Asymmetric Magnetoimpedance Effect Research Articles

On the nature of the interlayer magnetic interactions in biphase ferromagnetic films

We report on the nature of the interlayer magnetic interactions in NiFe/Cu/Co films. By probing the quasi-static and dynamic magnetic properties of biphase ferromagnetic films, with soft and hard ferromagnetic phases intermediated by a non-magnetic layer, we address aspects of the coupling between magnetic layers. Our results demonstrate the nature of the interlayer magnetic coupling in biphase films. We also disclose the asymmetric magnetoimpedance effect as a fingerprint of the nature of the magnetic interlayer interactions playing key role in the magnetization dynamics of the system. We revisit in literature data and ideas on the asymmetric magnetoimpedance and the nature of the magnetic interactions in biphase ferromagnetic systems. Then, we compare our findings with results for biphase ribbons and microwires. Our observations raise the fundamental similarities and differences in the asymmetric magnetoimpedance of these structures.

Asymmetric Magnetoimpedance in Ferromagnetic Biphase Films: Effects of Magnetostatic Coupling and Number of Layers

A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered film is proposed. It is shown that a magnetostatic coupling changes the magnetization distribution in soft magnetic layers and leads to asymmetry in the field dependence of the impedance. The influence of the number of the repetitions of the base three-layered film structure having the soft and hard magnetic layers separated by non-ferromagnetic metallic spacer on the asymmetric magnetoimpedance is analyzed. The results of modelling describe main features of the asymmetric magnetoimpedance effect observed in bimagnetic multilayered films. The analysis shows that the multilayers may be attractive for use in miniature sensors of a weak magnetic field.

Invariance of the magnetic behavior and AMI in ferromagnetic biphase films with distinct non-magnetic metallic spacers

We investigate the quasi-static magnetic, magnetotransport, and dynamic magnetic properties in ferromagnetic biphase films with distinct non-magnetic metallic spacer layers. We observe that the nature of the non-magnetic metallic spacer material does not have significant influence on the overall biphase magnetic behavior, and, consequently, on the magnetotransport and dynamic magnetic responses. We focus on the magnetoimpedance effect and verify that the films present asymmetric magnetoimpedance effect. Moreover, we explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the probe current frequency in order to achieve higher sensitivity values. The invariance of the magnetic behavior and the asymmetric magnetoimpedance effect in ferromagnetic biphase films with distinct non-magnetic metallic spacers place them as promising candidates for probe element and open possibilities to the development of lower-cost high sensitivity linear magnetic field sensor devices.

Asymmetric magnetoimpedance effect in CoFeSiB amorphous ribbons by combination of field and current annealing for sensor applications

The roles of applied magnetic field during the current annealing of Co68.15Fe4.35Si12.5B15 soft magnetic amorphous ribbons are studied. Samples heat treated by Joule heating effect in open air and simultaneously in the present of longitudinal external magnetic field showed asymmetric magnetoimpedance (AMI) behavior. The AMI profile can be related to the exchange bias interaction between the soft magnetic amorphous material and a harder magnetic crystalline phase formed on the surface of the ribbon. This effect stems from thermal effect, the transverse Oe field generated from the annealing current which is thickness dependent and the longitudinal external field. The single peak AMI with the field sensitivity of 101%/Oe for DC annealing current is achieved. Our results could address a simple way to achieve the AMI response toward developing high sensitive magnetic field sensors.

Improving the sensitivity of asymmetric magnetoimpedance in exchange biased NiFe/IrMn multilayers

We investigate the asymmetric magnetoimpedance effect in exchange biased NiFe/IrMn multilayers and explore the possibility of tailoring the linear region of the curves around zero magnetic field by playing with the thickness of the ferromagnetic layers, probe current frequency, and the orientation between external magnetic field and exchange bias field direction. We quantify the sensitivity by calculating the |dZ/dH|H=0 in a wide range of frequencies. The highest sensitivity is observed for the thicker multilayer, reaching ∼160mΩ/Oe at ∼2.0GHz. The results place exchange biased magnetoimpedance multilayers as attractive candidates for the development of auto-biased linear magnetic field sensors.

Asymmetric magnetoimpedance effect in ferromagnetic multilayered biphase films

We investigate the magnetoimpedance effect in ferromagnetic multilayered biphase films. We verify that the films present asymmetric magnetoimpedance behavior and, by playing with the number of the repetitions of the base structure of the multilayer and the probe current frequency, we explore the possibility of tailoring the linear region around zero magnetic field in order to achieve higher sensitivity values. The highest sensitivity is observed for the thicker film, reaching ∼15mΩ/Oe at ∼0.52GHz. Thus, the results open the possibilities for application of ferromagnetic multilayered biphase films with asymmetric magnetoimpedance effect in sensors devices.

Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films

We investigate the magnetization dynamics through the magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance response is dependent on the thickness of the non-magnetic Cu spacer material. We verify asymmetric magnetoimpedance in films with biphase magnetic behavior and explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the thickness of the spacer and probe current frequency. We discuss the experimental results in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges, quasi-static magnetic properties, thickness of the spacer, and the kind of the magnetic interaction between the ferromagnetic layers. The results place films with biphase magnetic behavior exhibiting asymmetric magnetoimpedance effect as very attractive candidates for application as probe element in the development of auto-biased linear magnetic field sensors.

Asymmetrical magneto-impedance effect in NiFe/SiO2/Cu composite wire with a sputtered NiFe seed layer

In this work, a new type of asymmetrical magnetoimpedance (AMI) effect has been found in a new type of NiFe/SiO2/Cu composite wire without applying any dc-biased magnetic field, in which NiFe/SiO2/Cu composite wires were fabricated by sputtering a NiFe seed layer on the SiO2 layer and then electroplating another NiFe layer on the NiFe seed layer. A magnetization rotation model based on the coupling effect with bias field in the seed layer and the pinning effect by defects in the wire has been used to qualitatively explain the AMI profiles observed.

Asymmetrical Magnetoimpedance Effect in Partially Devitrified Co<SUB>66</SUB>Fe<SUB>4</SUB>Si<SUB>16</SUB>B<SUB>12</SUB>Mo<SUB>2</SUB> Ribbons

Asymmetrical Magnetoimpedance Effect in Partially Devitrified Co<SUB>66</SUB>Fe<SUB>4</SUB>Si<SUB>16</SUB>B<SUB>12</SUB>Mo<SUB>2</SUB> Ribbons

Design of a double core linear magnetometer based on asymmetric magnetoimpedance effect in nanostructured Finemet ribbons

Abstract The techniques used to produce magnetic sensors encompass many aspects of physics and electronics and are going to develop with each passing year. In this paper, we introduce a double core giant magnetoimpedance sensor. The sensing elements are provided by heat treating the FeCuNbSiB (Finemet) ribbons at 560 °C for 1 h to achieve a high magnetic permeability associated with the nanostructured state. Sensor cores are exposed to a dc current bias in order to provide asymmetric giant magnetoimpedance (AGMI) behavior. The sensor detects both direction and amplitude of the magnetic field with a sensibility of 2 mV/Oe.

Asymmetrical magneto-impedance effect in Fe-rich amorphous wires

Magnetoimpedance and magnetic properties of Fe-rich ferromagnetic amorphous wires of 0.050 mm diameter, prepared by an in-rotating-water technique following by a cold-drawing process to reduce the initial diameter of 0.125 mm, have been studied. A high value of magnetoimpedance phenomenon (about 60% real component and about 300% imaginary component) was measured in these microwires submitted to stress annealing by using the current annealing technique (annealing parameters: 150 mA during 90 min and 200 MPa). The application of a dc bias current affects strongly the field dependence of the magnetoimpedance ratio, inducing asymmetrical shape to the magnetoimpedance ratio. Such asymmetrical character is associated with the intrinsic helical anisotropy. The dc circular magnetic field produced by the dc electric current can modify in different ways the surface domain structure.

Asymmetrical magneto-impedance effect in torsion-annealed Co-rich amorphous wire for MI micro magnetic sensor

An asymmetrical magneto-impedance (MI) effect in almost zero magnetostrictive amorphous wires is obtained using torsion annealing and then magnetizing with a high frequency current biased with a DC current. A highly sensitive MI characteristic showing a field detection sensitivity of more than 100%/Oe was realized in the wire annealed with 450 turn/m torsion at 500/spl deg/C, inducing a spiral anisotropy. The change of the torsion direction from clockwise to anti-clockwise inverts the asymmetrical MI effect. A sensitive linear field sensor is successfully constructed using a pair of the asymmetrical MI heads without bias coils.

Asymmetrical Magneto-Impedance Effect in an Amorphous Wire with a Coil

A new method of obtaining the asymmetrical magneto-impedance (MI) effect in a zero-magnetostrictive FeCoSiB amorphous wire is presented, where in a wire coil is used to apply a wire pulse current. The mechanism for the generation of the asymmetrical MI effect is qualitatively explained by means of a magnetization rotation model for the surface layer of a wire with a spiral magnetization. A linear magnetic-field sensor circuit uses the amorphous-wire asymmetrical MI element magnetized with a sharp pulse train current in a C-MOS multivibrator circuit.

Asymmetrical magneto-impedance effect in twisted amorphous wires for sensitive magnetic sensors

An asymmetrical and sensitive magneto-impedance effect was realized in twisted FeCoSiB and CoSiB amorphous wires magnetized with a dc-biased ac current, in impedance up to about 120%/Oe. The asymmetrical magneto-impedance (AMI) is useful to construct linear field sensors without any dc bias field. Mechanisms of the AMI are also discussed.