Size Dependence Of Structure Research Articles

Size dependence of structure and magnetic properties of CoCr2O4 nanoparticles synthesized by hydrothermal technique

The size dependence of structure and magnetic behavior has been investigated on spinel chromite CoCr2O4 nanoparticles (NPs) with different particles from ~2.8 to ~19.7 nm, synthesized by a hydrothermal technique. The microstructure analysis shows that the lattice parameter increases monotonically with reduced particle sizes. Compared with the bulk sample, all synthesized NPs exhibit lower Curie temperature (TC~87 K) from paramagnetic (PM) to collinear short-range ferrimagnetic (FiM) state, and this PM–FiM transition is gradually degraded with decreased particle sizes and nearly vanishes for ~2.8 nm NPs. No magnetic transition from short-range FiM order to long-range spiral spin structure is found at low temperatures contrast to the bulk ones. Instead, a cluster spin-glass (SG) transition appears for NPs with D≤5.4 nm. The dynamic behavior of the cluster SG can be described by a power law with the spin relaxation time in the range of 10−10–10−8 s and critical exponent zv′=9.9±0.6, in accordance with a three-dimensional Ising SG behavior. The glass transition temperature (Tg) decreases from 16.3 K for ~5.4 nm to 12.8 K for ~2.8 nm NPs.

Glass of monatomic Lennard–Jones system at nanoscale

Structure and stability of glass of monatomic Lennard–Jones (LJ) system at nanoscale compared with those of the bulk counterparts have been studied using the classical molecular dynamics (MD) method. Models have been obtained by cooling from the melts. Structure of the systems was analyzed via radial distribution function (RDF), interatomic distances, the Honeycutt–Andersen analysis and coordination number distributions. Surface and core structures of LJ nanoparticles have been analyzed in details. Density dependence and cooling rate effects on structure of the systems have been found and discussed. In addition, size dependence of structure and properties of nanoparticles has been analyzed in detail. Indeed, we found glass formation in monatomic LJ systems; however, their stability is not high. Evolution of structure and thermodynamics of the systems upon cooling from the melts was found. We also discussed annealing-induced crystallization of LJ glass.

Size Dependence of Structures and Properties of Magnetic Materials

Due to the involvement of high portion of atomic coordination imperfection in surfaces and interfaces, the properties of magnetic nanocrystals dramatically differ from that of the corresponding bulk counterparts, which have led to a surge in both experimental and theoretical investigations in the past decades. This review summarizes the studies for these size-dependent magnetic properties, and additional thermal or phase stabilities, and mechanical properties. To inter- pret the above phenomena, a thermodynamic model for the size dependence and interface dependences of these properties is described, which is based on Lindemann s criterion for melting, Mott s expression for the vibrational melting entropy, and Shi s model for the size-dependent melting temperature. The model without any adjustable parameter is confirmed by a large number of experimental results, and helps us to understand the structures and properties of the magnetic nanocrys- tals. Moreover, other theoretical works on the above properties are also mentioned and commented.

Size Dependence of Structures and Properties of Magnetic Materials

Size Dependence of Structures and Properties of Magnetic Materials

Noble gas nanocrystals in multiporous confinement: Size dependence of structure

High energy electron diffraction experiments performed on neon and argon clusters formed in nanoporous confinement of amorphous carbon films are compared with calculations made for multiply twinned particles such as icosahedra (ico) and decahedra (dec) with a five-fold symmetry as well as face-centered cubic and hexagonal close-packed particles. The analysis was based on the comparison of precise experimental and calculated diffracted intensities with the help of the R (reliability)-factor minimization procedure. We have revealed highly reproducible discrete distribution functions of sizes and applied structures. The comparison with energy calculations made for different structures confirmed that both ico and dec clusters were basically found in the size intervals predicted in the theory. The temperature related effects in the deposition and annealing processes are revealed and discussed.

Size dependence of exciton fine structure in CdSe quantum dots.

We use photoluminescence excitation and fluorescence line narrowing spectroscopies to examine structure observed in the band-edge absorption feature of CdSe quantum dots. We study eight samples ranging from \ensuremath{\sim}15 to \ensuremath{\sim}50 \AA{} in radius to probe the size dependence of this structure. We compare our results with recent theories, which predict band-edge exciton splittings in CdSe dots due to their internal crystal structure, nonspherical shape, and the exchange interaction between the electron and hole. We find reasonable agreement between our data and theory, supporting the observation of exciton fine structure. \textcopyright{} 1996 The American Physical Society.