Electrical and Electronic Engineers (IEEE) Magnetic Society Distinguished Lecturers for 2008. He claims that these platforms consist of a microfluidic unit, an arraying and detector chip, and electronic control and readout boards. They are being developed for portable, point-of-care, diagnostic applications.

Information encoding in barcodes using magnetic-based technology is a unique strategy to read data buried underneath non-transparent surfaces since a direct line-of-sight between the code and the reader is not required. This technology is of particular interest in secure labeling and recyclable packaging applications. However, current magnetic reading heads, such as those employed for magnetic ink character recognition (MICR), need to be placed in contact with the magnetic structures, limiting the depths at which the information can be read. This article describes a strategy to overcome that limitation by replacing the traditional inductive heads with tunnel magnetoresistive (TMR) sensors. Soft-magnetic codes can be printed using conventional LaserJet toners and, by having their magnetization set with a permanent magnet (PM) included in the device, the resulting magnetic field can be read using a TMR sensor. We demonstrate that such a device can read barcodes at depths of at least 1 mm. It can also resolve individual structures as thin as $200 ~\mu \text{m}$ when used in contact. [ABSTRACT FROM AUTHOR]

The present paper describes a compact point of care (POC) optical device for therapeutic drug monitoring (TDM). The core of the device is a disposable plastic chip where an immunoassay for the determination of immunosuppressants takes place. The chip is designed in order to have ten parallel microchannels allowing the simultaneous detection of more than one analyte with replicate measurements. The device is equipped with a microfluidic system, which provides sample mixing with the necessary chemicals and pumping samples, reagents and buffers into the measurement chip, and with integrated thin film amorphous silicon photodiodes for the fluorescence detection. Submicrometric fluorescent magnetic particles are used as support in the immunoassay in order to improve the efficiency of the assay. In particular, the magnetic feature is used to concentrate the antibody onto the sensing layer leading to a much faster implementation of the assay, while the fluorescent feature is used to increase the optical signal leading to a larger optical dynamic change and consequently a better sensitivity and a lower limit of detection. The design and development of the whole integrated optical device are here illustrated. In addition, detection of mycophenolic acid and cyclosporine A in spiked solutions and in microdialysate samples from patient blood with the implemented device are reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel molecularly imprinted photonic polymer for optical detection of C-reactive protein (CRP). • Fabrication of one-dimensional reflective grating patterned PDMS substrate by soft lithography. • Sensor response sensitive and selective to CRP assayed in spiked human serum. • Label-free optical method to analyze circulating protein biomarkers related to inflammatory bowel diseases. This work presents the development of a novel photonic-based sensor on a nanoscale patterned polydimethylsiloxane (PDMS) substrate acting as transducer, combined with a molecularly imprinted polymer for the rapid and sensitive detection of C-reactive protein (CRP). A silicon wafer was patterned using electron-beam lithography with a one-dimensional (1D) reflective grating (periodicity of about 400 nm) and then replicated using nanoimprint lithography. The latter silicon mould was used for replica moulding to generate a patterned PDMS. The unique 1D design gave PDMS photonic properties that were suitable as a substrate to assemble the biorecognition layer. The surface of the photonic PDMS was modified to become hydrophilic and additionally functionalized with vinyl silane groups to bind the imprinted polymer, resulting in a photonic molecularly imprinted polymer substrate (PMIPS). The developed method was successfully used to detect CRP in serum samples. The reflectance intensity decreased with increasing CRP concentrations, and the sensing PMIPS showed a linear response between 0.005 and 1.215 µg mL−1, a limit of detection of 0.003 µg mL−1, and a selective response to CRP when tested against serum calprotectin. Overall, this novel optical sensor can be used to detect CRP, a serum biomarker of inflammation, particularly in inflammatory bowel diseases. [ABSTRACT FROM AUTHOR]

Full Wheatstone Bridge incorporating a serially connected ensemble of Magnetic tunnel junctions was produced, targeting an application as a magnetic field compass. To that end, MTJs with RxA\sim 10\ k\Omega\ \mum^2, TMR\sim 150–200%, Hf=5\ Oe and Hf=5\ Oe were produced. In order to achieve a full bridge signal, two stacks with an asymmetric SAF reference structure where used to produce MTJs with opposite dR/dH upon annealing in the same substrate. The resulting Bridges exhibit sensitivities between 13.5–32 mV/V/Oe depending on the field range and provide a significantly advantageous alternative to AMR and GMR based bridges. [ABSTRACT FROM PUBLISHER]

Over the past five years, magnetoelectronics has emerged as a promising new platform technology for biosensor and biochip development. The techniques are based on the detection of the magnetic fringe field of a magnetically labeled biomolecule interacting with a complementary biomolecule bound to a magnetic-field sensor. Magnetoresistive-based sensors, conventionally used as read heads in hard disk drives, have been used in combination with biologically functionalized magnetic labels to demonstrate the detection of molecular recognition. Real-world bio-applications are now being investigated, enabling tailored device design, based on sensor and label characteristics. This detection platform provides a robust, inexpensive sensing technique with high sensitivity and considerable scope for quantitative signal data, enabling magnetoresistive biochips to meet specific diagnostic needs that are not met by existing technologies. [Copyright &y& Elsevier]

In this work, a new mechanism to combine a non-volatile behaviour with the spin diode detection of a vortex-based spin torque nano-oscillator (STVO) is presented. Experimentally, it is observed that the spin diode response of the oscillator depends on the vortex chirality. Consequently, fixing the frequency of the incoming signal and switching the vortex chirality results in a different rectified voltage. In this way, the chirality can be deterministically controlled via the application of electrical signals injected locally in the device, resulting in a non-volatile control of the output voltage for a given input frequency. Micromagnetic simulations corroborate the experimental results and show the main contribution of the Oersted field created by the input RF current density in defining two distinct spin diode detections for different chiralities. By using two non-identical STVOs, we show how these devices can be used as programmable non-volatile synapses in artificial neural networks. [ABSTRACT FROM AUTHOR]

NiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz. In this report, we present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz). This is achieved via micromagnetic simulations and electrical characterisation in magnetic tunnel junctions, both directly via the spin-diode effect and indirectly via the measurement of the coupling with the gyrotropic critical current. The excitation mechanism and spatial profile of the modes are shown to have a complex dependence on the vortex core position. Additionally, the inter-mode coupling between the fundamental gyrotropic mode and the higher order modes is shown to reduce or enhance the effective damping depending upon the sense of propagation of the confined spin wave. The control and manipulation of spin waves holds promise for miniaturized radio-frequency spintronic devices. The authors demonstrate electrical access to the dynamics of magnetic vortices in confined geometries: a new avenue of research for future applications exploiting super high frequency behaviour for microwave communications and computing applications. [ABSTRACT FROM AUTHOR]

Spin torque nano-oscillators (STNOs) have been shown to efficiently "lock" to electrical signals whether these are from external sources, self-reflected signals, or other STNOs via mutual synchronization. Traditionally, the locked state of an STNO has been considered digital, either "ON" or "OFF." In this report, we show how the phase in the locked state can vary significantly as a function of the applied dc to the STNO with the phase strongly affecting the emitted power. This phase dependence demonstrates the analogue nature of the locked state, offering an extra degree of freedom when designing STNO-based neural networks. [ABSTRACT FROM AUTHOR]

Industrial sensor applications rely on the implementation of full Wheatstone bridge architectures, demanding the development of low-cost and mass production methods of magnetic tunnel junctions (MTJ) based on CoFeB/MgO/CoFeB. In particular, monolithic bridge microfabrication has been demonstrated through the double deposition of MTJ stacks engineered by asymmetric reference layers with non-evenly layered synthetic antiferromagnet (SAF) structures. However, extending the standard double magnetic layered SAF into a triple magnetic multilayer system brings critical changes in the overall performance of the reference structure, which directly influences the magnetic stability of the device. Consequently, a theoretical model of a triple magnetic layered AF/SAF structure was developed to support the understanding of the magnetic response of the reference layers, aiming to improve the magnetic stability around zero field. A full MTJ Wheatstone bridge incorporating the optimized double and triple reference structures was microfabricated with a linear and hysteresis-free response. Furthermore, a high thermal endurance of both structures was verified through the measurement of the magnetotransport behavior of each type of MTJ structure within a reversible magnetic field range of ±2 kOe and a temperature sweep from room temperature up to 200 °C. [ABSTRACT FROM AUTHOR]

A new device architecture using giant magnetoresistive sensors demonstrates the capability to detect very low magnetic fields on the pT range. A combination of vertically packed spin-valve sensors with two-dimensional in-plane arrays, connected in series and in parallel, delivers a final detection level of 360 pT/ Hz at 10 Hz at room temperature. The device design is supported by an analytical model developed for a vertically packed spin-valve system, which takes into account all magnetic couplings present. Optimization concerning the spacer thickness and sensor physical dimensions depending on the number of pilled up spin-valves is necessary. To push the limits of detection, arrays of a large number of sensing elements (up to 440,000) are patterned with a geometry that improves sensitivity and in a configuration that reduces the resistance, leading to a lower noise level. The final device performance with pT detectivity is demonstrated in an un-shielded environment suitable for detection of bio-signals. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) incorporating GeSbTe thermal barriers and weakly pinned free layers (Hex ∼ 60 Oe) have been produced with areas between 1 × 1 μm² and 3 × 8μm². Current pulses lasting from 100 μs down to 20 ns were used to heat the MTJs and reverse the free layer pinning field. It is demonstrated that pulses with 7 mW/μm² can be used to switch the free layer of MTJs incorporating GeSbTe (20 mW/μm² without GeSbTe). The dependence of the power required to switch the MTJs is studied with respect to sample area, pulse duration, and GeSbTe thickness. [ABSTRACT FROM AUTHOR]

We present an investigation into the in-plane field induced free layer state transitions found in magnetic tunnel junctions. By applying an ac current into an integrated field antenna, the magnetisation of the free layer can be switched between the magnetic vortex state and the quasi-uniform anti-parallel state. When in the magnetic vortex state, the vortex core gyrates a discrete number of times, and at certain frequencies there is a 50% chance of the core gyrating n or n − 1 times, leading to the proposal of a novel nanoscale continuous digital true random bit generator. [ABSTRACT FROM AUTHOR]

In this paper, junctions with reduced Hf coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (111) texture that can be the origin of lower Hf and coercivity when compared, with CoFe. Junctions processed down to 2 × 4 μm² with 40-Å-thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R × A ∼ 400 Ω·μm²), Hc of ∼10 Oe and Hf of ∼2 Oe. CoFe-based junctions (R × A ∼ 500 Ω·μm²) have lower TMR (∼35%) and larger Hf (∼5-6 Oe) and Hc (∼12-14 Oe). Local chemical. composition analysis of the cross section indicated Fe-O segregation with very little Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones. [ABSTRACT FROM AUTHOR]

The effect of the kinetic parameters of an assistance ion beam on the crystallization of ion beam deposited MgO was investigated. It is shown that the crystallization of MgO in the as-deposited state is strongly dependent on the assistance beam parameters. Furthermore, two deposition regimes corresponding to different ranges of the assistance beam energy are found. XRD and TEM studies of CoFeB/MgO/CoFeB with MgO deposited in the two regimes show that CoFeB crystallization is favored when low energy assist beams are used, despite no differences being found in the MgO. [ABSTRACT FROM AUTHOR]

Presents a study which conducted a quasi-static and dynamic analysis of spin valve magnetic tape heads with synthetic free and pinned layers versus heads with a conventional free layer and a synthetic pinned layer. Head design and fabrication; Head performance.

Presents information on a study which measured on chip the vibration of microelectromechanical systems microbridges excited by direct current and alternating current voltages using spin-valve sensors. Methods; Results; Discussion.

This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/ $\sqrt{\text{Hz}}$ at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm $^2$. NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions. [ABSTRACT FROM AUTHOR]

The magnetization orientation of the polarizing reference layer would fluctuate between the parallel and antiparallel states when the reference layer loses stability. In this paper, a combined analytical and simulation study is presented to predict the magnetic dynamics of the spin valve element with single-domain magnets as the free and reference layers. We acquire a complete phase diagram that includes the normal spin-torque switching and random magnetization fluctuations by tuning the spin torque strength between the free and reference layers. The phase dynamics strongly depends on the magnetization state of the reference layer, showing that the instability of the reference layer could be responsible for the random fluctuation events. [ABSTRACT FROM AUTHOR]

The magnetic domain configuration and the magnetization reversal behavior of micropatterned exchange bias elements were investigated by means of magnetic force microscopy. In addition to the unidirectional anisotropy the shape anisotropy determines the overall magnetization reversal behavior. In order to modify the ratio between both anisotropy contributions, the exchange bias field strength was reduced by means of 5 keV He+ ion irradiation. For the as-prepared samples, a monodomain magnetization state with the magnetization direction aligned along the exchange bias field direction was found regardless of the element shape. After irradiation the unidirectional anisotropy contribution is reduced and hence the previously homogeneous magnetization state breaks up into small domains with 360° domain walls in between. The appearance of these domain walls, which was mainly observed for the descending branch of the magnetization reversal, is found to depend strongly on the structure width and orientation. [ABSTRACT FROM AUTHOR]

Precision healthcare brings many technological challenges for the development of new tools. Among these, the detection of biomagnetic fields in the pico-Tesla range, at room temperature, requires the state-of-the-art sensors with high signal-to-noise ratio. Also, given that biomedical signals are characterized by their low frequency, minimizing the sensor noise has to be addressed simultaneously with the efforts to increase sensor sensitivity. In this paper, we maximize the spin-valve sensors sensitivity by optimizing the distance between the poles of double-layer magnetic flux concentrators (MFCs). An enhancement of the sensitivity from 1.5%/mT (3.8 mV/mT) to 654%/mT (1765 mV/mT) could be observed for a double-layer architecture when a distance from the recessed steep CoZrNb MFC to the NiFe pole is $100~\mu \text{m}$. The impact on the detectivity was evaluated through noise enabling the detection of magnetic fields of 322 pT/Hz1/2 at 10 Hz. [ABSTRACT FROM AUTHOR]

Abstract The excellent electronic properties of single-layer graphene provide the fundamental basis for its use in advanced electronics applications. Graphene-based biosensors, however, are one of the exceptions among the applications that take advantage of the unique properties of this material, because high hydrophobicity of graphene hinders the controlled immobilization of biomolecular probes, particularly of antibodies for immunoassays. In contrast to methods that rely on aggressive chemical oxidation of graphene, we overcome this challenge by implementing an effective strategy that modifies single-layer graphene to render it hydrophilic and biocompatible without compromising the electronic structure. Graphene produced in-house by chemical vapor deposition (CVD) was modified with a heterobifunctional linker that attached to the surface via a pyrene group and presented a standard N-hydroxysuccinimide (NHS) ester ligand for covalent immobilization of biomolecules. The suitability of thus modified surface for biofunctionalization was then confirmed via real-time monitoring of the immobilization of an antibody by quartz crystal microbalance (QCM) measurements followed by the chemical characterization by x-ray photoelectron spectroscopy (XPS). Finally, as a proof-of-concept for biofunctionalization of graphene without compromising its electronic structure, a graphene immuno-field-effect transistor (immuno-FET) was fabricated, biofunctionalized, and tested for detection of Matrix Metalloproteinase 9 (MMP-9), a biomarker related to clinical diagnostics of ischemic stroke. Graphical abstract Unlabelled Image Highlights • Biofunctionalize graphene to exploit unique electronic properties in biosensing • Systematically characterize each functionalization step by complementary techniques • Heterobifunctional linker between hydrophobic graphene surface and antibodies • Blocking strategy to minimize nonspecific adsorption after biofunctionalization • Biofunctionalized graphene EGFET for proof-of-principle biorecognition measurements [ABSTRACT FROM AUTHOR]

Highlights • Thermal stability of H ex for MnPt and MnIr was studied in AF/FM bilayers and TMR stacks. • A model was developed to describe the H ex and H c behaviors at high temperatures. • A better thermal stability was observed in TMR stacks than bilayers. Abstract Ensuring a reliable reference in magnetoresistive devices requires robust exchange biased antiferromagnetic/ferromagnetic (AF/FM) bilayers with strong resilience to high temperatures. In this work, we studied the thermal stability of MnPt and MnIr by investigating the exchange bias effect in AF/CoFe bilayers and tunneling magnetoresistance (TMR) full stacks. In bilayers, the obtained blocking temperature ( T b ) of 380 °C for MnPt is higher than T b of 340 °C for MnIr, indicating a better thermal stability. Based on Malozemoff's model, we developed a comprehensive model to describe the exchange bias field ( H ex ) behavior at high temperature by considering the T b distribution and temperature dependence of FM magnetization, giving a good agreement with the experimental data. With increasing temperature, a coercivity ( H c ) enhancement peak was observed in MnIr bilayer, which shows a good agreement with T b distribution. This evidences the H c peak is dominated by the thermal activation of AF grains, indicating that the H c peak only appears at T b center , which is lower than overall T b . The structural properties and grain size of AF layers were studied by X-ray diffraction (XRD), where a mean grain size of 10.6 and 12.6 nm were obtained for MnPt and MnIr, respectively. Compared to bilayers, a more stable thermal behavior was observed in full stacks. In conclusions, our study compared the thermal stability of exchange bias coupling using MnPt and MnIr and developed a comprehensive model to study their temperature dependence. This proposed approach can be used for theoretical studies and experimental designs of AF-based materials for spintronic applications, such as magnetoresistive devices and high density memories. [ABSTRACT FROM AUTHOR]

Highlights • We study annealing effect on memory states stability in CoFeB/MgO/CoFeB based perpendicular MTJs. • Our study indicates a ferromagnetic coupling between the storage and reference layers. • Enhance pMTJs stability by playing perpendicular magnetic anisotropy and interlayer coupling. Abstract Perpendicular magnetic tunnel junctions (p-MTJs) attract great interest because of their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). The annealing process is critical to achieve the required structural and magnetic properties, therefore obtaining high perpendicular tunneling magnetoresistance (p-TMR) and lower switching current. In this work, the CoFeB/MgO/CoFeB-based p-TMR stack was prepared and a high p-TMR value of 155.9% was obtained from CIPT. The p-MTJs were patterned with pillar sizes ranging from 50 nm to 1000 nm and were annealed upon different annealing temperatures (T A) of 300 and 340 °C. The resistance at parallel (R P) and antiparallel (R AP) state in p-MTJs was obtained upon the application of a ±30 mT perpendicular magnetic field, where the angle of magnetization between storage and reference layer at memory state, θ P and θ AP , were derived from the P and AP resistance ratios with and without magnetic field. The condition θ P = θ AP of about 63.5° was found in as-deposited samples, indicating a ferromagnetic interlayer coupling between storage and reference layers, where θ P = 0° and θ AP = 180° at T A = 300 °C and 340 °C demonstrate a stable memory state. The stability of the resistance state was modeled by considering the evolution of effective perpendicular magnetic anisotropy (K eff) and interlayer coupling constant (J), showing a method to evaluate the ratio of K eff / J via the memory state resistance characterization, where the K eff / J of about −1.26 was obtained in our as-deposited samples. Our study assesses the effect of T A on the θ P and θ AP and supplies the method to enhance the stability through the optimization of perpendicular magnetic anisotropy and interlayer coupling, so to better control the performance of p-MTJ-based STT-MRAMs. [ABSTRACT FROM AUTHOR]

Magnetoresistive (MR) sensors have been identified as promising candidates for the development of high-performance magnetometers due to their high sensitivity, low cost, low power consumption, and small size. The rapid advance of MR sensor technology has opened up a variety of MR sensor applications. These applications are in different areas that require MR sensors with different properties. Future MR sensor development in each of these areas requires an overview and a strategic guide. An MR sensor roadmap (non-recording applications) was therefore developed and made public by the Technical Committee of the IEEE Magnetics Society with the aim to provide an research and development (R&D) guide for MR sensors intended to be used by industry, government, and academia. The roadmap was developed over a three-year period and coordinated by an international effort of 22 taskforce members from ten countries and 17 organizations, including universities, research institutes, and sensor companies. In this paper, the current status of MR sensors for non-recording applications was identified by analyzing the patent and publication statistics. As a result, timescales for MR sensor development were established and critical milestones for sensor parameters were extracted in order to gain insight into potential MR sensor applications (non-recording). Five application areas were identified, and five MR sensor roadmaps were established. These include biomedical applications, flexible electronics, position sensing and human–computer interactions, non-destructive evaluation and monitoring, and navigation and transportation. Each roadmap was analyzed using a logistic growth model, and new opportunities were predicted based on the extrapolated curve, forecast milestones, and professional judgment of the taskforce members. This paper provides a framework for MR sensor technology (non-recording applications) to be used for public and private R&D planning, in order to provide guidance into likely MR sensor applications, products, and services expected in the next 15 years and beyond. [ABSTRACT FROM AUTHOR]

The growing need for biological information at the single cell level has driven the development of improved cytometry technologies. Flow cytometry is a particularly powerful method that has evolved over the past few decades. Flow cytometers have become essential instruments in biomedical research and routine clinical tests for disease diagnosis, prognosis, and treatment monitoring. However, the increasing number of cellular parameters unveiled by genomic, proteomic, and metabolomic data platforms demands an augmented multiplexability. Also, the need for identification and quantification of relevant biomarkers at low levels requires outstanding analytical sensitivity and reliability. In addition, growing awareness of the advantages associated with miniaturization of analytical devices is pushing forward the progress in integrated and compact, microfluidic-based devices at the point-of-care. In this context, novel types of flow cytometers are emerging during the search to tackle these challenges. Notwithstanding the relevance of other promising alternatives to standard optical flow cytometry (e.g., mass cytometry, various optical and electrical microcytometers), this report focuses on a recent microcytometric technology based on magnetic sensors and magnetic particles integrated into microfluidic structures for dynamic bioanalysis of fluid samples—magnetic flow cytometry. Its concept, main developments, targeted applications, as well as the challenges and trends behind this technology are presented and discussed. Graphical abstract ᅟ "Kindly advise whether there is online abstract figure for this paper. If so, kindly resupply.The graphical abstract is correctly supplied. [ABSTRACT FROM AUTHOR]

We report the design and characterization of a lateral and vertical hydrodynamic focusing feature for whole cell detection on a miniaturized flow cytometer. The developed system, based on magnetic sensing, incorporates spin valve sensors on the bottom of the microfluidic channels that detect cells labeled with magnetic beads. An adaptable 3D hydrodynamic focusing system was developed that pushes labeled cells towards the bottom of the microchannel, closer to the sensors, allowing increased signal amplitude for cells labeled with magnetic beads and enhanced discrimination of labeled cells. Fluorescence microscopy indicates that the lateral and vertical hydrodynamic focusing effect was adequately implemented, consistent with simulation predictions. The sensitivity of the system to detect labeled cells was improved by at least two-fold. By estimating the coverage of magnetic beads on cells, the signal from labeled cells could be predicted using a mathematical model, which also demonstrated the sensitivity of the signal to the height of the cells relative to the sensor. The system is versatile allowing interchangeable flow rates for cells with different diameters. [ABSTRACT FROM AUTHOR]