Yong-Kook Kim

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.

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.

Soft Magnetic Properties of Co‐Based Amorphous Alloy by Two‐Step Cooling Method

The soft magnetic properties of Co-based amorphous Co 66 Fe 4 Ni 1 Si 15 B 14 alloy in terms of various annealing conditions have been investigated by magnetoimpedance (MI) effect and permeability ratio (PR). In order to enhance the soft magnetic properties by co-reducing internal thermal stress and magnetic ordering, we applied the furnace cooling to Curie temperature and subsequent water quenching (F&W) method, which considerably increased the initial permeability - to values 60% or 100% higher than in the only furnace-cooled (FC) or water-quenched samples, respectively. However, the MI and PR results show that the FC sample is softer than the F&W sample at high frequencies.

Temperature dependence of the magnetoimpedance effect in nanocrystalline Fe84Zr7B6Cu1Al2 alloy

Abstract The nanocrystalline Fe 84 Zr 7 B 6 Cu 1 Al 2 alloy was annealed at 450 and 550°C for 1 h to achieve the ultra-soft magnetic properties such as large magnetoimpedance ratio (MIR), the incremental permeability ratio (PR), nearly zero coercivity, zero magnetostriction, etc. The MIR and PR of the sample were measured from 100 kHz to 10 MHz in a cryogenic chamber where the temperature was varied from 10 to 300 K. The increment of MIR value is proportional to increasing temperature. The maximum PR values measured above 1 MHz remain almost temperature independent. However, the maximum PR values measured below 1 MHz show drastic increment at above 150 K due to thermal activation of magnetic domains.

Anisotropy in nanocrystalline Fe73.5Cu1Nb3Si13.5B9 wire

Soft magnetic properties of nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 wire have been investigated by magnetoimpedance ratio (MIR) and incremental permeability ratio (PR). The MI and PR measurements were carried out along the ribbon axis with longitudinal magnetic field. The MIR values increased drastically from 60% to 170% after proper thermal treatment. Annealing was performed in a vacuum for 1 h at various temperatures of 250, 350, 450, and 550 °C, respectively. Softest magnetic behavior has been observed in the samples annealed at 450°C. Annealing over 550 °C leads to decrement of MIR and PR. The shapes of MIR and PR curves have shown the decrement of anisotropy field and also the PR curves have shown the change of anisotropy field from transverse to longitudinal direction as the annealing temperature increases.

Magnetoimpedance Effect in Nanocrystalline Fe91.5-xZr7BxCu₁Al0.5 (x = 2, 4, 6, 8) Alloys

The magnetoimpedance of Fe_(91.5-x)Zr_7B_xCu₁Al_(0.5) (x = 2, 4, 6, 8) alloys has been measured to investigate the influence of structural changes in the nanocrystallization process after thermal treatment. Annealing was performed at temperatures of 350℃, 450℃, and 550℃ for 1 hour in a vacuum. Ultra soft magnetic behavior was observed in the samples annealed at 550℃. The magnetoimpedance ratio and the longitudinal permeability ratio coincided with the softness of the magnetic properties of the thermally treated samples.

Soft magnetic properties of nanocrystalline Fe75−xCoxZr8Nb2B15 (x=5, 10, 15) alloys

Abstract Soft magnetic properties of melt spun Fe 75− x Co x Zr 8 Nb 2 B 15 alloys have been investigated in terms of partial nanocrystallization by proper thermal treatment. The spin wave stiffness constant, D , was estimated from the temperature dependence of the magnetization at low temperature. The Curie temperature, T c , is enhanced with increasing Co content. In particular, D / T c , which measures the range of the exchange interaction, are roughly independent of Co concentration. The incremental permeability ratio (PR) shows the drastic changes of soft magnetic properties as a function of annealing temperatures. Soft magnetic samples are obtained from the sample with x =10 annealed at 500°C and the sample with x =15 annealed at 400°C as clearly distinguishable from the sharpness of PR as well as its magnitudes.