Amorphous Wires Research Articles

Torsion-Dependent Circular Magnetization in Fe-Based Amorphous Wire

The circular permeability,  =  + j, of a Fe73.5Cu1Nb3Si13.5B9 annealed (500oC, 1 h) amorphous wire was obtained from the measurements of impedance, Z = R + jX = R + jL, as a function of circular magnetic AC field (H = 0.15 – 200A/m) and applied torsion ( = -7.5 – 11.5 rad/m). So the influence of  upon the circular magnetization has been studied. We found that the effects of applied torsion on the circular magnetization can be explained by considering the magneto-elastic interaction and a helical domain structure in the sample. The large change of  with  may be used as a torsion sensor.

Nonlinear tensile deformation behavior of melt-extracted Co69.5Fe4.5Cr1Si8B17 amorphous wires

Metallic glasses often show excellent mechanical and physical properties due to their random atomic packing. But as a new kind of potential engineering material, metallic glasses have challenged the traditional processing methods. In this letter, continuous Co69.5Fe4.5Cr1Si8B17 metallic glassy wires at micrometer scales with a smooth surface and negligible fluctuation in diameter were prepared by the melt-extraction method. Their mechanical properties were evaluated by carrying out tensile tests. The Co69.5Fe4.5Cr1Si8B17 metallic glassy wires show high tensile fracture strength of the order of 2.8GPa and perform nonlinear deformation behavior prior to fracture. The tensile failure of the glassy wires was controlled by both the normal stress and shear stress.

Thermal Stability of Giant Magneto-impedance Effect in Glass-covered Amorphous Wires

Abstract Thermal stability of Giant magneto-impedance (GMI) effect of Co-based amorphous glass-covered wires was investigated. The temperature measurement was conducted in a special calorstat cell between 25 °C and 200 °C, and the GMI effect of the as-cast, glass-removed and DC annealed wires was measured at 100kHz-12 MHz ranging from 0 Oe to 80 Oe. Experimental results show that the ambient temperature has a significant influence on the thermal stability of GMI effect, it is caused by external conditions: driving frequency, magnetic field and sample states. The thermal stability and GMI fluctuating variation at different temperature of three-type wires could be quantificationally characterized by GMI max ratio variation difference Δ[ΔZ/Z max ] T max of three-type wires, and drastically improved with the driving frequency increasing to 10 MHz, and the working range of magnetic field for possible sensor applications should be below 10 Oe. While there is different from as-cast and glass-removed wires, DC annealed wire has twin-working-zone range (relatively low field 0 Oe-2 Oe & relatively high field 2Oe-10 Oe) of magnetic field at relatively high frequency (10 MHz) for sensor applications with different detection range of weak magnetic field. So, the improved thermal stability is caused by the co- actions of remarkable skin-effect, magnetic polarization and magneto-crystalline anisotropy energy with the increasing frequency. It therefore is concluded that the optimal driving frequency of 10 MHz and the detection range of weak magnetic field (2Oe-10 Oe) is favorable for the design parameters choices of high-performance GMI sensor.

Coil-Less Fluxgate Effect in Negatively Magnetostrictive Co<SUB>72</SUB>5Si<SUB>12</SUB><SUB>5</SUB> B<SUB>15</SUB> Amorphous Wire

Coil-Less Fluxgate Effect in Negatively Magnetostrictive Co<SUB>72</SUB>5Si<SUB>12</SUB><SUB>5</SUB> B<SUB>15</SUB> Amorphous Wire

High Performance Current Sensor Utilizing Pulse Magneto-Impedance in Co-Based Amorphous Wires

A pulse magneto-impedance noncontact sensor, was developed to detect small currents and subsequently the leakage current between two current carrying conductors. The sensing element is composed of Co-Fe-Mo-Si-B glass coated amorphous wire, placed between two μ-metal washers, which allows a simple differential arrangement, due to field symmetry and shielding against environment fields. High frequency excitation was realized by subjecting the wire to a sharp pulsed current provided by a micro-controller. The use of a micro-controller to drive the sensor allows an efficient and programmable way to establish optimal excitation parameters (pulse duration and periodicity) for high sensitivity of small magnetic field detection. There is also a potential of further improvements due to real-time digital filtering, data manipulation and the provision of a closed loop system. In an experiment simulating the leakage current, a resolution of less than 1 mA for a carrier current of few amperes was achieved, which is well below typical fault current levels of about 10 mA.

Orthogonal Fluxgate With Annealed Wire Core

Orthogonal fluxgate in fundamental mode has become a competitive sensor for low noise measurement of low frequency magnetic fields. The noise of this sensor has been recently reduced to 2.8 pT/√Hz at 1 Hz; however, it appears that noise lower than 2.5 pT/√Hz at 1 Hz cannot be achieved because of the physical limitations due to the intrinsic noise generated in the core of the fluxgate. In order to decrease the noise below 2.5 pT/√Hz at 1 Hz, Barkhausen noise generated in the core must be reduced. For this purpose, we annealed the amorphous wire used as the core of the sensor in an infrared furnace while a dc current was flowing through the wire. The dc current generated a circumferential field large enough to saturate the wire in a circumferential direction, and by annealing the saturated wire, we increased the circumferential anisotropy. We illustrate the dependence of circumferential anisotropy on dc current in the wire as well as on temperature and time of annealing. We then demonstrate that larger circumferential anisotropy helps reduce the noise of the sensor suppressing the Barkhausen noise when the fluxgate is operated in fundamental mode. As a result, a 1.8 pT/√Hz noise at 1 Hz was achieved with annealed wire, which is far below the 2.5 pT/√Hz minimum noise achievable for sensors with as-cast wires.

A high performance strain gage based on the stressimpedance effect in magnetic amorphous wires

The paper presents a study on the possibilities of using the Co based magnetic amorphous wires (MAWs) with nearly zero magnetostriction for measuring strains by exploiting the stressimpedance (SI) effect occurring on them. It is known that the SI is a particularization of the magnetoimpedance (MI) effect when a MAW is driven by an ac current and is subjected to mechanical stresses under constant magnetic field. Several parameters of influence have been investigated in order to obtain the best performances for a strain gage (SG) that is intended to be developed for finally building a high performance landslide transducer. Using a MAW of 20mm length which is driven by a current of 10mA and of frequency of 1MHz, under induced initial torsional stress of 5πrad/m and a residual axial tensile stress of 55MPa, we obtained a high sensitivity SG showing a gage constant of about 2100 and a linear range of ±200ppm.

Giant Magnetoimpedance Effect: Concept and Prediction in Amorphous Materials

Giant magneto impedance (GMI) effect was experimentally measured on as-cast, post-production and coated with chemical technique amorphous wire and ribbon materials consisted of varied chemical composition over a frequency range from 0.1 to 8 MHz under a static magnetic field between −8 and +8 kA/m. The results show that each amorphous sample has a certain operational frequency for which the GMI effect has maximum magnitude and the other parameters such as annealing and coating have a significant influence on the GMI effect. It is believed that the domain structure and wall mechanism in the material are responsible for this behaviour. A 3-node input layer, 1-node output layer artificial neural network (ANN) model with three hidden layers including 30 neurons and full connectivity between the nodes was developed. A total of 1600 input vectors obtained from varied treated samples was available in the training data set. After the network was trained, better results were obtained from the network formed by the hyperbolic tangent transfer function in the hidden layers, there was a sigmoid transfer function in the output layer and we predicted the GMI. Comparing the predicted values obtained from the ANN model with the experimental data indicates that a well-trained neural network model provides very accurate results.

Recent Advances of Pico-Tesla Resolution Magneto-Impedance Sensor Based on Amorphous Wire CMOS IC MI Sensor

We have developed sensitive micro magnetic sensors referred to as MI sensors based on magneto-impedance effect in amorphous wires and CMOS IC electronic circuits providing a sharp-pulse excitation. Micro sized MI-HIC chips have been in mass production of electronic compasses by Aichi Steel Corp. since 2002 for mobile phones and since 2010 for smart phones. Recently we have realized pico-Tesla (10-8 Oe) resolution for micro MI sensors making use of ultralow intrinsic magnetic noise in amorphous wires with the pulse magnetoimpedance effect. The pico-Tesla MI sensor is useful especially for bio-magnetic measurements without any magnetic shielding at room temperature. In order to avoid a risk of traffic accident due to noise reduction electric vehicles, an alert system for the pedestrians having a smart phone would be useful, if pico-Tesla MI sensor were built in the smart phones.

Magnetic Detector Based on GMI Effect of Amorphous Wire

The giant magneto-impedance (GMI) effect of amorphous wire and its affecting factors were analyzed. Magnetic impedance (MI) element was designed with a special structure. So the difficulties of complex negative feedback circuit and winding double circuits on amorphous wire were solved. High frequency current pulse generator, signal preprocessing circuit and digital signal processing module were designed. Thus a low magnetic field detector was realized. The sensor and the detector were tested in laboratory. The experiment results proved that the sensor had good linearity at the magnetic field range from -3 Oe to +3 Oe. The sensitivity reached 65 mv/Oe and the sensor had well temperature stability. The magnetic field resolution can reach 50 μOe and small magnetic target can be detected.

Physiological Magnetic Stimulation for Arousal of Elderly Car Driver Evaluated With Electro-Encephalogram and Spine Magnetic Field

Reliable evaluation for the arousal effect of magnetized olivine-crushed-stone-crammed vinyl pipe set on an elderly car driver's spine has been carried out measuring a four-points electroencephalogram using driving simulators considering a defined arousal index β/(δ+θ) . A sintered-magnetized-spherical-particles-crammed pipe is developed for realization of periodically pulse distributed surface magnetic field train matching with the magneto-protonics principle. Transition of the magnetic field time series generated from the spine with application of the physiological magnetic stimulation have also been measured using the amorphous wire and CMOS IC based pico-Tesla resolution magneto-impedance sensor, in which existence of alternative areas of cooperativeness and anti-cooperativeness for transition of the arousal index each other along the spine length direction is suggested. A special point on the central spine generating a large bio magnetic field of around 10 nT amplitude as well as corresponding pit of the stomach position was found.

Optimization of process parameters for developing FeCoSiB amorphous microwires through in-rotating-water quenching technique

The effects of process parameters for the in-rotating-water quenching technique have been investigated with respect to structural, magnetic and giant magneto-impedance (GMI) properties of FeCoSiB alloy microwires. Continuous and ductile amorphous wires have been found with the optimization of process parameters. The structural, magnetic and GMI behaviors have been evaluated as a function of wire diameter. The crystallinity of the wires increases with wire diameter, affecting soft magnetic and GMI properties. Consequently, it is found that the wire of 110 μm diameter shows superior soft magnetic and GMI properties.

Super MI Sensor: Recent Advances of Amorphous Wire and CMOS-IC Magneto-Impedance Sensor

We indicate that the Magneto-Impedance sensor using amorphous wires has reached a new stage to view "Super MI sensor technology" based on three main advantageous factors of (i) micro sized head and micro power consumption chip, (ii) ultra-high sensitivity micro magnetic sensor with 1 pico-Tesla resolution at the room temperature without any electromagnetic shielding, and (iii) ultra-quick response magnetic sensor with GHz operation. We summarize systematically the magneto-impedance technology with the basic principle and mechanisms of three advantageous features for constitution of various high performance new sensor devices such as the electronic compass chip for mobile phones and smart phones and portable sensors for the magneto-encephalography, the magneto-spinography, and various bio-cell magnetic measurements. Possibility of new application to MI antenna in magnetic telecommunications is also discussed.

Enhancing GMI properties of melt-extracted Co-based amorphous wires by twin-zone Joule annealing

The influence of twin-zone Joule annealing (TJA) on the microstructure and magnetic properties of melt-extracted Co68.2Fe4.3B15Si12.5 amorphous microwires has been investigated. Experimental results indicated that twin-zone Joule annealing treatment improved the GMI property of as-cast wires to a greater extent comparing with Joule annealing (JA) and conventional vacuum annealing (CVA) techniques. At 15MHz, e.g., the maximum GMI ratio [ΔZ/Z0]max of a TJA wire increases to 104.29%, which is more than 5 times of 20.49% for the as-cast wire, nearly two times of 56.47% for the JA wire, while the CVA wire has a decreased GMI ratio; the field response sensitivity of the TJA wire increased to 171.62%/Oe from 80.32%/Oe for the as-cast wire, exceeding the values of 140.76%/Oe for the JA wire and of 39.17%/Oe for the CVA wire. The stress or structural relaxation in TJA wire increases circumferential permeability, and magnetic moment achieves a critical state of excitation for overcoming eddy-current damping or “nail-sticked” action in rotational magnetization process at relatively high frequency. From the microstructural point of view, the role of regularly arranged atomic micro-regions (RAAM) and of medium range order region (MROR) determines the efficiency of various annealing techniques. Conclusively, TJA is established as an efficient annealing technique to enhance the GMI effect of wires, which can subsequently be used for detecting weak magnetic field at relatively wider working range (±2.0Oe).

Amplification of even Harmonics in Nonlinear Magnetoimpedance Response of Amorphous Wires in Presence of Longitudinal Alternating Magnetic Field

A model to describe the influence of longitudinal alternating magnetic field on the nonli-near magnetoimpedance in amorphous wires is proposed. The appearance of even harmonics in the voltage response is shown to arise from the asymmetry in the magnetization reversal process in the wire due to the presence of the longitudinal alternating field. The behavior of even harmonics is analyzed as a function of the external field, alternating field amplitude and current amplitude.

Noise Suppression Effect of Composites Containing Glass-Covered Amorphous CoFeSiBCr Wires

The noise suppression effect and its mechanism are investigated for a composite sheet and a composite film made of glass-covered amorphous CoFeSiBCr wires. Both samples show a significant noise suppression effect. The power loss ratio of the composite sheet is above 80% from 1.6 GHz to 8.5 GHz, and that of the composite film is above 70% from 3.2 GHz to 8.5 GHz even if its thickness is only 0.20 mm. The composite sheet demonstrates high real and imaginary permittivity above 30.7 and low real and imaginary permeability below 1.2. The surface resistivities of the two composite samples are as high as about 3×1012Ω/square. The power loss of the composite containing glass-covered wires should be mainly contributed by dielectric loss derived from electronic polarization and relaxation.

Study of Stress Annealing on Giant Magneto-Impedance in Glass-Covered Co-Based Amorphous Microwires

The glass-covered Co-rich amorphous wires was annealed by an applied stress during the current annealing process. The influence of stress and dc current annealing on the giant magneto-impedance (GMI) effect were investigated by the magneto-impedance. Our experiments showed that the magentic anisotropy is reduced by the annealing treatments, furthermore, the maximum GMI value is increased to 105 %.The GMI value is enhanced by increasing the outer domain volume and inducing a transverse anisotropy due to the changing of inner stress.

Magnetoelastic Effects and Distribution of Defects in Micrometric Amorphous Wires

The influence of defects and the magnetoelastic anisotropy term on the domain wall dynamics of glass-coated amorphous microwires is investigated. Using modified Sixtus-Tonks set-up, we have determined the position of the domain nucleation and measured the magnetic field dependence of the domain wall velocity. We found that both internal and applied stresses significantly affect the domain wall dynamics especially for wires with reduced magnetostriction. Particularly, we conclude that the non-linear relationship between the do- main wall velocity and magnetic field is correlated with the existence of defects which act as nucleation centers of additional domains.

Micromagnetic analysis of switching and domain structure in amorphous metallic nanowires

This paper describes a comprehensive micromagnetic model for the observed complex magnetic domains structures in amorphous wires with positive and negative magnetostriction with or without a glass cover. Many experimental studies and theoretical analysis have suggested several typical domain structures. We show the results of micromagnetic simulations that cover many of these observed data using a single set of physical hypotheses.

Ferromagnetic resonance in submicron amorphous wires

Ferromagnetic resonance in glass-coated amorphous wires with the diameter of metallic core varying from 25 μm to 133 nm is investigated. The microwave frequencies of 49.1 and 69.7 GHz are used and static magnetic field is applied either parallel or perpendicular to the long wire axis. In agreement with theoretical predictions the resonance curves of submicron wires substantially differ from the curves of the bulk wires. Depending on the symmetry and intensity of microwave electric and magnetic fields in the sample vicinity the circumferential and/or dipolar resonance modes can be excited. In bulk wires the resonance fields of the two modes coincide. In submicron wires, however, their resonance fields differ, indicating the metallic character of the circumferential mode and the insulator character of the dipolar mode. In wires with diameters 717 and 869 nm radial standing spin wave resonances are observed in parallel field configuration. The experimental results for the parallel field configuration can be well explained by the rigorous theoretical model. From the fit of experimental data the exchange stiffness constant A = 8.2 10−12 J/m and perpendicular surface anisotropy constant Ks = 6 × 10−4 J/m2 are obtained. The resonance curves measured in the transversal field configuration can be well explained in the frame of the skin effect and quasistatic approximations for the bulk and submicron wires, respectively. In submicron wires, however, an additional resonance of unknown origin is observed at higher magnetic fields.