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The main objective of the work is to investigate the capacity of a single magnetoresistance (MR) element to measure AC electrical currents. An instrumentation system is presented to characterize individually the four active elements of an MR bridge current sensor preserving their internal connections. The system suggests the possibility to sense electrical currents using only one element of the bridge opening the way to design new MR sensors based on this concept. Sensitivity, offset and non-linearity deviation were obtained using bridges of tunnel (TMR)- and giant (GMR)-based MR technologies. The single element embedded in a Wheatstone bridge configuration is used for practical current measurements in a 50 Hz line. An electronic circuitry is proposed to measure alternating (AC) currents with a single MR element, including a lock-in amplifier and an interface to properly convert the signal to its root mean square (rms) value with a resolution of 250 mA peak in the 125 A range. [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]

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]

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. [ABSTRACT FROM PUBLISHER]

This paper reports on the integration of magnetic tunnel junction (MTJ) sensing devices with magnetoresistance responses above 150% on flexible substrates. The sensors are integrated in a fabrication process based on polyimide materials, and demonstrate sensitivities up to 250~\mu \textV /Oe for bias currents in the 100- \mu \textA range. Assessment of the sensors performance is done under controlled mechanical load conditions, and the magnetoresistance is only slightly affected (1% variation) while sensitivity changes by 7.5% when the bending radii reduce down to 5 mm. The results demonstrate the high potential of the MTJ sensors to be used in applications requiring bending and conforming to non-planar geometries, bringing magnetoelectronic technologies to hard-to-reach regions of space. [ABSTRACT FROM PUBLISHER]

This paper describes how magnetoresistive materials can be optimized and integrated in magnetic field sensor devices. Giant magnetoresistive (GMR) and tunnel magnetoresistive (TMR) can provide advantageous solutions for a wide range of applications, of which some are described here. Considerations on field sensitivities, intrinsic noise mechanisms, biasing, and integration schemes are presented. [ABSTRACT FROM PUBLISHER]

Highly sensitive nanosensors with high spatial resolution provide the necessary features for high-accuracy imaging of isolated magnetic nanoparticles or mapping of magnetic fields. Here, we fabricated nanosensor devices based on MgO-magnetic tunnel junctions with soft pinned sensing layer. The exchange interaction at the free-layer is tuned to yield distinct linear operation ranges for the nanosensors. Circular (diameter D = 120–500 nm) and elliptical pillars with low aspect ratio (120 nm \times 130 nm–120 nm \times 200 nm) displaying a linear non-hysteretic transfer curves with tunnel magnetoresistance values up to 143% were obtained. A noticeable improvement in the sensitivity for circular structures from an average value of \sim 1 %/mT up to \sim 2 Hz with Hooge parameters within 1– 3 \times 10^{-9} \mu m ^{2}$ in the linear range. Nevertheless, such high sensitivity values are a major improvement in comparison with those reported previously for nanometric sensors, and extremely competitive with values reported for micrometric spin-valve sensors, with the advantage of providing a reduced device footprint suitable for highly resolved measurements. [ABSTRACT FROM AUTHOR]

In this work, arrays of MgO-based magnetic tunnel junction elements (5\times 20\ \mum^2) connected in series are studied for sensor applications. Linearization is obtained by combining shape anisotropy with a longitudinal hard bias field set by CoCrPt permanent magnets integrated on the sides of the array. We show that this architecture has the drawback of a large footprint in the chip, but is largely compensated by the weak bias voltage dependence and huge electric robustness, when comparing with individual magnetic tunnel junctions. [ABSTRACT FROM PUBLISHER]

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]

This paper presents a prototype of a platform for biomolecular recognition detection. The system is based on a magnetoresistive biochip that performs biorecognition assays by detecting magnetically tagged targets. All the electronic circuitry for addressing, driving and reading out signals from spin-valve or magnetic tunnel junctions sensors is implemented using off-the-shelf components. Taking advantage of digital signal processing techniques, the acquired signals are processed in real time and transmitted to a digital analyzer that enables the user to control and follow the experiment through a graphical user interface. The developed platform is portable and capable of operating autonomously for nearly eight hours. Experimental results show that the noise level of the described platform is one order of magnitude lower than the one presented by the previously used measurement set-up. Experimental results also show that this device is able to detect magnetic nanoparticles with a diameter of 250 nm at a concentration of about 40 fM. Finally, the biomolecular recognition detection capabilities of the platform are demonstrated by performing a hybridization assay using complementary and non-complementary probes and a magnetically tagged 20mer single stranded DNA target. [ABSTRACT FROM AUTHOR]

In this paper, we describe the development of multilayer (ML) thin films suitable for flux concentrators (FC). We prepared ML films having magnetic thicknesses n · tF in the range of 400 Å to 3000 Å by ion beam deposition (IBD). The films exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) long range antiferromagnetic (AF) coupling through very thin Ru interlayers. We prepared two types of samples: (CoFeB tF/Ru tRu)xn and (NiFe tF/Ru tRu)xn, where CoFeB is (Co70Fe30)80at%B20at% and NiFe is Ni81Fe19. The former has good thermal stability and high magnetic moment while the latter, previously reported, has poor thermal stability and low spontaneous magnetic moment. We discuss the magnetic properties of the films in terms of the remanent magnetic moment Mr and saturation field Hs. Despite having higher spontaneous magnetic moment of 1200 emu/cm3, (CoFeB/Ru)xn films with adequate magnetic proper. ties for sensor-in-gap devices with FC could not be prepared. By contrast, samples consisting of NiFe350 Å/(Ru7 Å/NiFe350 Å)x7 exhibited suitable magnetic properties. We lithographically patterned the films into FC and test structures to investigate their magnetization processes by anisotropic magnetoresistance (MR) measurements. The MR curves indicate magnetization processes by uniform rotation and show absence of hysteresis. [ABSTRACT FROM AUTHOR]

An analog isolator device, based on linear magnetic tunnel junctions is presented. Elemental single structures and full Wheatstone bridge devices are designed, fabricated and tested. In addition, the ranges of functionality of the devices are analyzed, mainly in terms of linearity, signal reconstruction and frequency response. [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 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.

One of the characteristic features of tunneling magnetoresistance (TMR) sensors is a strong influence of bias voltage on tunneling current. Since fundamental sensing characteristics of the sensors are primarily determined by the tunneling current, the bias voltage should impact these characteristics. Previous research has indeed showed the influence of the bias voltage on the magnetic field detection and sensitivity. However, the effect has not been investigated for nonlinearity and hysteresis and the influence of bias voltage polarity has not yet been addressed. Therefore, this paper systematically investigates the dependence of field sensitivity, nonlinearity, hysteresis and magnetic field detection of CoFeB/MgO/CoFeB-based magnetoresistance sensors on bias voltage magnitude and polarity. The sensitivity and field detection of all sensors improved significantly with the bias, whereas the nonlinearity and hysteresis deteriorated. The sensitivity increased considerably (up to 32 times) and linearly with bias up to 0.6 V. The field detection also decreased substantially (up 3.9 times) with bias and exhibited the minimum values for the same magnitude under both polarities. Significant and linear increases with bias were also observed for nonlinearity (up to 26 times) and hysteresis (up to 33 times). Moreover, not only the voltage magnitude but also the polarity had a significant effect on the sensing characteristics. This significant, linear and simultaneous effect of improvement and deterioration of the sensing characteristics with bias indicates that both bias voltage magnitude and polarity are key factors in the control and modification of these characteristics. [ABSTRACT FROM AUTHOR]

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]

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.

Abstract: An advanced model for quasi-linear spin-valve (SV) structures is presented for circuit simulation purposes. The model takes into account electrical and thermal effects in a coupled way in order to allow a coherent representation of the sensor physics for design purposes of electronics applications based on these sensor devices. The model was implemented in Verilog-A and used in a commercial circuit simulator. For testing the model, different SV structures have been specifically fabricated and measured. The characterization included DC measurements as well as steady-state and transient thermal analysis. From the experimental data, the parameters of the model have been extracted. The model reproduces correctly the experimental measurements obtained for devices with diverse sizes in different electrical and thermal operation regimes. [Copyright &y& Elsevier]