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박일우(I.-W. Park),홍영식(Y.-S. Hong),김영미(Y. M. Kim),윤혜온(H. Yoon),이경재(K. J. Lee),조성학(S. H. Cho) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.1
We have manufactured and evaluated reference samples for the use of low magnetic moment measurements. Before the measurements, SQUID magnetometers were magnetically shielded from external magnetic noise. We considered the purity including magnetic impurities, the optimum thickness, the modification method, and the shape in the preparation of the samples. Three paramagnetic polycrystaline metal plates of Ti, W, and Al with the area of 4 ㎜×6 ㎜ were prepared finally. The magnetic moments of these three samples are measured very linear up to the field of 5 T without magnetic hysteresis. The temperature deviated ratios of the magnetic moments for Ti, Al, and W from 290 K to 310 K are 0.7, 1.5, and 0.1%, respectively. The measured magnetic moments for Ti and W samples by our research team are very well agreeable with those by two SQUID magnetometers and a VSM at Quantum Design via international round robin test. The results suggest that the prepared reference samples are well suited for the use in the low magnetic moment measurement with SQUID based magnetometers.
VTE 처리된 강유전 LiNbO₃ 단결정 내의 Nd³+와 Er³+ 초미세 구조의 비등방성
박일우(I.-W. Park),조성호(S. H. Choh),김영미(Y. M. Kim),전웅(U. Chon),김상수(S. S. Kim),김원정(W. J. Kim),김봉구(B. G. Kim),손재민(J. M. Sohn) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.2
We have obtained sharp and clearly resolved ESR spectra of Nd³+ and Er³+ in vapor transport equilibrium (VTE) treated LiNbO₃ crystals, consequently have determined more accurate spin Hamiltonian parameters, than those in congruent samples. The anisotropic hyperfine structures of ¹⁴³Nd³+ and (145)^Nd³+ in the VTE-treated crystals at liquid helium temperature have been analyzed. It is proposed that both rare earth ions favor the lithium site in LiNbO₃ from the consideration of the determined anisotropic g-values.
열처리 효과에 따른 Zn0.7Mn0.3O 박막의 자기 특성 연구
김영미(Y. M. Kim),김유경(Y. Kim),윤명근(M. Yoon),박찬수(C. S. Park),이연숙(Y. S. Lee),전미선(M. S. Jeon),박일우(I.-W. Park),박용주(Y. J. Park),유종훈(Jong H. Lyou),김상수(S. S. Kim) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.4
We report on the annealing effect and ferromagnetic characteristics of Zn_(0.7)Mn_(0.3)O film prepared by sol-gel method on the silicon (100) substrate using field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry. Magnetic measurements show that Zn_(0.7)Mn_(0.3)O films exhibit ferromagnetism at 5 K revealing the coercive field of ~110 Oe for as grown sample and 360, 1035 Oe for samples annealed at 700, 800 ℃, respectively. Our experimental evidence suggests that ferromagnetic precipitates of a manganese oxide may be responsible for the observed ferromagnetic behaviors of the film.
코발트 나노 입자가 도입된 초상자성 고분자 박막의 제조 및 자성 연구
김유경(Y. Kim),윤명근(M. Yoon),김영미(Y. M. Kim),비탈리볼코프(V. Volkov),박일우(I.-W. Park),송호준(H. J. Song) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.2
Superparamagnetic properties of self-aggregated cobalt nanoparticles in the perfluorinated ion-exchange polymeric membrane (MF-4SK) prepared by ion-exchange and recovery methods were investigated by transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID) magnetometer at various temperatures. Our experimental results show that cobalt nanoparticles in MF-4SK for the concentration of 7.8×10^(19) atoms per 1g of polymer membrane exhibit superparamagnetic properties above the average blocking temperature (T_B), which is determined to be around 185 K at applied field of 500 Oe. The average particle radius of 4.0 ㎚ achieved from Langevin function fit is in good agreement with TEM observations. This experimental evidence suggests that cobalt nanoparticles in polymer film obey a single domain theory. The results are discussed in the light of current theory for the superparamagnetic behavior of magnetic nanoparticles.