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- 주제어 : Superparamagnetic transition (검색결과 6 건)
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고온열분해법을 이용하여 제조된 산화철 나노입자의 자성특성 연구
이성우(Sung-Woo Lee),정종율(Jong-Ryul Jeong),최규석(Gyu-Seok Choi) 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.2
In this study, iron oxide nanoparticles were synthesized by thermal decomposition method using Fe(acac)₃ and 1- hexadecanol at 330 ℃. TG-DSC is one of the most important characterization techniques to study the Fe₃O₄ nanoparticles generation and growth from reduced mass and endothermal reaction. Analysis of TEM and XRD results yield the average sizes of synthesized spherical magnetite nanoparticles with sizes of 10㎚. We could determine the saturation magnetization and coercivity value using the VSM. ZFC and FC curves measured at 100 Oe with the T<SUB>B</SUB> (blocking temperature) was explained to superparamagnetic transition.
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Superparamagnetic Transition in Ultrasmal Superparamagnetic Iron Oxide Nanoparticles
이일수 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.4
We report the superparamagnetic transition for USPIO (ultrasmall superparamagnetic iron oxide) nanoparticies with an average diameter of 7 nm. This was observed in the zero field cooled/field cooled (ZFC/FC) and hysteresis curves. The field dependence of the blocking temperature followed the Almeida- Thouless linear behavior of a spin glass system below a crossover field of = 300 Oe. However, a more rapid change in the blocking temperature with increasing applied field was observed above , which can be qualitatively explained by the dipole-dipole interactions in the powder sample. The temperature dependence of the coercivity followed a power law of in the intermediate temperature range.
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탄비어 아마드,이일수 한국물리학회 2009 새물리 Vol.58 No.2
A superparamagnetic transition in the contrast agent Feridex was observed in the zero-field cooling/field cooling (ZFC/FC) and hysteresis curves. Using the ZFC curve, we could accurately determine the superparamagnetic transition temperature, which is called the blocking temperature. The blocking temperature of the diluted sample is shifted to a temperature lower than that of the undiluted sample. We could observe this phenomenon with a twelve-times diluted sample. We also observed a nonzero coercivity below the blocking temperature, but the coercivity was zero above the blocking temperature. T2 조영제 Feridex에서 보이는 초상자성 전이를 ZFC/FC (Zero Field Cooling/Field Cooling)곡선과 자기이력곡선을 통해 관찰하였다. 초상자성 전이온도인 blocking온도를 ZFC 곡선에서 결정할 수 있었다. 희석된 시료에서의 초상자성전이온도는 쌍극자-쌍극자 상호작용이 줄어들기 때문에 희석되지 않은 시료의 전이온도보다 낮은 온도로 이동한다. 이를 12배 희석된 시료를 사용하여 확인하였다. Blocking 온도이하인 4.2 K에서 자기 이력곡선을 통해 보자력이 존재함을 알 수 있었고 초상자성 온도이상의 온도인 300 K에서는 보자력이 없어짐을 확인하였다.
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Oleic acid로 코팅된 산화철 (Fe3O4) 나노입자의 초상자성 전이
홍성욱,이일수 한국물리학회 2010 새물리 Vol.60 No.2
We synthesized the iron-oxide (Fe3O4) nanoparticles and coated them with oleic acid. A superparamagnetic transition, as well as hysteresis, was observed in the ZFC/FC nanoparticles. Field The blocking temperature followed a H□ behavior below a crossover field of Hc=300 Oe. However, a slower change in the blocking temperature was observed with increasing applied field above Hc, which can be qualitatively explained by the dipole-dipole interactions in the powder sample. 산화철 (Fe3O4) 나노입자를 공침(coprecipitation)에 의해 형성한 후 그 표면을 oleic acid로 코팅하였다. 코팅된 나노입자는 구형이었고, 전체 직경과 중심 (core) 산화철 입자의 직경은 각각 20 nm, 5 nm로 관찰되었다. 이 나노입자 분말시료에 대해 ZFC/FC (zero filed cooling/field cooling) 곡선을 구하였고, 이를 통해 나노입자들의 강자성에서 초상자성으로의 전이를 관찰할 수 있었다. 그리고 외부자기장에 따른 blocking 온도의 변화를 관찰하였다. Blocking 온도는 외부자기장의 세기가 300 Oe가 될 때까지는 H□의 의존성을 보였으나, 그 이상의 외부자기장에 대해서는 이와 다른 의존성을 보였다. 이는 자성유체에서도 발견된 현상이지만, 분말시료에서는 더 높은 교차자기장 (crossover field)이 관찰되었다. 이는 분말시료에서는 자성유체에서보다 쌍극자-쌍극자상호작용이 크기 때문이다.
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이규원,이철의,A. Gedanken,E. Sominski,Yu. Koltypin 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6
We have studied the magnetic and the electric properties of La_(0.8)Sr_(0.2)MnO_3 (LSMO)nanoparticle-decorated carbon nanotubes (CNTs). The magnetic susceptibility showed a paramagnetic - superparamagnetic phase transition at TSP » 200 K with a blocking temperature of T_B ∼ 120 K, which can be attributed to the LSMO nanoparticles. At T_(SP), the charge transport taking place through the CNTs network showed a metal-insulator transition (MIT) characteristic of the LSMO nanoparticles, indicating a concomitant MIT in the CNTs triggered by the LSMO nanoparticles. In the metallic phase, the charge transport appears to be dominated by a 2D weak localization effect, which at temperatures below T_B was seen to be somewhat suppressed by the internal field. At temperatures below 50 K, a Kondo effect dominates the electric and the magnetic properties.
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Magnetic Property of α-Fe₂O₃ Nanoparticles Prepared by Sonochemistry and Take-off Technique
Y. S. Koo,B. K. Yun,J. H. Jung 한국자기학회 2010 Journal of Magnetics Vol.15 No.1
A new synthetic method for the formation of uniform α-Fe₂O₃ nanoparticles was reported and their magnetic properties were investigated. The sonochemical synthesis and the subsequent take-off technique resulted in spherical shaped α-Fe₂O₃ nanoparticles with an average diameter of 60 ㎚. The temperature- and applied magnetic field-dependent magnetization of the α-Fe₂O₃ nanoparticles was explained by the sum of two contributions, i.e., the Morin transition and superparamagnetism, because the critical size for superparamagnetism was within the size variation of the nanoparticles.
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