Showing papers by "Seong-Cho Yu published in 1997"
TL;DR: In this article, the influence of exchange energy and magnetic anisotropy on the magnetic properties of nanocrystalline materials has been studied and the best soft magnetic properties were observed annealed at 650°C for the smallest magneto-crystalline anisotropic constant (K1) of about 1.40×104´erg/cm3.
Abstract: We have studied the influence of exchange energy and magnetic anisotropy on the magnetic properties of nanocrystalline materials. Amorphous ribbons of composition Fe88Zr7B4Cu1 have been annealed between about 500 and 700 °C. Temperature dependence of magnetization was carried out and nanocrystallized magnetic entities were investigated using the mean field theory and random anisotropy model obtained ferromagnetic correlation length and magneto-crystalline anisotropy constant. The best soft magnetic properties were observed annealed at 650 °C for the smallest magneto-crystalline anisotropy constant (K1) of about 1.40×104 erg/cm3. We obtained average magnetic anisotropy of 0.81 erg/cm3 which is almost negligible compared with K1 at an annealing temperature of 650 °C. The local magneto-crystalline anisotropy is randomly averaged out by strong exchange interaction so that this mechanism provides the basis for the good soft magnetic properties.
5 citations
TL;DR: In this article, high-field magnetization with external magnetic fields parallel to the c-axis has been measured in high-quality YBa2Cu4O8 single crystal, and the thermodynamic parameters such as upper critical field slope −dHc2/dT=1.2 T/K near Tc, penetration depth λab(0)=1943 A, and coherence length ξab( 0)=21.7 A were extracted.
Abstract: High-field magnetization with external magnetic fields parallel to the c-axis has been measured in high-quality YBa2Cu4O8 single crystal. The fluctuation-induced magnetization above Tc and a crossover of magnetization curves M(T) at T*=77.4 K were clearly observed for various magnetic fields, and analyzed by the high-field scaling law and the vortex fluctuation theory for three-dimensional systems. In the reversible temperature region, the magnetization is well described by the model of Hao et al. [Phys. Rev. B 43, 2884 (1991)]. From this analysis, the thermodynamic parameters such as upper critical field slope −dHc2/dT=1.2 T/K near Tc, penetration depth λab(0)=1943 A, and coherence length ξab(0)=21.7 A were extracted.
5 citations
01 Apr 1997
TL;DR: In this article, the structure and magnetic properties of Fe-Si/sub 3/N/sub 4/ thin films fabricated by a co-sputtering technique were studied by X-ray diffractometry and magnetometry.
Abstract: The structure and magnetic properties of Fe-Si/sub 3/N/sub 4/ thin films fabricated by a co-sputtering technique were studied by X-ray diffractometry and magnetometry. With increasing area fraction of Si/sub 3/N/sub 4/ pieces on the Fe target, magnetization of the films decreased due to reduced Fe content and reduced grain size of the bcc crystalline phase. The temperature dependence and field dependence of magnetization of co-sputtered thin films can be explained by a mixture of two types of particles showing paramagnetism and ferromagnetism.
5 citations
TL;DR: In this article, the effects of milling time and heat treatment on local structural changes during mechanical alloying Fe40Co10Cu50 have been investigated by means of x-ray diffraction (XRD), neutron diffraction technique, vibrating sample magnetometer, and Mossbauer spectroscopy.
Abstract: The effects of milling time and heat treatment on local structural changes during mechanical alloying Fe40Co10Cu50 have been investigated by means of x-ray diffraction (XRD), neutron diffraction technique, vibrating sample magnetometer, and Mossbauer spectroscopy. Mossbauer spectroscopy showed that two kinds of magnetic phases coexist in the mechanically alloyed powder, which is in agreement with XRD and neutron diffraction study. One is corresponding to α-Fe and the other is a new magnetic phase formed during mechanical alloying. With increasing processing time, the new magnetic phase becomes more ordered and dominant. Mossbauer spectrum from the annealed sample consists of ferromagnetic component with a hyperfine field of 36.2 T and a paramagnetic component.
4 citations
TL;DR: In this article, the effect of vortices in pristine and iodine-intercalated Bi 2 Sr 2 CaCu 2 O 8 single crystals were studied in magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis.
Abstract: Copyright (c) 1997 Elsevier Science B.V. All rights reserved. Vortex fluctuation effects in pristine and iodine-intercalated Bi 2 Sr 2 CaCu 2 O 8 single crystals were studied in magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis. We found that iodine-intercalated specimen showed strong positional fluctuations of the vortices even far below the transition temperature due to the reduction of the interlayer coupling. Also. we obtaind various thermodynamic parameters (H r (0), H r2 (0), λ ab (0), and ξ ab (0)) using thc Hao-Clem and other related models.
2 citations
TL;DR: In this article, a strong vortex fluctuation effect was clearly observed and the magnetization is well described by the vortex fluctuations model, and the penetration depth λ ab (0) = 1583 A and the effective interlayer spacing s = 44.6 A were estimated.
Abstract: Reversible magnetization with the external magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c -axis has been measured for the grain aligned HgBa 2 Ca 3 Cu 4 O 10+δ . A strong vortex fluctuation effect was clearly observed and the magnetization is well described by the vortex fluctuation model. From this analysis, the penetration depth λ ab (0) = 1583 A and the effective interlayer spacing s = 44.6 A were estimated. However, the value of s is significantly larger than the lattice parameter c = 19 A, which is different from the prediction of the vortex fluctuation model. From the model on superconducting fluctuations proposed by Koshelev, in which not only the critical fluctuations at the lowest Landau level but also the Gaussian fluctuations at higher Landau levels were considered, the different value of s = 15.4 A was obtained.
1 citations
Journal Article•
TL;DR: In this article, the temperature dependence of magnetization for amorphous ribbons was measured by a SQUID and a VSM from 5 K to 700 K under an external field of 10 kOe.
Abstract: We report the salient features of the magnetic properties of amorphous TM_(70)Cr_5Si_(10)B_(15) (TM=Fe, CO, Ni) alloys. The temperature dependence of magnetization for amorphous ribbons were measured by a SQUID and a VSM from 5 K to 700 K under an external field of 10 kOe. Except TM_(70)Cr_5Si_(10)B_(15) that shows a paramagnetic behaviour, both Fe and Co based amorphous alloys show a typical ferromagnetic thermo-magnetization curves. For these two ferromagnetic alloys, the saturation magnetization in the temperature range from 5 K to about 0.4 Tc can be descrived by the Bloch relation, Ms (T) = Ms(0) [1-BT^(3/2)-CT^(5/2)]. The spin wave stiffness constants and the range of exchange interaction were analyzed from the magnetization behaviour. The variation of the magnetic properties are discussed and compared with the composition of the alloys.
1 citations
01 Apr 1997
TL;DR: In this paper, local structural change in mechanically alloyed Fe/sub x/Co/sub 50-x/Cu/Sub 50/ powders has been investigated by Mossbauer spectroscopy and X-ray diffractometry at room temperature.
Abstract: Local structural change in mechanically alloyed Fe/sub x/Co/sub 50-x/Cu/sub 50/ (x=10, 20, 30, 40 and 50) powders has been investigated by Mossbauer spectroscopy and X-ray diffractometry at room temperature. Mossbauer spectra from mechanically alloyed Fe/sub x/Co/sub 50-x/Cu/sub 50/ samples consist of three different subspectra: a sextet, a broad sextet and a doublet corresponding to an /spl alpha/-Fe phase, to a disordered ferromagnetic phase of fcc solid solution, and to a non-ferromagnetic phase, respectively. With increasing processing time, the disordered ferromagnetic phase becomes dominant, indicating a formation of fcc solid solution during mechanical alloying. With increasing Co content, the hyperfine field of the disordered magnetic phase increases from about 20 to 25 T.
TL;DR: In this paper, the authors explored explicit dynamic finite-size scaling in the time-dependent correlation functions for the two-dimensional classical XY model and showed that the model is critical for all temperatures below TKT.
Abstract: Explicit dynamic finite-size scaling in the time-dependent correlation functions for the two-dimensional classical XY model is explored. The dynamic scaling method, proposed by us previously, is utilized for finding the time scaling variables of the model. It shows nontrivial dynamic finite-size scaling behavior near and below TKT for the total spin correlation function. Since the model is critical for all temperatures below TKT, the time scaling exponent is markedly different from that of the three-dimensional classical XY model at short times. There also appears to be another dynamic scaling region with a different time scaling exponent at T⩽TKT for a fairly wide intermediate time interval.
01 Jan 1997
TL;DR: In this paper, local structural change in mechanically alloyed Fe,Cos.~Cuso powders has been investigated by Mossbauer spectroscopy and X-ray diffractometry at room temperature.
Abstract: Local structural change in mechanically alloyed Fe,Cos~.~Cuso (x=10, 20, 30, 40 and 50) powders has been investigated by Mossbauer spectroscopy and X-ray diffractometry at room temperature. Mossbauer spectra from mechanically alloyed Fe,Coso.lCusa samples consist of three different subspectra : a sextet, a broad sextet and a doublet corresponding to an u-Fe phase, to a disordered ferromagnetic phase of fcc solid solution, and to a non-ferromagnetic phase, respectively. With increasing processing time, disordered ferromagnetic phase becomes dominant, indicating a formation of fcc solid solution during mechanical alloying. With increasing CO content, hyperfine field of the disordered magnetic phase increases from about 20 to 25 T.