教師著作
Permanent URI for this collectionhttp://rportal.lib.ntnu.edu.tw/handle/20.500.12235/37076
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Item Size-dependent magnetic parameters of fcc FePt nanoparticles: applications to magnetic hyperthermia(IOP Publishing, 2010-04-14) M. S. Seehra; V. Singh; P. Dutta; S. Neeleshwar; Y.-Y. Chen; C.-L. Chen; S.-W. Chou; Chia-Chun ChenFor nominal 3 and 9 nm FePt nanoparticles coated with oleylamine/oleic acid and having a face-centred-cubic (fcc) structure, temperature variations (5–300 K) of magnetization M, ac susceptibility χ' and χ'' for the frequency range fm = 0.1–1000 Hz and electron magnetic resonance (EMR) spectra at 9.28 GHz are reported. X-ray diffraction of the samples shows fcc structure with a lattice constant a = 3.84 Å and TEM characterization yields log-normal distributions of the particle sizes with average D = 3.15(0.16) nm and D = 8.70(0.12) nm for the 3 nm and 9 nm samples, respectively. M versus T data for the zero-field-cooled and field-cooled modes yield a blocking temperature TB = 15 K (85 K) for the 3 nm (9 nm) samples whereas the hysteresis loops at 5 K yield a coercivity Hc = 0 Oe (1.4 kOe). Analysis of the data of TB at different fm determined from the peaks in χ'' in ac susceptibility and the temperature variation of the EMR spectra are used to determine the following parameters of the Vogel–Fulcher relaxation for the 3 nm (9 nm) samples respectively: the attempt frequency fo = 8 × 1010 Hz (2 × 1012 Hz); inter-particle interaction temperature To = 3 K (33 K) and anisotropy Ka = 1.96 × 106 ergs cm−3 (4.3 × 105 ergs cm−3). The use of the above parameters for the calculations of the optimum size for magnetic hyperthermia is analysed and discussed.Item Size-Controlled Ex-nihilo Ferromagnetism in Capped CdSe Quantum Dots(Wiley-VCH Verlag, 2008-05-05) M. S. Seehra; P. Dutta; S. Neeleshwar; Y.-Y. Chen; C.-L. Chen; C.-L. Dong; S.-W. Chou; Chia-Chun Chen; C.-L. ChangHysteresis loops in D = 1.8 nm CdSe-TOPO nanoparticles show ferromagnetism at 5 K and 300 K. Charge transfer from Cd to the Cd–O bond is shown by arrow in the Fourier transforms amplitudes of the EXAFS k2χ data at the Cd K-edge in the smaller 2.8 and 4.1 nm particles. This charge transfer produces holes in the Cd 4d band yielding ferromagnetism varying as 1/D with magnetic moment µ = 0.0075 µB per Cd surface atom.