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Rhee, Ilsu,Ha, Dong-Han 한국재료학회 1995 한국재료학회지 Vol.5 No.3
가돌리늄박막의 큐리온도를 비저항의 온도에 따른 변화를 측정함으로써 결정하였다. 이비저항 실험치에서 구한 큐리온도의 값은 기존의 자화도에서 구한 큐리 온도값과 잘 일치함을 보여준다. 또한 박막의 큐리온도 실험값들은 얇은 박막일수록 큐리온도가 낮아지는 두께에 따른 변화를 잘 보여주고 있다. 유한 축척이론에 의한 분석에서 임계지수 λ 는 0.82 ± 0.15가 나왔으며 이 값은 이론치인 1.48과 일치하지 않는다. 이 사실은 다른 많은 실험에서 확인한 바와 일치하고 있다.
Ilsu Rhee,Chan Kim,Kang Yoon Kim 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
Stable iron-ferrite nanoparticles were formulated by direct coprecipitation of an aqueous solution of an iron salt and a tetramethylammonium hydroxide (TMAOH) solution. The sizes of the nanoparticles were observed to be uniformly distributed around a diameter of 5 nm. These nanoparticles also showed no coalescence in the aqueous solution over a few months. A nuclear magnetic resonance spectrometer was used to measure the spin-lattice relaxation time T1 and the spin-spin relaxation time T2 of hydrogen protons in the colloidal aqueous solution of magnetic nanoparticles over a wide range of concentration of nanoparticles from a few tenths of ppm to a few thousand ppm. The spin-lattice relaxation rate, 1/T1, was observed to directly depend on the concentration of nanoparticles over the whole nanoparticle concentration range observed. However, the spin-spin relaxation rate, 1/T2, was found to deviate from this linear behavior in the higher range of nanoparicle concentrations above about 1000 ppm. This dierent behavior of relaxation times can be explained from the fact that T2 is mainly in uenced by the inhomogeneity of the magnetic eld surrounding the hydrogen proton, and thus is more sensitive to the presence of magnetic nanoparticles than T1. Consequently, the rate of decrease in T2 increases rapidly as the number of surrounding magnetic nanoparticles increases.
Nanoparticle Concentration Dependence of the $T_1$ and $T_2$ Times of Hydrogen Proton
Ilsu Rhee,Chan Kim 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.1
The stable iron ferrite nanoparticles were formulated by using direct coprecipitation of an aqueous solution of iron salt and a tetramethylammonium hydroxide (TMAOH) solution. These superparamagnetic nanoparticles were found to have uniform sizes of about 7 nm and showed no coalescence in the aqueous solution for a few months. The relaxation times, T1 and T2, of the hydrogen protons in the aqueous solution of these nanoparticles were measured using a nuclear magnetic resonance (NMR) spectrometer at room temperature over a wide range of concentrations of the nanoparticles in the aqueous solution. The inverses of the relaxation times were observed to directly depend on the concentration of nanoparticles.
이일수(Ilsu Rhee),추교진(Gyojin Chu),이의완(Eui-Wan Lee),이상윤(Sang-Yun Lee),이종용(Chong-Yong Lee),김양수(Yaung-Soo Kim),김동락(Dong-Lak Kim),이형철(H. C. Ri) 한국진공학회(ASCT) 1994 Applied Science and Convergence Technology Vol.3 No.3
가돌리늄 박막의 큐리온도를 자기화의 온도에 따른 변화를 측정함으로써 결정하였다. 박막의 큐리온도는 bulk계의 큐리온도보다 낮아지며 이 박막에서의 큐리온도의 이동은 두께가 얇아질수록 커진다는 것이 관측되었다. 이 실험결과를 유한축적 이론의 관점에서 분석한 결과 전이온도의 이동에 관련된 지수 λ는 0.82±0.13로서 이론적인 값의 1.48과 상치한다는 사실이 발견되었다. 이러한 유한계의 실험치와 유한축척이론과 차이는 여러 유한계에서 관측되었다. We determine the Curie temperature of thin gadolinium films by the measurement of magnetizations as a function of temperature. From this measurement, we observe the systematic shift of Curie temperatures for films, that is, the larger the shift is, the thinner the film is. By analyzing the data in light of finite-size scaling theory, we determine the exponent λ to be 0.82±0.13, not equal to the theoretical prediction of 1.48, which is already seen in other experimental works.
큐리온도 근방에서의 전기적, 자기적 성질변화를 이용한 강자성 가돌리늄의 큐리온도의 결정
이일수(Ilsu Rhee) 한국진공학회(ASCT) 1995 Applied Science and Convergence Technology Vol.4 No.3
자화도와 비저항의 온도에 따른 변화를 측정함으로써 덩치 가돌리늄의 큐리온도를 정확히 결정하였다. 이 두 물리량은 큐리온도에서 비정상적인 특이성을 보여준다. 이들의 특이성에서 결정된 큐리온도의 값은 서로 1度 이내에서 잘 일치함을 보여주었다 The Curie temperature of bulk gadolinium has been accurately determined by measuring the magnetization and the resistivity as a function of temperature. These physical quantities show the anomalous behaviors at Curie temperature. The Curie temperatures determined from these two different physical quantities are found to be consistent with each other within less man one degree.
이일수(Ilsu Rhee) 한국자기학회 1998 韓國磁氣學會誌 Vol.8 No.5
The adiabatic nuclear demagnetization cooling technique has reduced the lowest accessible temperature to the regime of microkelvin, and consequently led to a large expansion in microkelvin physics such as solid and liquid ³He, superconductivity of noble metals, spin glass transition, and nuclear magnetism. Our ability to reach temperature in microkelvin regime has greatly facilitated by the developments of dilution refrigerator and superconductivity magnet. It is appropriate to divide nuclear demagnetization cooling into two categories; those in which only the nuclear spin system is cooled down and those in which the lattice and conduction electrons in the refrigerant or the specimen are also cooled by the cooling power of nuclear spin system. The former cooling technique has utilized to investigate the nuclear magnetism at temperature in nanokelvin regime. The latter is widely used in studying the phenomena occurring in microkelvin regime. In this review paper, we will discuss the basic principles of nuclear demagnetization cooling and its applications. This work is supported by the Basic Science Research Institute Program under Contract number BSRI-97-2404.