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1

The effect of axial dc-field on transverse permeability in Co-based metallic glass ribbons

Lachowicz H. K., Kuźmiński M., Yu S. C.

Materials Science

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2003

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Vol. 21, No. 1

123-132

EN

A simple geometrical model is proposed. This model allows to calculate the penetration depth and the mean transverse permeability in magnetic elements of a rectangular cross-section which are used to study the giant magnetoimpedance effect (GMI). As an instance of the use of this model, both the mentioned quantities were calculated for the Co-based metallic glass ribbon using the experimental data obtained for the Co-based metallic glass ribbons. Their evolution with the applied axial dc-field at various frequencies of the ac-current, flowing along the ribbon, is presented. A comparison of the experimental data with those calculated by the model, shows that the latter gives only a qualitative approximation of the measured dependencies.

2

Large magnetocaloric effect in perovskite manganites: magnetic entropy changes above 300 K

Phan M. H., Yu S. C., Ulyanov A. N., Lachowicz H. K.

Materials Science

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2003

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Vol. 21, No. 1

133-139

EN

We present here, the results of an investigation of the large magnetic entropy change, M S D , above 300 K in a series of La0.65Sr0.35MnO3, La0.6Sr0.2Ca0.2MnO3, La0.6Sr0.2Ba0.2MnO3, La0.7Ba0.3MnO3 and La0.7Ba0.24Ca0.06MnO3 perovskite manganites. Among the studied compositions, La0.6Sr0.2Ba0.2MnO3 exhibits a highest value of 2.26 J/kg/K for |ASMmax| at the Curie temperature, TC = 354 K, when the field is changed from 0 to 10 kOe. The adiabatic temperature change, ATad, of this sample is ~ 1.1 K and ~ 4.95 K in the fields of 10 kOe and 50 kOe, respectively. Since the large magnetocaloric effect was found in the present materials with above 300 K Curie temperature, these materials seem to be attractive for above room temperature magnetic refrigeration applications.

3

High frequency magneto-impedance effect in glass-coated amorphous Co83.2 B3.3 Si5.9 Mn7.6 microwires

Lee H., Kim Y. S., Yu S. C.

Materials Science

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2003

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Vol. 21, No. 1

115-121

EN

The measurements of the giant magneto-impedance (GMI) were carried out in the amorphous Co83.2B3.3Si5.9Mn7.6 micro-wires at high frequency range from 100 MHz up to 1 GHz of an accurrent flowing along the wire and at varying axial dc-magnetic field in its range of š120 Oe. The wires, about 15žm 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 maximum value of GMI, around 250%, was reached at the frequency of about 500 MHz. 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 increments of GMI 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.

4

The effects of sintering additives on sinterability and microwave properities of yttrium iron garnet

Kim W. T, Song Y. Y., Yu S. C., Park J. R., Lee S. S.

Electron Technology

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1998

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Vol. 31, No. 1

121-128

EN

The effects of small addition of either Bi₂O₃ or a mixture of CuO + B₂O₃ on sinterability and microwave properties of yttrium iron garnet (YIG), prepared using a conventional ceramic method, have been studied by means of scanning electron microscopy, X-ray diffractometry, magnetometry and ferromagnetic resonance experiments. Sintering temperature for YIG could be reduced by about 50 K or 150 K by adding small amount of Bi₂O₃ or a mixture of B₂O₃ + CuO. Saturation magnetization and Curie temperature of YIG samples were almost independent of the addition of sintering additives. YIG specimens sintered at 1623 K with 1.5 wt% Bi₂O₃ and YIG sintered at 1523 K with 1.0 wt% of B₂O₃ + CuO mixture showed ferromagnetic resonance linewidth DH of 62 Oe and 58 Oe, respectively, compared with 65 Oe in pure YIG specimen sinterded at 1673 K for 2 hrs.

5

Surface magnetic anisotropy of Co Hf thin films

Lim W. Y., Baek J. S., Kim Y. Y., Lee S. J., Yu S. C., Lee S. H.

Electron Technology

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1998

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Vol. 31, No. 1

60-64

EN

In order to investigate the effect of Hf content and the thickness of Co₁₀₀₋xHfx (x=16,24, 32 at.%) films we observed the absorption lines of spin wave resonance through the ferromagnetic resonance (FMR) measurement. One volume spin wave mode and surface spin wave models were observed for all the samples because the surface anisotropy constants of both sides of the films areless than zero. When the annealing temperature for Co84Hf16 film increased up to 225°C the surface magnetic anisotropy constant Ks2 of the film-substrate interface decreased from -0,07 erg/cm² to -0.32 erg/cm² and the Ks1 constant Ks2 of the film-air interface varied from 0.18 erg/cm² to -47 erg/cm². In Co76Hf24 film Ks2 decreased a little from -0.31 erg/cm² to -0.41 erg/cm² and Ks1 decreased rapidly from -0.19 erg/cm² to-0.60 erg/cm². In genearal it is shown that the surface anisotropy at the film-air interface is very sensitive to Hf content and annealing temperature. This result is due to the increase of Co content caused by oxidation of Hf atoms near the film-air interface during low temperature annealing (150~175°C) and the diffusion of Co atoms during high temperature annealing (200~220°C).

6

Structural and magnetic properties of the Co-sputtered Fe-ceramic thin film

Yu S. C., Kim W. T, Han S. H., Kim H. J.

Electron Technology

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1998

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Vol. 31, No. 1

102-107

EN

The structure and magnetic properties of Fe-ceramics (Si₃N₄, Al₂O₃) thin films fabricated gy an rf magnetron co-sputtering technique were studied by X-ray diffractometry, magnetometry and electrical resustivity measurement. The concentration of Fe in the film decreases linearly with the area fraction of ceramic pieces on the target. As the area fraction of the ceramic pieses increases, the phase of thin film changes from bcc crystaline phase to amorphous phase, and the magnetization of the film decreased due to the decrease of Fe content and also due to the decreased of grain size. The electrical resistivity of thin films increases significantly with decreasing Fe content. Saturation magnetization of co-sputtered thin films could be explained by a mixture of two types of particles showing paramagnetism and ferromagnetism.

7

Anisotropy inhomogeneity of soft magnetic thin films

Jang P. W., Choi T. W., Yu S. C.

Electron Technology

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1998

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Vol. 31, No. 1

65-69

EN

Anisotropy inhomogeneity of rf sputtered permalloy thin films was measured using the TBP method. Angular distribution function showed the Lorentz distribution because of a long taol to high Hk. With increasing film thicknees, both the angular and magnitude anisotropy dispersion increased. This could be attributed to the increase of grain size and local anisotropy, as suggested by the Hoffmann ripple theory. However, the complex permeability calculated with both anisotropy inhomogeneity and eddy current effects taken into account did not match well the measured permebility.