Showing papers by "Seong-Cho Yu published in 1998"

Enhanced anisotropic nature of HgBa 2 Ca 3 Cu 4 O 1 0 + δ

Abstract: Reversible magnetization of grain-aligned ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{10+\mathrm{\ensuremath{\delta}}}$ with the external magnetic fields of 1 T $l~Hl~$ 5 T parallel to the $c$ axis has been measured. The application of the model of Hao et al. [Phys. Rev. Lett. 67, 2371 (1991); Phys. Rev. B 43, 2844 (1991)] to our data gives the anomalous temperature dependence of the Ginzburg-Landau parameter $\ensuremath{\kappa}(T)$, i.e., the increase of $\ensuremath{\kappa}$ with $T$, in the entire reversible region 81 K $l~Tl~$ 100 K. This implies that the thermal distortions of the vortices are not negligible even far below ${T}_{c}$ and thus the system is a highly anisotropic. This is supported by the two-dimensional scaling behavior of the magnetization in the critical region. From the model of Hao et al. we obtained various superconducting parameters such as the critical fields, the coherence length, and the penetration depth. In particular, the zero-temperature penetration depth ${\ensuremath{\lambda}}_{\mathrm{ab}}(0)$ is estimated to be 157 nm, which is the smallest of the Hg-based superconductors. We infer that this is due to the large hole density within the ${\mathrm{CuO}}_{2}$ plane.

The magnetization study of melt-spun ribbons of B containing TbFe2 alloys

Abstract: We have carried out the magnetization study of melt-spun ribbons of (Tb033Fe067)1−xBx (x=0, 002, 005, 01, and 015) alloys The temperature dependence of magnetization was measured using a superconducting quantum interference device and a vibrating-sample magnetometer during heating from 5 to 800 K, with an applied field of either 10 or 50 kOe The present study shows the existence of noncollinear magnetics structures From an analysis of the approach to saturation magnetization, the average magnetic moment μa, random anisotropy field Hr, and local random anisotropy constant KL have been extracted It is found that μa decreases from 168 (x=0) to 133 μB (x=015) and KL increases with increasing B concentration This result suggests that the addition of B seems to increase the random anisotropy and hence to decrease the magnetic order, resulting a sperimagnet with large spread angle

Structure and magnetic properties of a Fe–Zr–N thin film

Abstract: Fe–Zr–N thin films were deposited in an argon and nitrogen mixed atmosphere using a rf magnetron reactive sputtering apparatus at room temperature. The x-ray diffraction pattern of the Fe76Zr8N16 thin film obtained at room temperature indicates that the as-sputtered film consists of amorphous and crystalline phases. The mixed structure of the sample was also confirmed by the temperature dependence of the saturation magnetic flux density. The as-sputtered film exhibited soft magnetic properties with a saturation magnetic flux density of 1.1 T and effective permeability of 1400 or more at 1 MHz. The film also showed good thermal stability, sustaining the effective permeability of 3000 at temperatures up to 550 °C. The film annealed in a magnetic field of 500 Oe at 450 °C showed a permeability of 2200 or more up to 40 MHz. The conventional Mossbauer spectrum of the kapton substrate sample obtained at room temperature could be fitted by a mixture of three kinds of six-line hyperfine splittings.

The Magnetization Study of Melt-Spun TbFe/sub 2/-B Alloy with Large Magnetostriction

Abstract: 28 1 FQ-15. MAGNETIC AND STRUCTURAL PROPERTIES OF COMMERCIAL Smz(Co,Fe,Cu.Zr),,-BASED MAGNETS. Xinhe Chen. Chaoying Ni. and George Hadjipanayis (Dept. of Phys. and Astronomy. Univ. of Delaware, Newark DE 19716-2570) Precipitation hardened Sm?(Co.Fe.Cu,Zr)l,-based magnets are very promising candidates for high temperature applications. A systematic investigation of magnetic and structural properties of these magnets is needed. in order to further improve the high temperature performance of these magnets at temperatures beyond 400°C. Several commercial Sin(Co,Fe.Cu.Zr) ,-based magnets were used to study and understand the temperature dependence af magnetic properties up to 500’C. SQUID and VSM were used to obtain the hysteresis loop^ and the initial magnetization curves and to determine the coercivity and remancnce. Magnetic viscosity measurements were carried out for two typical specimens, showing that the magnet with higher coercivity above 400°C has a higher magnetic viscosity coeficient. This magnetal so shows a typical pinning-type initial magnetization curve at room temperature. The as-received magnets have the Th?Nil, rhombohedral structure. Curie temperatures of all specimens are above 800°C. There is only one single value of Curie temperature for each specimen. Temperature dependences of coercivities show that the temperature coefficient of coercivity. p, is a critical factor for high coercivity at high temperature. Most of the samples with Z-7.7 showed a p= -0.2 %/K. which resulted in a H, of about 3 kOe at 350°C. However, a magnet with Z = 7 gave a p of -0.16 %IK. resulting in a H,.-6 kOe at the same temperature. TEM studies show similar microstructures in all samples consisting of a cellular structure and lamellar precipitates. A statistical analysis was performed on the cellular structure and lamellar precipitate. A comparison between the two samples indicates that higher cell density contributes to the hi;h temperature coercivity. FQ-16. MAGNETIC PROPERTIES OF Pr3(FeaTi)29 AND Nd3(Fe,Ti)29 SINGLE CRYSTALS. W. Mendoza and S. A. Shaheen (Dept. of Phys. and Ctr. for Mater. Res. and Technol. (MARTECH). Florida State Univ.. Tallahassee. FL 32306-4000) Single crystals of above mentioned 3 9 9 materials have been grown by Czochralski technique in a tri-arc furnace. The crystals are typically 2-3 nim in diameter and 10-15 mm in length. The crystals were cut approximately perpendicular to the growth axis and then were smoothed for x-ray diffraction studies. X rays revealed a single peak at about 28=44.3-44.6 degree corresponding to a (2 2 -4) orientation according to the 3: 29 structure. Magnetic data indicate a small magnetic anisotropy at room temperature, in agreement with the published results on aligned powder samples’. Detailed results will be presented and compared with polycrystalline results. ‘C. D. Fuerst. F. E. Pinkerton. and J. F. Herbst. J. Magn. Magn. Mater. 129 (1994) LI 15. FQ-17. THE MAGNETIZATION STUDY OF MELT-SPUN TbFe,-B ALLOY WITH LARGE MAGNETOSTRICTION. Kyeong-Sup Kim. Seong-Cho Yu (Dept. of Phys.. Chungbuk Nat’l Univ.. Cheongju, 361-763 Korea). Sang-Rok Kim. and Sang-Ho Lim (Mag. Mat. Lab., Korea Inst. Sci. & Tech., Seoul. 130-650 Korea) We have carried out the mapnetization study of melt-spun TbFe,-B alloys with large magnetostriction. Recently, grain refinement in TbFe,-B alloys has heen achieved by a partial crystallization of a melt-spun amorphous phase. The alloy with nanocrystalline grain structure exhibited better magnetostrictive characteristics than bulk TbFe, alloy. More recently. i t was shown by the present authors for magnetostrictive by Fe-based alloys that homogeneous and ultrafine grains were obtained even in the as-spun state’. We therefore find i t appropriate to investigate in detail the magnetic properties of melt-spun (Tbo.~~Feo6;),-,B, (x=0. 0.2, 0.05. 0.1, 0.15) alloys. Temperature dependence of the magnetization of samples were measured using a SQUID and VSM during heating from 5 to 800 K. with applied field of either I O kOe or SO kOe. Unusual variation of magnetization behavior measured at 10 kOe were observed in all specimens. The increase of magnetization with increasing temperature at low temperature seems to be related with the competing interaction between Fe and To. With increasing temperature. magnetization decreases monotonically, which is similar to ferromagnetic behavior with an external magnetic field of 50 kOe. In order to get the intrinsic magnetic properties we analyzed the relationship between exchange energy and magnetic anisotropy using the mean field theory and random anisotropy model. The variation of the magnetic properties are discussed and compared with the composition of materials. ‘S. H. Lim, S. R. Kim, and H. J. Kim. IEEE Trans. Magn., 32, 4770

Annealing Effect of Local Anisotropy Field in Amorphous Co66Fe₄Ni₁B₁₄Si15 Ribbon

Abstract: The magneto-impedance (MI) has been measured in the annealed Co_(66)Fe₄Ni₁B₁₄Si_(15) amorphous ribbon for the evaluation of anisotropy field MI at the frequency of 10 ㎒ is related to the transverse permeability from rotational magnetization depending on the local anisotropy field MI varies sensitively with the annealing temperature, reflecting the change of anisotropy field distribution The local anisotropy fields evaluated from MI profiles are discussed in terms of the magnetic softness and microstructural change by the annealing