Papers by Keyword: Giant Magnetoimpedance

Abstract: The structure, magnetic properties, ferromagnetic resonance and giant magnetoimpedance effect (GMI) were studied in Fe_xNi_100-x thin films and multilayered systems having compositions with small deviation from zero magnetostriction in order to find the best conditions for possible applications in the area of small pressure sensors. A comparative analysis of the effective magnetization and g-factor was carried out for the thin films of Fe_xNi_100-x (x = 19.8, 17.5, 15.0, 11.9) alloys. Comparison of the concentration dependences for static 4πM_s and dynamic 4πM_eff magnetization values allows to select a narrow interval of concentrations around Fe₁₅Ni₈₅ for the development of a microfluidic small pressure sensitive elements based on GMI effect. The maximum value of GMI ratio (ΔZ/Z) ratio shows linear dependence on the iron content in the Fe_xNi_100-x alloy for the concentration range under consideration.

Abstract: Operation on the principle of the giant magnetoimpedace (GMI) magnetic field sensor was designed and tested for the case of CoFeSiB amorphous wire of 6 mm length. We considered magnetic field displacement of the order of 10 Oe. Piece of amorphous wire was placed as a central conductor of a coaxial cable. The maximum slope of the sensor GMI characteristic was observed at the terminator resistance R_T = 50 Ohm, while the maximum of the GMI ratio variation was observed in the not “matched” (R_T = 75 Ohm) but closer to the “short” mode. Amorphous wire placed as a central conductor of a coaxial cable serves as a sensitive element with high sensitivity with respect to applied field making possible to use a simple design with a miniature coil for magnetic field biasing.

Abstract: This work presents a systematic study of the effects of current pulsation on soft magnetic properties and giant magnetoimpedance (GMI) of nickel-iron (NiFe) coatings electrodeposited on copper wires. The specimens were prepared by the electrodeposition technique with controlled bath compositions and varied applied current waveforms. The microstructural and chemical investigations indicate that current pulsation with 50% duty cycle and 50 Hz frequency provides significantly smoother coating surface of uniform nodules, with comparable Fe content but different phase composition, as compared to the direct current condition. The vibrating sample magnetometer evidently shows that the deposits prepared with a pulsed current exhibit relatively small coercivity, below 4 Oe. Using the four-point probe technique, the MI ratio of the pulse deposits is found to reach a significantly high value above 2,000% with decent sensitivity. The benefits of current pulsation in improving the characteristics of NiFe deposits, and correspondingly the alloys’ soft magnetic properties and MI effects are demonstrated.

Abstract: The influence of DC current annealing on magnetic properties and the frequency dependence in the range from 0.1 to 20 MHz of the giant magnetoimpedance effect (GMI) of glass-covered amorphous microwires were investigated. Under a certain annealing condition (10 min annealing with applied current Ia=110 mA), the maximum change of impedance was about 200% with a maximum slope sensitivity of 0.26%/Am-1 . Further treatment with increased current resulted in a decrease of the maximum MI ratio. Meanwhile, annealing can produce short-range order relaxation and consequently improves the sample's soft magnetic properties. We also found that the GMI ratio increased due to the enhanced induced anisotropy with increasing current under the same Joule energy.

Abstract: A highly sensitive magnetic sensor using the GMI (Giant Magneto Impedance) effect has been developed. The sensor performance is studied and estimated. The sensor circuitry consists of a Square wave generator (driving source), a sensing element in a form of composite wire of a 20μm copper core electrodeposited with a thin layer of soft magnetic material (Ni₈₀Fe₂₀), two amplifier stages for improving the gain from the sensor element, switching mechanism, scaler circuit, an ac power source driving the permeability of the magnetic coating layer of the sensing element into a dynamic state, and a signal pickup LC circuit formed by a pickup coil and an capacitor .The results showed that for high sensitivity and resolution (10^-7 T), the frequency and magnitude of the ac driving current through the sensing element each has an optimum value, the resonance frequency of the signal pickup LC circuit should be equal to or twice as the driving frequency on the sensing element, and the anisotropy of the magnetic coating layer of the sensing wire element should be longitudinal.

Abstract: A novel excellent response of giant magnetoimpedance effect was found out in a magnetic LC-resonator consisting of a glass-coated amorphous Co83.2B3.3Si5.9Mn7.6 microwire and two capacitive cylindrical electrodes at the end of the microwire. The shapes of the impedance curves plotted vs. applied external dc-field varied dramatically with increasing frequency. The phase angle was also strongly found to be dependent on this field. The impedance curves were changing abruptly at near the resonance frequency. Because the permeability of ultra soft magnetic microwire is changing rapidly as a function of external magnetic field, the resonance frequency as well as impedance of the LC-resonator also changes drastically with respect to the external magnetic field. The maximum magnetoimpedance ratio value was reached as much as 1,600%. The sudden changes of phase angle as much as 180 degree evidenced the occurrence of resonance phenomenon. These results are promising for developing ultra-high sensitive magnetic sensor applications.

Abstract: Fe86.5Zr7B3Cu3.5 nanocrystalline ribbon can be directly fabricated by melt – spinning technique with an appropriate quenching speed without annealing processes. The average grain size of α-Fe for Fe86.5Zr7B3Cu3.5 as quenched ribbon prepared with a quenched speed V=40 m/s is about 10-13 nm estimated from X-ray diffraction and TEM observation. For Fe86.5Zr7B3Cu3.5 nanocrystalline as quenched ribbon (V=40m/s), the saturation magnetic induction Bs is 1.47 T, permeability μe at 1 kHz is 25600 and saturation magnetostriction λs is -2×10-6. The magnetoimpedance value Z/Z0 of the Fe86.5Zr7B3Cu3.5 nanocrystalline as quenched ribbon reaches –38.32 % under H=7162 A/m. Our present results reveal a novel route to fabricate the nanocrystaline ribbons with excellent soft magnetic properties and giant magnetoimpedance.