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A phenomenological model to describe the transverse differential susceptibility in the field-annealed CoFeBSiamorphous ribbon is developed. The exchange bias between surface crystalline layer and amorphous bulk is described by means of an exchange bias field. The model allows one to calculate the external field dependence of the transverse differen...
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The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons is studied. It is assumed that the ribbon consists of an amorphous bulk and two surface hard magnetic crystalline layers appearing after the annealing. The off-diagonal magnetoimpedance is calculated in the framework of the quasi-static...
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Citations
... According to the literature [1,6,7,[14][15][16][17][18][19][20][21][22], the AGMI effect can be induced by three main factors: (a) dc currents, (b) high frequency alternating magnetic fields and (c) exchange bias, which employs annealing techniques to enforce an intrinsic asymmetric behavior. In this paper, the AGMI effect was induced by dc currents, which, if properly chosen, can be used to increase the sample sensitivities. ...
The giant magnetoimpedance effect (GMI) is used in the most recent technologies developed for the detection of magnetic fields, showing potential to be applied in the measurement of ultra-weak fields. GMI samples exhibit a huge dependency of their electrical impedance on the magnetic field, which makes them excellent magnetic sensors. In spite of GMI magnetometers being mostly based on magnitude impedance characteristics, it was previously verified that sensitivity could be significantly increased by reading the impedance phase. Pursuing this idea, a phase-based GMI magnetometer has been already developed as well as an electronic configuration capable of improving the phase sensitivity of GMI samples. However, when using this topology, it was noted that the sensitivity improvement comes at the cost of reduced voltage levels in the reading terminal, degrading the signal-to-noise ratio. Another drawback of the electronic configuration was that it was not capable of enforcing a linear behavior of the impedance phase in the function of the magnetic field in a given operation region. Aiming at overcoming those issues and then optimizing the behavior of the circuit developed to improve the phase sensitivity, this paper mathematically describes a completely new methodology, presents an enhanced newly developed electronic topology and exemplifies its application.
... GMI sensors developed by AMI Co. are producing bias magnetic field on the amorphous wire head by applying dc or ac pulse current on the bias coil wound on the head to obtain asymmetric GMI effect [3] . Recently , a very large asymmetric GMI effect has been observed and studied in field-annealed [5]–[8] and stress/field-annealed [9], [10] Co-based amorphous ribbons in air. The asymmetric GMI effect in the field-annealed amorphous ribbon has self-biased advantage in constructing linear GMI sensor because there is no need for external biasing and bias coil to make the asymmetric GMI. ...
Recently sensitive micro-magnetic sensors are strongly required in various technologies such as BT and IT. This paper gives the comprehensive analysis of the Asymmetric Giant MagnetoImpedance (AGMI) sensor's performance with negative feedback. Asymmetrical behavior of the GMI is required for linear magnetic field sensors as the sensitivity and linearity for magnetic field are the most important parameters in the practical application of GMI to magnetic sensors, and this has been realized by magnetic field annealing in amorphous ribbon. A novel AGMI sensor was developed and the performance of the sensor was carefully studied with and without applying negative feedback. The sensor uses 10 mm times 1 mm times 20 mum Co<sub>66</sub>Fe<sub>4</sub>Si<sub>15</sub>B<sub>15</sub> ribbon as a sensing element. On applying the negative feedback the sensor shows excellent linearity free from hysteresis, independent of temperature variations. The sensitivity AGMI sensor was found to be 0.27 V/Oe in dynamic range of -2 ~ 2 Oe.
Magnetic bias phenomena of field-annealed CoFeSiB amorphous ribbons showing asymmetric giant magnetoimpedance was investigated by MOKE method. The specimens removed the crystalline layer at one surface side by chemical etching were prepared and measured magnetization curves by MOKE to investigate the effect of the crystalline layer on magnetization of inner soft amorphous phase. We observed the shift of hysteresis loop, and concluded that the crystalline layer exerts bias field effect on inner soft amorphous phase and the direction of bias filed is opposite to the magnetization direction of surface crystalline layer.
The off-diagonal magneto-impedance in Co-based amorphous ribbons was measured using a pick-up coil wound around the sample. The ribbons were annealed in air or in vacuum in the presence of a weak magnetic field. The evolution of the first and second harmonics in the pick-up coil voltage as a function of the current amplitude was studied. At low current amplitudes, the first harmonic dominates in the frequency spectrum of the voltage, and at sufficiently high current amplitudes, the amplitude of the second harmonic becomes higher than that of the first harmonic. For air-annealed ribbons, the asymmetric two-peak behaviour of the field dependences of the harmonic amplitudes was observed, which is related to the coupling between the amorphous phase and surface crystalline layers appearing after annealing. For vacuum-annealed samples, the first harmonic has a maximum at zero external field, and the field dependence of the second harmonic exhibits symmetric two-peak behaviour. The experimental results are interpreted in terms of a quasi-static rotational model. It is shown that the appearance of the second harmonic in the pick-up coil voltage is related to the anti-symmetrical distribution of the transverse field induced by the current. The calculated dependences are in qualitative agreement with the experimental data.
Magnetoimpedance (MI) and hysteresis loops were studied in electroplated Ni79.1Fe20.9/Cu, Ni75.64Fe24.26Ru0.10/Cu, Ni79.51Fe20.31Ru0.18/Cu and Ni75.99Fe23.66Ru0.34/Cu wires. Scanning electron micrographs showed that crack-free electroplated wires were obtained with a smooth surface. The average grain size varied between 3 and 10 µm for all samples. It was found that circumferential anisotropy was induced in all samples during the electroplating process. The maximum MI response was 459% at a frequency of 90 kHz, 361% at 110 kHz, 157% at 100 kHz and 114% at 340 kHz for Ni79.1Fe20.9/Cu, Ni75.64Fe24.26Ru0.10/Cu, Ni79.51Fe20.31Ru0.18/Cu and Ni75.99Fe23.66Ru0.34/Cu wires, respectively.
