Showing papers by "Seong-Cho Yu published in 2001"

Permeability and giant magnetoimpedance in Co69Fe4.5X1.5Si10B15 (X=Cr, Mn, Ni) amorphous ribbons

Abstract: The magnetoimpedance (MI) has been measured in the amorphous ribbons of the soft ferromagnetic alloy Co69Fe4.5X1.5Si10B15 (X=Cr, Mn, Ni) as functions of frequency (f ). For all of the three samples, at low frequency, f⩽5 MHz, the MI ratio increases with increasing frequency, but the MI ratio decreases at high frequency, f⩾5 MHz. The MI profiles are not changed at low frequency regions of f⩽1 MHz in the amorphous ribbons. The MI ratio at high frequency of f=5 MHz becomes 57% in Co69Fe4.5Cr1.5Si10B15, but the MI ratio becomes 30% in Co69Fe4.5Mn1.5Si10B15 and Co69Fe4.5Ni1.5Si10B15. The MI ratio at f=10 MHz becomes 45% in Co69Fe4.5Cr1.5Si10B15 and the MI ratio becomes 23% in Co69Fe4.5Mn1.5Si10B15 and Co69Fe4.5Ni1.5Si10B15, respectively. The maximum values of field sensitivity are 2.7(X=Cr), 2.5(X=Mn), 2.2(X=Ni)%/Oe for f=5 MHz.

Laser annealing effect of giant magneto-impedance in amorphous Co66Fe4Nib14Si15 ribbon

Abstract: The magneto-impedance (MI) profiles of Co66Fe4NiB14Si15 amorphous ribbon varied sensitively with the annealing energy of the pulsed Nd:YAG laser, reflecting the change of anisotropy field which determines the field dependence of transverse permeability Laser annealing effect of giant magneto-impedance (GMI) in amorphous Co66Fe4NiB14Si15 ribbon are discussed in terms of laser annealing energy The pulsed Nd:YAG laser was pumped with Kr-lamp and consisted of a Nd:YAG rod of φ 5 mm ×70 mm (AR coated plane/plane), a full mirror and output coupler (30% transmission) The wavelength was 1064 μm and the pulse width was 220 μs The GMI ratio increases with annealing energy showing largest value at 136 mJ/pulse (peak power is ∼620 W) The GMI ratio decreases with further increment of annealing energy The decreasing Hk with the annealing energy is ascribed to the increase of magnetic softness, while the increasing Hk and the decreasing MI ratio for the further increment of annealing energy could be due to the microstructural change by the laser annealing

Annealing and neutron irradiation effects on the magnetic properties of Fe73.5Cu1Nb3Si13.5B9

Abstract: The annealing and neutron irradiation effects on the magnetic properties of amorphous Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloy were investigated. The sample was exposed by fast (4.85×10 16 n f cm 2 ) and thermal (8.01×10 18 n th cm 2 ) neutrons at the temperature of 473 K. The complex magnetic permeability spectra changed with the ac field amplitude, reflecting the contribution of wall motion and rotational magnetization in as-quenched sample. The neutron irradiation sample showed the drastic decrease of permeability from wall motion but the increase of permeability from rotational magnetization, compared to those in as-quenched and annealed samples at 473 K. As a whole, dc permeability in neutron irradiated sample was larger than that of the as-quenched sample. The measurement of hysteresis loop showed the increase of magnetic softness after the neutron irradiation, but saturation magnetization was insensitive to the neutron irradiation. These results indicated that magnetic softness was improved by the enhancement of rotational magnetization

Bias-current effect on giant magnetoimpedance in Co-based amorphous microwire

Abstract: The giant magnetoimpedance (GMI) effect has been measured in Co 83.2 B 3.3 Si 5.9 Mn 7.6 amorphous microwire as a function of direct current (dc)-biased current and measuring frequency, f . The GMI profile has a single peak for f ⩽5 MHz, and two peaks at higher frequency. The maximum GMI ratio increases continuously with frequency up to 45% at 10 MHz. The influence of superimposed dc biasing is shown to result in asymmetrical GMI as well as in a shift of the axial hysteresis loop. Both effects are interpreted in terms of the relative contribution of domain wall and rotational processes to the transverse susceptibility.

EXAFS Study for Mechanical Alloyed Fe80C20.

Abstract: The local structure has been examined by the extended X-ray absorption fine structure (EXAFS) for metastable Fe 80 C 20 alloys produced by the mechanical alloying process. The order between Fe atoms in the alloys decreased continuously as the process time increased. The substantial changes of the local structure appears in about 6 hours milling time and the amorphization occurs between 6 and 12 hours milling time.The magnetization was interpreted by the variation of the local structure.

Co-existing magnetic phases of nano-scaled granular Co20Cu80 alloy system

Abstract: Nano-scaled granular Co 20 Cu 80 alloy was prepared by mechanical alloying technique and the resulting powder was consolidated by hot pressing. Structural evolution and magnetization behavior were examined by using X-ray diffractometry and magnetization measurement by VSM and SQUID magnetometer. XRD results and variation of magnetization with processing time show the formation of a supersaturated fcc solid solution. Magnetization of the alloy could be interpreted as a mixture of ferromagnetic and superparamagnetic components, resulting from the non-uniform size distribution of magnetic clusters in the Cu matrix. With increasing temperature superparamagnetic component becomes the dominant contributor. Maximum MR ratio of the hot pressed specimen was about 3.3% at room temperature, under a maximum magnetic field of 10 kOe.

Effect of Highly Oriented Layer on GMR and Magnetic Properties of NiFe / Cu Thin Film Prepared by Magnetron Sputtering

Abstract: In order to investigate the effect of the interface on GMR, [NiFe(25 Å)/Cu(24 Å)]₂/Si thin film was epitaxially grown on HF-treated Si (001) substrate using a DC magnetron sputtering method. Typical GMR effects could be observed in epitaxial film with a weak antiferromagnetic exchange coupling while non epitaxial film showed unsaturated and broad MR curves probably due to inter-diffusion between NiFe and Cu layers. Ferromagnetic resonance (FMR) experiment showed two distinct absorption peaks in all films. Each peak was revealed to come from each NiFe layer with different magnetic property. In FMR measurement, very clear interface in epitaxial films could be confirmed by a lower value of line width (ΔH) and higher Ms of epitaxial film than those of non epitaxial films, respectively.