Browsing by Author "Jian, WB"

Now showing 1 - 4 of 4

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.
Electron-phonon scattering times in crystalline disordered titanium alloys between 3 and 15 K
(1998-05-01)
Wu, CY
;
Jian, WB
;
Lin, JJ
;
物理研究所
;
Institute of Physics
We have successfully fabricated bulk crystalline disordered titanium alloys (Ti1-xSnx, T1-xGex, and Ti0.97-xSn0.03Scx) with nominal concentration x of the order of a few at. %. The impurity atoms are gradually introduced into a titanium host to tune the degree of disorder, resulting in residual resistivities rho(0) varying from approximate to 40 to 160 mu Omega cm (corresponding to values of k(F)l approximate to 5-20, with k(F) being the Fermi wave number and l being the electron elastic mean free path). With this wide range of experimentally accessible rho(0), we are able to perform systematic studies of the disorder rho(0), or electron elastic mean free path l, behavior of the electron-phonon scattering time tau(ph). We have measured the magnetoresistivities of these alloys between 3 and 15 K, and compared our results with weak-localization theoretical predictions to extract tau(ph)(T,l) Unexpectedly, we obtain a rather diversified temperature dependence and disorder dependence of tau(ph) as follows. (a) In Ti1-xSnx alloys with rho(0) greater than or similar to 100 mu Omega cm we find 1/tau(ph)similar to T-2/l. (b) In Ti1-xSnx alloys with rho(0) less than or similar to 70 mu Omega cm we find 1/tau(ph)similar to T-3/l. (c) In Ti1-xGex alloys with 50 less than or similar to p(0) less than or similar to 130 mu Omega cm we find 1/tau(ph)similar to T-3 in some alloys and 1/tau(ph)similar to T-4 in others, while at a given temperature 1/tau(ph) is essentially independent of disorder. (d) In Ti0.97-xSn0.03Scx alloys with 55 less than or similar to rho(0) less than or similar to 75 mu Omega cm we obtain 1/tau(ph)similar to T-2. These experimental observations altogether imply that electron-phonon interactions in the presence of strong impurity scattering are very sensitive to the local material environment (the microscopic quality) of a particular sample system, which might be variously modulated with the doping of different kinds of impurity atoms. Our results are compared with existing theoretical predictions for electron-phonon scattering in disordered conductors.
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.