Wan-Shik Cho

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.

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.

The effect of anisotropy in Co/sub 66/Fe/sub 4/Ni/sub 1/B/sub 14/Si/sub 15/ ribbon on the transverse incremental permeability and magnetoimpedance

The transverse incremental permeability and magneto-impedance effects in amorphous Co/sub 66/Fe/sub 4/Ni/sub 1/B/sub 14/Si/sub 15/ ribbons treated with various annealing and etching conditions have been investigated in conjunction with their magnetic anisotropy. The shape and the depth of double peaks in magneto-impedance ratio (MIR) and transverse permeability ratio (TPR) curves show the existence of the uniaxial magnetic anisotropy. The direction of magnetic anisotropy in samples annealed under magnetic field was induced parallel to their magnetic field. The direction of magnetic anisotropy in samples annealed without the magnetic field has changed ribbon to width direction. The surface etching of an as-quenched sample helps to orient the magnetic anisotropy to the ribbon axis. The maximum values of MIR and TPR depend on the magnetic softness rather than the direction of magnetic anisotropy. However, the shapes of MIR and TPR curves strongly depend on their uniaxial magnetic anisotropy.

Annealing effect on the longitudinal and transverse incremental permeability in FeSmO thin films

The transverse permeability ratio (TPR) and longitudinal permeability ratio (LPR) as a function of an external field of FeSmO films have been investigated in conjunction with thermal treatment. The FeSmO films were prepared by the RF magnetron sputtering method in Ar atmosphere. The film annealed at 500°C has the maximum value of the incremental permeability ratio (PR) due to the ultrasoft magnetic materials. The LPR curve shows the single-peak pattern, and the TPR curve shows the double-peak pattern indicating the existence of the magnetic anisotropy effect. The magnetic anisotropy and the magnitude of the incremental permeability are strongly dependent on the magnetic softness due to the annealing. The large changes of LPR and TPR in low external fields can be useful for the evaluation of the magnetic softness as well as the magnetic sensor applications.

Microstructure and Magnetic Properties of CoFeHfO Rich Nanocrystalline Thin Films Application for High Frequency

Nanocrystalline CoFeHfO thin films have been fabricated by RF sputtering method. Co52Fe23Hf10O15 thin film is observed, exhibit good magnetic properties with magnetic coercivity (Hc) of 0.18 Oe; anisotropy fild (Hk) of 49 Oe; saturation magnetization (4лMs) of 21 kG, and electrical resistivity (ρ) of 300 01cm. The frequency response of permeability of the film is excellent. The effect of microstructure on the electrical and magnetic properties of thin film was studied using X-ray diffraction (XRD) analysis and conventional transmission electron microscopy (TEM). The results showed that excellent soft magnetic properties were associated with granular nannoscale grains of α-CoFe and α-Co(Fe) phases.

Effect of O2 partial pressure on magnetic properties of alloys CoFe-rich nanocrystalline thin films

Alloys of CoFe-rich magnetic films are well known as typical soft magnetic alloys. They are used for many kinds of electric and electronic parts such as magnetic recording heads, transformers and inductors. In order to get superior soft magnetic properties of the CoFe-based nanocrystalline thin films, the effect of O2 partial pressure on magnetic properties of Co-Fe-Hf-O nanocrystalline thin films have been investigated. It is found that the soft magnetic properties and electrical property of these films show a dependence on the partial pressure of reactive gases, which presumably changes the microstructure of the films and related magnetic anisotropy. With optimal conditions, thin film exhibit excellent soft magnetic properties: saturation magnetization (4πMs) of 21 kG, magnetic coercivity (Hc) of 0.18 Oe, anisotropy field (Hk) of 49 Oe, and an electrical property is also shown to be as high as 300 μcm. The combination of high 4πMs and relatively high Hk in these films are believed to be partly responsible for the excellent ultra-high-frequency behavior

Excellent Magnetic Properties of Co 53 FE 22 Hf 10 O 15 Thin Films

Nanocrystalline CoFeHfO thin films have been fabricated by RF sputtering method. It is shown that the CoFeHfO thin films possess not only high electrical resistivity but also large saturation magnetization and anisotropy field. Among the composition investigated, Co?₃Fe₂₂Hf₁?O₁? thin film is observed to exhibit good soft magnetic properties: coercivity (H c ) of 0.18 Oe; anisotropy fild (H k ) of 49.92 Oe; saturation magnetization (4πM s ) of 15.5 kG. The frequency response of permeability of the film is excellent. The excellent magnetic properties of this film in addition of an extremely high electrical resistivity (r) of 185 μ㎝ make it ideal for uses in high-frequency applications of micromagnetic devices. It is the formation of a peculiar microstructure that resulted in the superior properties of this film.

Soft magnetic properties of FeSmO thin films

The magnetic properties of FeSmO films have been investigated in conjunction with thermal treatment. The FeSmO films were prepared by the RF magnetron sputtering method in Ar atmosphere. The film annealed at 500°C had the good soft magnetic properties due to the grain growth of α-Fe.