Browsing by Author "Lan, MD"

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Direct observation of structure effect on ferromagnetism in Zn1-xCoxO nanowires
(2006-06-01)
Jian, WB
;
Wu, ZY
;
Huang, RT
;
Chen, FR
;
Kai, JJ
Diameter-controllable single-crystalline ZnO nanowires (NWs), with the [0001] growth direction in the plane, have been fabricated by using thermal evaporation method. The as-grown NWs with diameters of similar to 40 nm were implanted with various amounts of Co ions. These Zn1-xCoxO (x <= 0.11) NWs possessed a high density of bombardment-induced orientation variations and stacking faults, and exhibited paramagnetic behavior. After thermal annealing, the structural defects largely disappeared and noticeable hysteresis in the magnetization loops were observed, indicating the presence of apparent ferromagnetic ordering in the NWs. This result provides important insight into the role played by defects in relation to the occurrence of ferromagnetism in diluted magnetic semiconductor NWs.
Orbital susceptibilities of PbSe quantum dots
(2006-02-14)
Jian, WB
;
Lu, WG
;
Fang, JY
;
Chiang, SJ
;
Lan, MD
Different sizes of three-dimensional PbSe quantum dots have been synthesized for the study of orbital magnetic susceptibilities. Two types of orbital susceptibilities have been found, including the Curie susceptibility and finite-size corrections to the Landau susceptibility. The Curie term of a quantum dot manifests itself in the temperature dependence of magnetic susceptibility at low temperatures, while the field dependence of differential susceptibility at high temperatures shows finite-size corrections to the Landau susceptibility. Both of the two kinds of orbital susceptibility, estimated per quantum dot, show linear dependence on the size. (c) 2006 American Institute of Physics.
Spontaneous magnetization and ferromagnetism in PbSe quantum dots
(2006-04-15)
Jian, WB
;
Lu, WG
;
Fang, J
;
Lan, MD
;
Lin, JJ
A high-temperature organic solution approach was applied to prepare crystalline PbSe quantum dots. It is diamagnetic with an atomic susceptibility of similar to-1.0x10(-4) emu/mol Oe for bulk PbSe. The core diamagnetism of bulk PbSe was subtracted from our raw data. While transforming into the nanophase, orbital susceptibility including finite-size corrections to the Landau susceptibility has been observed. A paramagnetic zero-field peak with a large diamagnetic susceptibility in high fields exhibit in the field dependent susceptibility as characteristics of the Landau orbital susceptibility. At low temperatures and fields the paramagnetism dominates the contribution of magnetization of quantum dots while the diamagnetism dominates at high temperatures and fields. All these measurements, showing paramagnetism at low fields, indicate the existence of spontaneous magnetization in the quantum dot. In addition, we have observed profound hysteresis loops implying ferromagnetism among the quantum dots even at room temperature, which is spontaneous magnetization in the quantum dot and of the ferromagnetic order among these quantum dots. (C) 2006 American Institute of Physics.