Volume 96, Issue 2, 15 July 2004
Index of content:
96(2004); http://dx.doi.org/10.1063/1.1762993View Description Hide Description
Nonresonant Raman scatteringmeasurements were performed on a three-layered sample of in situannealed InAs/GaAs self-assembledquantum dots. The thermal annealing step was done during the growth of each GaAs spacer layer, where the substrate temperature was raised from 530 °C to 580 °C as measured by a pyrometer. Three Raman signals are clearly seen at 264 268 and 271.5 which can be attributed to the longitudinal optic (LO) phonons of the dots. These three different signals are attributed to different degrees of In/Ga alloying or intermixing in each dot layer as a consequence of the different thermal treatments that each layer was subjected to. The Raman signal of the wetting layer (WL) is remarkably weak and suggests erosion of the wetting layer. In contrast, Raman scatteringmeasurements on an unannealed sample show two overlapping features at 259.5 and 261.5 which are attributed to the LO phonons of the dots. The WL signal is clearly observed at 251.5 To support our Raman observations, the appearance of a strong higher-energy peak in photoluminescence measurements suggests that alloying did occur in the annealed sample.
96(2004); http://dx.doi.org/10.1063/1.1760831View Description Hide Description
The phase relaxation time of biexcitons and that of excitons in a bulk ZnO have been measured by the use of femtosecond four-wave mixing as functions of excitation wavelength, excitation power, and temperature. The biexciton-acoustic phonon interaction coefficient has been determined to be as an average value. For A excitons, the interaction coefficients with acoustic and optical phonons have been determined to be and respectively.
96(2004); http://dx.doi.org/10.1063/1.1762707View Description Hide Description
Spinel-type ferrites are widely used in practical applications. A fascinating property of Zn-Ni ferrites which reveals a direction for application is reported. A large negative magnetoresistanceeffect has been observed in and Ni substituted ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature and a spin (cluster) glass transition was found for some compositions at low temperatures. The magnetoresistance is either parabolic or linear with respect to applied field up to 9 T depending on the compositions and temperatures. It was found that the magnetoresistanceeffect increases as the Ni content increases in up to and then again decreases and finally become negligible for i.e., This magnetoresistanceeffect can be explained with the help of spin-dependent scattering and the Yafet-Kittel angle of the Ni-substituted Zn-Ni ferrites.
96(2004); http://dx.doi.org/10.1063/1.1760834View Description Hide Description
Exchange-coupled or Pr) nanocomposite bulk magnets with nearly full density have been successfully produced by shock compaction of melt-spun powders.X-ray diffraction and transmission electronic microscopy analyses of the shock-consolidated compacts showed no grain growth upon compaction, in fact, a decrease in the crystallite size of both the hard and soft phases was observed. As a consequence, magnetic properties were retained and even improved after compaction. Hysteresis loops of the shock-consolidated powder compacts showed a smooth single-phaselike behavior, indicating effective exchange coupling between hard and soft magnetic phases.