Magnetoimpedance Change Research Articles

Analog of giant magnetoimpedance in magnetized ε-near-zero plasma.

In this Letter, we show that magnetized plasma with properly designed parameters at plasma frequency suffers a large magnetoimpedance change under a moderate external magnetic field. Such an interesting feature can be described as the analog of giant magnetoimpedance (GMI), which is confirmed by detailed calculation. GMI devices based on magnetized ε-near-zero plasma do not require microfabrication, and they are capable of working at tunable frequency, even in terahertz frequency range; more importantly, they can be dynamically controlled by environmental parameters such as temperature and pressure.

Magnetic Domain of Stepped Magneto-Impedance Sensor Controlled by a Normal Magnetic Field

A thin-film magneto-impedance (MI) sensor has the unique property of a step-like magneto-impedance change, in the case where the sensor has an in-plane uniaxial inclined easy axis. A domain observation shows that the step-like change is due to a magnetization transition within three states, including the longitudinal single domain with parallel state, that with anti-parallel state and the inclined Landau-Lifshitz domain (ILLD). In a condition where the sensor has an easy axis of 70º relative to the short-side axis of the rectangular element, the transition is limited between the parallel and anti-parallel states despite the existence of a stable ILLD. Previous work showed that the application of a normal field could produce the ILLD state. This paper reports a control method for the magnetic domain by controlling the normal field. It is shown that the existence of a distributed canted angle relative to the normal direction in the normal field enhances the reconstruction of the ILLD domain state.

Magnetoimpedance Effects in Electrodeposited NiFe Nanowire Array

In this work, NiFe nanowires were grown in highly ordered porous anodic alumina oxide templates by dc electrodeposition at a pH value of 2.6. Scanning electron microscopy showed that wires have diameters of about 250 310 nm and length 25 30 μm. The energy dispersive X-ray analysis showed that the composition of the nanowires is Ni65Fe35. Electrical contacts were made on both sides of the nanowire array and their magnetoimpedance properties were investigated. All the magnetoimpedance curves showed single peak behavior due to the high shape anisotropy. The maximum magnetoimpedance change at the 79 MHz driving current frequency was ≈ 1.45%.

Ultrasensitive detection of Dynabeads protein A using the giant magnetoimpedance effect

We report on a biosensing system for ultrasensitive detection of Dynabeads protein A (DPA) that employs the magnetoimpedance (GMI) effect. The system is capable of detecting DPA via magnetic signals in the form of a magnetoimpedance change. The GMI ratio shows distinctive changes because of the induced fringe field produced by the superparamagnetic Dynabeads. The GMI ratio undergoes an overall downturn at high frequencies, but the drop becomes smaller with increasing DPA concentration. This phenomenon has not been observed so far. At a concentration of 0.1 μg mL−1, the GMI ratio drops by 8.53 % at a frequency of 1.4 MHz. In other word: almost 90 Dynabeads can be detected. We believe that this novel scheme has a large potential in high-sensitivity and miniaturized immunoassays.

Development of an ingenious method for determination of Dynabeads protein A based on a giant magnetoimpedance sensor

A novel analytical method based on giant magnetoimpedance (GMI) effect is developed for quantitative determination of Dynabeads protein A (DPA). An integrated GMI sensor involving the sensing elements of NiFe/Cu/NiFe films is prepared by Micro-Electro-Mechanical-Systems (MEMS) technology. DPA with various concentrations are immobilized on Au film, and a GMI-based biosensing platform is established. The magnetic signals produced by DPA are sensed by the GMI sensing elements, and the GMI sensor provides a detection signal in the form of a magnetoimpedance change. We observed that the GMI ratio is greatly reduced at high frequencies due to the presence of DPA. The GMI sensor displays a linear range of 0.1–5μgmL−1, and a low detection limit (90 Dynabeads) is achieved at f=1.5MHz. Therefore, this GMI-based analytical method may be useful for highly sensitive detection of biological markers in ultra-trace quantities.

Room temperature giant magnetoimpedance in La 0.7Ba 0.15Sr 0.15MnO 3 compound

Polycrystalline La 0.7Ba 0.15Sr 0.15MnO 3 compound shows giant magnetoimpedance (GMI) effect at low field and at low frequency under a temperature range from 300 K to its Curie temperature ( T C). A sharp change in magnetoimpedance is obtained at low fields up to 1 kG, followed by a nearly linear increase at higher field. The frequency dependence of magnetoimpedance becomes prominent near T C only, where as near room temperature; magnetoimpedance shows feeble frequency dependence in MHz region. Present investigation reveals that magnetoimpedance in La 0.7Ba 0.15Sr 0.15MnO 3 compound could be exploited as a sensitive tool for room-temperature magnetic field sensing.

Influences of Extra Magnets on Giant Magnetoimpedance Effect in Amorphous Wires

Adjacent extra magnets can induce an additional impedance to an amorphous wire. We have studied the additional impedance passing through a magnetic ring and found that it is related to the electromagnetic characteristics, shapes, and locations of the extra magnet and the frequency of the ac excitation, regardless of the amorphous material properties and the extra magnetic field conditions. According to our theoretical analysis, the additional impedance severely reduces the magnetoimpedance change of the amorphous wire and destroys the giant magnetoimpedance characteristic. We therefore propose a return structure to diminish the additional impedance. Our experiments measured the impedances of an amorphous wire, a Cu wire, and the return structure with a variety of extra magnetic fields. The results confirmed the characteristics of the additional impedance and verified the effectiveness of the return structure.

Analysis of magnetoimpedance in amorphous wire passing through a magnetic ring

A unified expression of magnetic susceptibility tensor is presented according to the magnetic-moment motion equation with Landau-Lifshitz damping term and Gilbert damping term. The application of equivalent magnetic permeability enables to transform the anisotropy problem to an isotropy one with the same electromagnetic solution in amorphous wire. By this transformation, the impedance of amorphous wire passing through an insulating or conducting magnetic ring are analyzed. Additionally, the magnetoimpedance effect in amorphous wire through a magnetic ring is simulated by the numerical analysis based on the finite element method. The results of theoretical analysis and numerical simulation, which agree with each other, indicate that the additional impedance caused by extra magnetic objects seriously reduces the magnetoimpedance change of amorphous wire and destroy the giant magnetoimpedance characteristic. Therefore, the return wire structure is proposed to diminish the additional impedance. The simulation results verified the effectiveness of this method.

Giant magnetoimpedance: A label-free option for surface effect monitoring

The change in magnetoimpedance (MI) during surface modification of the magnetic sensitive element caused by highly corrosive fluid was studied with the aim of creating a robust method to monitor the surface effects. A MI-based sensor prototype with an as-quenched FeCoSiB or FeCoCrSiB amorphous ribbon sensitive element was designed and calibrated for a frequency range of 0.5–10MHz at an intensity of the current of 10–60mA without bath for fluids. Measurements as a function of the exposure time were also made in a regime where chemical surface modification and sensing were not separated (in a bath for fluids). The MI variation was explained by the change of the surface magnetic anisotropy and the geometry of the sensitive element. A simple model was developed to describe MI change. It was shown that the magnetoimpedance effect can be employed as useful method to probe the electric features of surface-modified magnetic electrodes when the corrosive fluid, the material of the sensitive element, and the detection conditions are properly selected.

Giant magnetoimpedance effect in Fe–Nb–B ribbon

In the present paper we report first evidence of a giant magnetoimpedance effect in Fe–Nb–B ribbon after heat-treatment . The magnetoimpedance change (Z(H=65 Oe)−Z(0))/Z(0) for the longitudinal case can reach the value of −41.78%. The absolute value of ( Z( H)− Z(0))/ Z(0) is smaller for the transverse case than for the longitudinal case, due mainly to the demagnetization effect.