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Synthesis of colloidal Mn2+: ZnO quantum dots and high-Tc ferromagnetic nanocrystalline thin films
被引:394
作者:
Norberg, NS
Kittilstved, KR
Amonette, JE
Kukkadapu, RK
Schwartz, DA
Gamelin, DR
[1
]
机构:
[1] Univ Washington, Dept Chem, Seattle, WA 98195 USA
[2] Pacific NW Natl Lab, Richland, WA 99352 USA
关键词:
D O I:
10.1021/ja048427j
中图分类号:
O6 [化学];
学科分类号:
0703 ;
摘要:
We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)(2) was found to strongly inhibit oxidation of Mn2+ by O-2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+ :ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+ :ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 mu(B)/Mn2+ and T-C > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.
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页码:9387 / 9398
页数:12
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