Co-based Amorphous Ribbons Research Articles

PCB 다층 적층기술을 이용한 마이크로 플럭스게이트 자기 센서

To observe the effect of excitation coil pitch on the micro fluxgate magnetic sensor, two sensors are fabricated using multi layer board process and the pitch distance of excitation coil are and , respectively. The fluxgate sensor consists of five PCB stack layers including one layer of magnetic core and four layers of excitation and pick-up coils. The center layer as magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high DC permeability of and has a rectangular-ring shape to minimize the magnetic flux leakage. Four outer layers as excitation and pick-up coils have a planar solenoid structure and are made of copper foil. In case of the fluxgate sensor having the excitation coil pitch of , excellent linear response over the range of to is obtained with sensitivity of 780 V/T at excitation sine wave of and 360 kHz. The chip size of the fabricated sensing element is . The very low power consumption of is measured. This magnetic sensor is very useful for various applications such as: portable navigation systems, telematics, VR game and so on.

The GMI profiles of surface-removed amorphous ribbon

Results are reported on the giant magnetoimpedance (GMI) in soft-magnetic Co-based amorphous ribbons in view of their high potential for magnetic sensor applications. The thickness dependence of the GMI profile has been examined in surface-removed amorphous ribbons. The GMI valve characteristic decreases with increasing frequency, and asymmetric GMI profiles in the as-received state change into symmetrical ones with increasing etching time. The maximum of the GMI ratio, Δ Z/ Z, appears at a frequency of 1 MHz and decreases with increasing frequency. The frequency shift of Δ Z/ Z reveals the dominant process controlling MI effect in the amorphous region.

Near-surface magnetic properties of Co-based amorphous ribbons

The near-surface magnetic properties of as-cast and annealed (for various times in open air at a temperature T=380°C) Co 66Fe 4B 15Si 15 amorphous ribbons were studied by using a magneto-optical magnetometer. The effect of etching of the annealed samples on their near-surface magnetic properties was investigated. The annealed samples exhibit the presence of a hard near-surface magnetic layer. The hysteresis loops of the etched ribbons change strongly. For etching times ( t etch) larger than 50 s, an influence of the ribbon core on the near-surface magnetic properties of the sample was observed. For t etch>120 s, the hysteresis loops and other magnetic properties of the etched and as-cast samples were practically identical.

Co基アモルファスリボンの熱処理による磁気異方性と応力磁化特性

Stress-magnetization property changes in Co-based amorphous ribbons due to heat treatment were investigated. Co-based amorphous ribbons with a negative magnetostriction constant showed unique magnetization behavior under stress, such a stress-insensitive region and a peculiar magnetization increment. Our interpretation of the appearance of the unique stress-magnetization behavior is that three factors, i. e., an induced anisotropy field due to field annealing, a magnetoelastic anisotropy field under stress, and an exciting magnetic field along the sample axis, are responsible. A simple magnetization rotation process using the three factors shows a tendency for the stress-insensitive region to expand with larger induced magnetic anisotropy as same as the experimental results, however, it did not show any unusual magnetization increment. In interpreting the unique stress-magnetization characteristics, therefore, a transient magnetization process should be considered to be like a magnetic domain ramification and/or its reordering in conjunction with the above three factors.

Stress-magnetization change in amorphous ribbon due to magnetic field heat treatment

Stress-magnetization changes in Co-based amorphous ribbons annealed under magnetic field (magnetic field heat treatment) have been investigated. The stress-magnetization changes due to tensile stress were observed in positive increment of magnetization for the sample annealed under transversal magnetic field to its ribbon axis. However, a Co-based amorphous ribbon annealed under applied magnetic field parallel to the ribbon axis (longitudinal direction) did not show positive magnetization increment under applied tensile stress but showed stress insensitive region in magnetization change, which extended with increasing annealing temperature.

Near-surface magnetic properties and giant magnetoimpedance of Co-based amorphous ribbons

The study of near-surface local magnetic properties and giant magnetoimpedance (GMI) were carried out on Co 68Fe 4Cr 4Si 12B 12 amorphous ribbons. The amorphous ribbon was obtained by planar flow casting in air (samples N1). The second amorphous ribbon with the same composition (samples N2) was prepared from the part of the ribbon N1 by planar flow casting in a He atmosphere. Scanning Kerr microscopy showed that the studied samples have strongly distinguishing near-surface magnetic properties and different micromagnetic structure (equilibrium distribution of the magnetization). The magnetic field dependencies of GMI ratio profile in these ribbons were discovered to be also various.

High-temperature dependence of asymmetric giant magnetoimpedance and magnetostatic properties in Co-based amorphous ribbon

The asymmetric giant magnetoimpedance (GMI) and transversal Kerr effect (TKE) has been measured as a function of measuring temperature in the annealed Co-based amorphous ribbon. The hysteretic peculiarities on the temperature dependence of GMI and TKE on first thermal cycle are revealed in the temperature range 350–410 K. However, there is no significant hysteresis for second heating and cooling process. These results indicate that the first heating up to temperature nearly 350 K leads to irreversible modification of micro-structure of near surface layer.

Weak magnetic field annealing effect on magneto-optical and magnetostatic properties of Co-based amorphous ribbons

We have investigated modifications of magneto-optical properties in the weak-field annealed Co-based amorphous ribbons. It is found that spectral and magnetic field dependences of the transverse Kerr effect significantly change with the time of annealing in air and the magnetic field magnitude. The analysis reveals the existence of two anisotropies, one in low fields up to 300 Oe and another in the field over 2 kOe.

High-frequency magnetic aftereffect in Co-based amorphous wires and ribbons

In this work, the magnetoimpedance relaxation in Co 68.25Fe 4.5Si 12.25B 15 systems has been measured in the frequency interval 500 kHz–3 GHz. A comparison between ribbons, amorphous and glass-covered wires of nominal composition Co 68.25Fe 4.5Si 12.25B 15 was made. The time variation of the calculated characteristic impedance after field removal displays a similar behavior to the classic magnetic permeability aftereffect measured at lower frequencies by means of conventional fluxmetric techniques. Thermal treatments are shown to affect the impedance relaxations in melt-spun alloys. Conversely, no substantial effect has been observed in glass-covered wires.

Unique stress-magnetization change of Co-based amorphous ribbon due to magnetic field heat treatment

The stress-magnetization characteristics of Co-based amorphous ribbon were investigated. The sample annealed with longitudinal magnetic field to the ribbon axis showed unique stress-magnetization changes. These unique characteristics were observed only at a lower exciting magnetic field on the stress-magnetization measurement. They strongly depended upon the annealing temperature and ambient magnetic field intensity apart from exciting magnetic field for the measurements.

Temperature effect on the asymmetric giant magnetoimpedance in amorphous materials

The asymmetric giant magnetoimpedance (GMI) curve has been measured under the rotating field as a function of temperature in a Co-based amorphous ribbon (Co/sub 66/Fe/sub 4/B/sub 15/Si/sub 15/). The magnetic softness in the amorphous phase is enhanced at temperature between 370 and 415 K. The bias-field caused by the hard magnetic phase is nearly constant up to 350 K and then rapidly decreases with temperature. The field angle of 95/spl deg/ from the ribbon axis for maximum impedance increases to 97/spl deg/ at a temperature of 440 K, indicating little change of anisotropy configurations with temperature.

Depth profiles of magnetic anisotropy in annealed Co-based amorphous ribbon

For Co–Fe–Si–B amorphous ribbons the influence of weak-field annealing on transformation of magnetic field and spectral transverse Kerr effect (TKE) dependencies has been studied. The TKE spectra and magnetization curves were found to exhibit anisotropic behavior. The results indicate that the magnetic structure is inhomogeneous relative to thickness and confirm an increase of anisotropy in the near surface layer. It is suggested that the anisotropy is brought about by the shape effect of magnetic microcrystallites in the surface layer, the shape and size of which both change during annealing.

Magnetostatic and magneto-optical properties of Co-based amorphous ribbons

We have investigated the modification of the magneto-optical and magnetostatic properties on weak-field-annealed Co-based amorphous ribbon with thermomagnetic treatment. It is found that magneto-optical spectra and hysteresis loops change with annealing time and field in air. This analysis clarifies that the asymmetric giant magnetoimpedance is related to the appearance of the surface microcrystalline phase.

Asymmetric giant magnetoimpedance curve due to antiferromagnetic coupling

The asymmetric giant magnetoimpedance curves have been measured under the rotation of magnetic field on the weak-field annealed Co-based amorphous ribbons to analyze the characteristics of bias field. The bias field from the hard magnetic phases is expected to be of an order of 100 Oe along the annealing field direction. The effective field of soft magnetic phase in the field region parallel to the bias field is less than that antiparallel to the bias field, indicating that an antiferromagnetic exchange coupling exists between the magnetization of the soft phase and the bias field of the hard magnetic phases.

Ｃｏ基アモルファスリボンの熱処理による特異な応力磁化特性変化

The stress-magnetization properties of Co-based amorphous ribbons due to heat treatment were investigated. A sample was annealed with a longitudinal magnetic field applied to its ribbon axis. Examination of the stress-magnetization change revealed a stress-insensitive region that depended on the annealing temperature. To apply further stress, the magnetization of the sample was decreased to zero. However, examination of the magnetization change revealed a unique behavior due to a stress application at a lower exciting magnetic field (< 5 A/m). The stress-magnetization change showed irreversibility, with a maximum slightly larger than the initial magnetization value while the stress was decreased and then restored to the initial value. The results could be interpreted as implying a model of combined effects: a magnetic field parallel to the ribbon axis, an induced anisotropy field due to field annealing, and magnetoelastic anisotropy due to the applied tensile stress.

Determination of magnetization rotation and domain wall motion components in reversible complex susceptibility spectra of Co-based amorphous ribbons with various annealing times

The complex susceptibility spectra for the Co 66Fe 4Ni 1B 14Si 15 ribbons annealed at 380°C under external magnetic field of 3 Oe with various annealing times were measured in reversible magnetization range. The susceptibility spectra originating from both relaxation processes of reversible domain wall motion and magnetization rotation are separated from the complex susceptibility spectra measured for the samples. The variation of static susceptibilities and relaxation frequencies of domain wall motion and magnetization rotation with annealing time indicate that the alignment of domains to external field direction onset at the annealing time is about 5 min and is accomplished at about 20 min. For short annealing time <5 min, magnetic softening is the main effect on magnetization processes.

Role of surface crystalline phases in magnetoimpedance in Co-based amorphous ribbons

The giant magnetoimpedance (GMI) profile at 0.1 MHz shows one-peak behavior in vacuum-annealed samples at T=380°C, irrespective of annealing time t a from 20 to 480 min. For the samples annealed in open air, the GMI profile shows two peaks for t a=20 min annealed sample. However, one of the peaks disappears and the asymmetric GMI profile exhibits a drastic step-like change near zero field for t a⩾300 min. Such an asymmetric GMI characteristic is probably due to the magnetic coupling of amorphous phase with a relatively hard magnetic phase on surface microstructures of FCC-Co, HCP-Co and Co 2Si crystalline phases.

Magneto-impedance in Co-based amorphous wire and ribbon

Magneto-impedance of Co-based amorphous alloys with low magnetostriction ( λ) and in the form of wire and ribbon is measured as a function of longitudinal d.c. magnetic field ( H) for frequencies up to 100 KHz. Nearly 100% drop in reactance is found in wire and ribbon with small and negative λ for H≈30 Oe. The field sensitivity of impedance goes down for alloys with higher values of λ. The longitudinal external stress reduces the reactance.

Temperature dependence of asymmetric GMI profile

The giant magnetoimpedance (GMI) profiles have been measured as a function of measuring temperature from 300 down to 50 K for the Co-based amorphous ribbons annealed in vacuum (A-sample) and in open air (B-sample) under the annealing field of 3 Oe. The contribution of wall motion on GMI decreases more sensitively with the decreasing temperature than that of rotational magnetization in both samples. The asymmetry and hysteresis of the profiles for increasing and decreasing fields also decrease with the decreasing temperature.

Frequency characteristics of permeability in weak-field annealed Co-based amorphous ribbon

The Co-based amorphous ribbons were annealed under the weak-field of a few hundred A/m at a temperature of 380°C for 8 h in an air atmosphere. The annealing field H a was applied along the sample axis during the annealing to develop the bias field in crystalline layer on the sample surface. Two relaxation due to wall motion and rotational magnetization are revealed in low and high frequency region, respectively, for as-quenched and annealed samples in vacuum under zero field. For the annealed samples in air, the low frequency relaxation due to domain wall motion drastically decreases, while the high frequency relaxation due to rotational magnetization remains irrespective of H a These results indicate that the wall of longitudinal domains are strongly coupled with the bias field, while the rotational magnetization is enhanced in the annealed samples under the field.