Harnessing Complexity: Magnetic/Magnetoresistive/Magnetocaloric Materials (Intermetallics and Chalcogenides) Electrons in metallic materials are responsible to both electrical conduction and ferromagnetism (metallic magnetism). Metallic magnets have been around us for many centuries but have become more significant in recent years in terms of their multifunctional properties such as magnetoresistivity and magnetocaloric effect. However, the design of such multifunctional metals requires further understanding of underpinning chemistry and physics of the metallic magnets, as chemical principles of structure formation are intrinsically coupled to the physical properties of metals. In this area of research, our interests include giant magnetoresistive intermetallics, giant/colossal magnetocaloric materials, spin frustration of localized magnetic moments in metals, theoretical prediction of magnetic exchange interactions in metals. Theoretical Understanding of Metallic Magnetism and Metallic Bonding for Property Design We are currently developing a unified theory of magnetic exchange interactions in different classes of magnetic materials from molecules to semiconductors/insulators to metals. The theory is based on a perturbational treatment of spin polarization in materials within density functional formalism. The method has identified phase relationships of wavefunctions near the Fermi level as the critical component in determining spin polarization patterns in metals. The phase relationship can be monitored in direct space through the concept of relative entropy density which we have utilized for chemical bonding analysis. NanoMaterials (Functionalized Quantum Dots and Their Composites) CdSe and related colloidal quantum dots are potentially important optical materials in the future, and not surprisingly, there are currently more than 300 US patents related to the quantum dots. One current bottleneck of the future applications of the quantum dots is a lack of suitable methods that can functionalize the surface of the quantum dots as we desire. We propose to solve the problem by utilizing our newly-developed synthetic method for the quantum dots and thus to provide multifunctionalities in quantum-dot composites in various forms. Active Porous Materials and Hybrids Nanoporous structures provide additional functionalities to materials when the pores are accessible by other chemicals and thus highly porous materials are of interest for use in catalysis, separations, gas storage, sensors, and other applications. The porous materials also can be utilized as a nanoreactor in which the wall-surface properties are tailored to influence the chemical reactions in nanoscale. We are currently interested in developing general large-scale preparative routes for porous structures for oxides including alumina, zirconia and conducting oxides. In addition to possible interesting chemistry in the nanopores, these materials have applications in batteries, solar-cell fabrications, hydrogen storage and others. Current Research Interests
porous conducting oxide
TaS3 nanofibers (TEM)
nano-to-nano
TaS3 nanofibers (SEM)
MoS2 nanodisks
PrMnSi2
GMR of PrMnSi2
strong magnetic hysteresis of PrMnSi2
SP-POT
perturbations by spin polarization
atomic exchange parameters
spin polarization in TM complexes
Stoner condition for ferromagnetism
non-rigid band behavior of NiMnSb
chemical bonding vs. spin polarization
p-metal-rich ferromagnetic Mn2Ga5
spin polarization in Mn2Ga5
2D superdegeneracy in Mn2Ga5
origin of 2D super-degeneracy in Mn2Ga5
microwave reactor for QD syntheses
colloidal CdSe and ZnS:Mn QDs
largest photoluminescent CdSe QDs reported
new scaling law of quantum confinement CdS
one-pot functionalization of CdSe@Zns QDs
silica monoliths with embedded QDs
surface functionalization
QD-polystyrene composites