Magnetic ion-doped semiconductor nanocrystals (NCs) have recently drawn a great deal of interest because of the intriguing physical properties and the application potential in spintronics and magneto-electronics. In this work, we report on theoretical studies of magnetism in colloidal CdSe NCs doped with Mn2+ ions. Numerically, the exact diagonalization (ED) technique is employed to calculate the electronic structures and magnetizations of singly changed CdSe NCs doped with four Mn ions in various spatial distributions. The numerical results show that the magnetism in a few-Mn doped NC is not only determined by the total number of Mn ions, but also sensitively depends on the individual locations, which are however hardly considered by widely used mean field theory. Remarkably, the formation of Mn clusters in a NC leads to the significant deviation of the magnetization from the standard Brillouin function description for an ideal paramagnet. The quantum size effect is shown to enhance the magnetizations of magnetic NCs via the interactions between the quantum confined carriers and Mn-clusters. A solvable constant interaction model (CIM) with the consideration of individual Mn spins is presented for the explanation of the numerical data.
The addition of Al increases the temperature and activation energy of crystallization of the fast-growth type Sb70Te30
recording film so that the archival stability will be improved. Meanwhile, the addition of Al increases the temperature
and activation energy of melting of the Sb70Te30 recording film so that the local melting of the crystalline Sb and Sb2Te3
phases will be suppressed. The pulsed laser powers required to trigger crystallization, melting, and ablation of Sb70Te30
recording film increase with increasing Al content indicating the increased stability of the non-crystalline phase, in the
meantime, the increased melting and ablation powers indicating the Al addition could increase the melting temperature
and prevent ablation effect of the Sb70Te30 recording film.
The effects of the film thickness and foreign element addition on the crystallization kinetics and optical properties of eutectic Sb70Te30 phase change recording film have been studied. The crystallization temperature and activation energy for crystallization of the non-doped Sb70Te30 recording films were decreased from 161 to 145, 144, 141, and 125°C, and from 3.0 to 2.6, 2.3, 2.0, and 1.9 eV/atom, respectively, when the thickness was increased from 15 to 20, 25, 30 and 100 nm. For the Ag-doped Sb70Te30 recording film of 20 nm in thickness, the crystallization temperature was found to increase from 145 to 146 and 156°C, and the activation energy was found to decrease from 2.6 to 2.5 and 2.1 eV/atom, respectively, as the concentration of Ag was increased from 0 to 3.8 and 11.8 at%, respectively. Meanwhile, the crystallization temperature and activation energy of the 20-nm-thick In-doped Sb70Te30 film was found to increase from 145 to 153 and 168°C, and increased from 2.6 to 2.8 and 3.4 eV/atom, respectively, as the concentration of In was increased from 0 to 1.4 and 4.8 at%.
New Ga doped GeSb based phase-change materials are investigated. These materials possess good optical contrast at short wavelengths. Crystallization temperature increasing and grain size refinement are obtained by addition of Ga. More than 50 dB CNR and 25 dB erasability are measured in disks using blue laser.