Heebok Lee

Temperature dependence of magnetoimpedance effect in amorphous Co66Fe4NiB14Si15 ribbon

The temperature dependence of the magnetoimpedance (MI) effect is important both for scientific study and for thermal stability of MI sensors. We have performed the measurement of MI effect in amorphous Co66 Fe4 NiB14 Si15 (Metglas 2714A) ribbon from a cryogenic chamber where the temperature of the sample can vary from 10 to 300 K. The ac current was fixed at 10 mA for all measured frequencies ranging from 100 kHz to 10 MHz. The magnetoimpedance ratio (MIR) was revealed the drastic increment as a function of MIR(T)=MIR(0)exp(cT2), where c is a constant. The measured MIR values at room temperature are usually 2–3 times larger than the data measured at 10 K for all measured frequencies. However, the shapes of the MIR curves are remained. This result shows the potential application of the MI effect for a temperature sensor.

Magnetoimpedance effect in the nanocrystalline Fe–Zr–Cu–B–Al alloy system

The magnetoimpedance (MI) of Fe92−x−yZr7BxCu1Aly (x=2,4,6,8,y=0,0.5,1,1.5) alloys has been measured to investigate the influence of the structural changes in the crystallization process as well as the changes of the soft magnetic properties such as permeability, magnetic anisotropy, etc. after thermal treatment. The MI measurements were carried out along the ribbon axis with longitudinal magnetic field. The nanocrystalline alloy system was prepared by the rapid quenching technique in an Ar atmosphere. Ultrasoft magnetic behavior has been observed in all samples annealed at 550 °C. The x-ray diffraction and transmission electron microscopy results show the α-Fe phase appeared in the annealed alloy system at 550 °C. The maximum magnetoimpedance ratio value in Fe84Zr7B3Cu1 alloy annealed at 550 °C was reached as much as 1100%. The field annealing does not contribute to improve the magnetoimpedance effect in these nanocrystalline alloy system.

MAGNETOIMPEDANCE EFFECT IN NANOCRYSTALLINE FE90-XBXZR7CU1AL2 (X=2,4,6,8) ALLOYS

The magnetoimpedance of Fe90−xBxZr7Cu1Al2 (x=2,4,6,8) alloys has been measured to investigate the influence of the structural changes in the crystallization process as well as the changes of magnetic properties such as permeability, coercivity, magnetic anisotropy, etc. after thermal treatment. The frequency of magnetoimpedance measurement ranged from 100 kHz to 10 MHz, and the current was fixed at 10 mA for all measurements. Annealing was performed at temperatures of 350, 450, and 550 °C for 1 h in a vacuum. Ultrasoft magnetic behavior has been observed in the samples annealed at 450 °C. The magnetoimpedance ratio coincides with the softness of magnetic properties of thermally treated samples. A giant change of the longitudinal permeability as a function of external field is also observed.

Giant Magnetoimpedance Effect in Co70Fe5Si15B10 and Co70Fe5Si15Nb2.2Cu0.8B7 Ribbons

Giant magnetoimpedance (GMI) effect has been observed in Co70Fe5Si15B10 and Co70Fe5Si15Nb2.2Cu0.8B7 melt-spun amorphous ribbons. The magnetoimpedance (MI) of these samples has been studied up to a frequency of 10 MHz and varying a dc magnetic field (Hdc) within 150 Oe. A maximum change of 89% in MI has been observed for Co70Fe5Si15Nb2.2Cu0.8B7 composition around a frequency of 3.1 MHz. Substitution of Cu and Nb for B in an initial Co70Fe5Si15B10 composition forming the Co70Fe5Si15Nb2.2Cu0.8B7 composition not only favors the GMI effect but also gives rise to the sensitivity of the magnetic response (~18%/Oe), which is very beneficial for magnetic sensors applications. The GMI effect for both samples annealed at 550 K is further enhanced due to the presence of the ultrasoft magnetic materials, compared to their as-quenched samples.

Incremental permeability and magnetoimpedance effect in mumetal film annealed by using rapid temperature annealing technique

Abstract The angular dependence of the incremental permeability and the magnetoimpedance (MI) effect has been investigated in conjunction with the induced magnetic anisotropy in Ni 77 Fe 14 Mo 5 Cu 4 wt.% film by thermal treatment in an external magnetic field. The mumetal film was prepared by the rf magnetron sputtering method in Ar atmosphere. The maximum magnetoimpedance ratio (MIR) of the as-deposited sample and the thermally treated sample were 75% and 70%, and the MI sensitivities measured at 36.5 MHz were 29%/Oe and 40%/Oe, respectively. The depth of the double peak in the MIR curve and the transverse incremental permeability ratios (TPR) are directly related to the magnetic anisotropy. The MI sensitivity in the depth of the MI curve in the film improved by the thermal treatment is large enough for magnetic sensor application.

Influences of annealing and wire geometry on the giant magnetoimpedance effect in a glass-coated microwire LC-resonator

The influence of annealing and of wire geometry on the giant magnetoimpedance (GMI) effect in a glass-coated microwire LC-resonator were systematically investigated. It was found that annealing magnetic microwires significantly varied the permeability and hence the GMI ratio, whereas the magnetoimpedance response was sensitively altered with varying wire geometry of the LC-resonator. The magnitude of GMI is determined by the soft magnetic characteristics of the microwire and the effect of LC-resonance, while the multiple-peak GMI feature can be attributed to the LC-resonance circuit and the formation of standing magnetic waves within the sample. Interestingly, the GMI ratio reached the largest values of 400 000% and 270 000% at the resonance frequencies of 518.51 MHz and 146.32 MHz for Co83.2B3.3Si5.9Mn7.6 and Co67Fe3.8Ni1.4B11.5Si14.6Mo1.7 samples, respectively. The corresponding magnetic-field sensitivities of GMI are about 218 000%/Oe and 135 000%/Oe. These results are interesting for the development of a new family of ultra-sensitive and high-frequency magnetic sensors. The feature of a LC-resonance circuit can be used for improving the sensitivity of GMI-based magnetic sensors while selecting the working frequency.

Ultra-soft magnetic properties in nanocrystalline Fe81B11Nb7Cu1 alloy

The extremely soft magnetic behaviors in the nanocrystalline Fe_(81)B₁₁Nb_7Cu₁ alloy annealed at 450 ℃ and 550 ℃ for 1 hour in a vacuum were investigated by means of the magnetoimpedance (MI) effect and the incremental permeability. Because the MI effect can be obtained only in ultra-soft magnetic materials, the improvement of magnetic softness by proper thermal treatment was carefully monitored by the MI effect for all annealed samples. The changes of the incremental permeability as a function of an external field were also measured to verify the magnetic softness along with the MI measurement.

Microstructure and Magnetic Properties of Au-doped Finemet-type Alloy

In this report, we demonstrate a comprehensive analysis of the effects of Au addition on the microstructure and magnetic properties of Fe 73.5 Si 13.5 B 9 Nb₃Au₁ Finemet-type alloy. It was found that the as-quenched alloys were the amorphous state and turned into nanocrystalline state under heat treatments. The DSC analysis indicates that the sharply exothermal peak corresponding to the crystallization of the α-Fe(Si) was observed at 547- 579℃ depending on the heating rates, which is little higher than that of original Finemet (542-570℃, respectively). Besides, the thermomagnetic result confirmed that the full substitution of Cu by Au with the single phase structure in the M(T) curve along cooling cycle. Ultrasoft magnetic properties of the nanocrystallized samples were significantly enhanced by the proper annealing such as the increase of permeability and the decrease of the coercivity. The optimum annealing condition was found at the annealing temperature of 540℃ and the increase of the annealing time up to 90 min.

Super - giant Magneto - Impedance Effect of a LC - resonator Using a Glass - Coated Amorphous Microwire

A new discovery of the super-giant magneto-impedance (SGMI) effect was found out in a LC-resonator consisted of a glass-coated amorphous Co_(83.2)B_(3.3)Si_(5.9)Mn_(7.6) microwire. The measurement was carried out at high frequency range from 100 ㎒ up to 1 ㎓ of an ac-current flowing along the wire and at varying axial dc-magnetic field in its range of ±120 Oe. The wires, about 16 ㎛ in diameter, were fabricated by a glass-coated melt spinning technique. The shape of the impedance curves plotted vs. a dc-field is changing dramatically with the frequency. The phase angle was also strongly dependent on this field. The external dc-magnetic field changes the circumferential permeability as well as the penetration depth, both in turn change the impedance of the sample. The drastic increments of SGMI at high frequency can be understood in terms of the LC-resonance phenomena. The sudden change of the phase angle, as large as 180°, evidenced the occurrence of the resonance at a given intensity of the external dc-field. The maximum ratio of SGMI reached in the experiment by precise tuning frequency equals 450,000% at the frequency of around 551.9075 ㎒.

Effects of Saccharine N-Propane Sulfonate on the Microstructures, Magnetic Properties, and Magnetoimpedance of Electroplated Ni – Fe Permalloy Thin Films

We have studied the effects of an organic additive, saccharine N-propane sulfonate, on the microstructures, magnetic properties, and magnetoimpedance of electroplated Ni-Fe Permalloy thin films. Compared to thin films prepared with a pure inorganic electrolyte, the Ni-Fe Permalloy thin films electroplated with electrolytes containing the additive have different crystalline orientation, grain size, surface roughness, coercivity, permeability, and magnetoimpedance. There is a strong correlation between the observed structural changes and the changes in the magnetic properties, such as in the coercivity and permeability. The changes are also dependent on the structure of the electroplating cells. By using an appropriate plating cell, the coercivity can be reduced from 0.36 to 0.08 Oe. These changes in the magnetic properties result in an increase in the magnetoimpedance by 31%.