Sy Hong Kok

Real space renormalization of Ising models

Sy Hong Kok

Magnetism plays a central role in the technology of information storage and retrieval. Magnetic materials of high coecivity form the basic structure of magnetic disks for computer systems and magnetic tape for tape recordings. In collaboration with the Centre for Superconductivity and Magnetic Materials, we study properties of magnetic materials and doped ferromagnetic compounds using the state of the art first principles electronic structure calculation. Vacancy, antisite defect concentra-tions and their formation energies as a function of bulk composition and temperature for undoped compounds are also studied using a combined statistical mechanical approach with first-principles calculations. Modelling and simulation are carried out to study the magnetic hysteresis, reversal processes, and domain patterns in hard magnetic materials utilised as thin-film recording media. (Tsing Hua University, China).

Various computational techniques are used to study materials of both scientific and engineering interests. Current projects include dislocations in metals, defects in semiconductors, semiconductor and metallic surfaces, semiconductor clusters, as well as bio-macromolecules. We use a wide range of computational methods including classical molecular dynamics, tight-binding molecular dynamics, embedded atom method, and the state of the art first principles electronic structure calculation.

With the advance of crystal growth techniques such as molecular beam epitaxy, it has become possible to grow high quality low-dimensional quantum structures, such as superlattices, quantum wells, quantum wires and quantum dots. These structures have become of great interest because of their enhanced mobilities when they are doped and the appearance of strong exciton peaks which persist even at room temperature. Our research effort is to understand the effect of the quantum confinement on the exciton and to study optical properties in such low-dimensional quantum structures by performing theoretical calculations based on simple models. (^‡Department of Physics, Illinois Institute of Technology).

Sy H K and F Chen, Curie temperatures for a two-component Ising ferromagnetic superlattice, Solid State Comm. 105, 189-193 (1998).

Zhao G P, Ong C K, Feng Y P, Lim H S, and Ding J, Remanence enhancement of single-phased isotropic nanostructured permanent magnets, Journal of Magnetism and Magneteic Materials, 192, 543-552 (1999).

Zhao G P, Lim H S, Ong C. K, and Y. P. Feng, Remanence enhancement in nano-structured composite magnets, Journal of Physics: Condensed Matter, 11, 3323-3334 (1999).

Feng Y P, Ong C K, Poon H C, and Tomanek D, Tight-binding molecular dynamics simulations of semiconductor alloys: Clusters, Surfaces and Defects, Journal of Physics: Condensed Matter, 9, 4345-4364, (1997).

Koh T S, Feng Y P, and Spector H N, Elastic scattering of excitons by excitons in semiconducting quantum well structures: Finite confining potential model, Phys. Rev. B, 55, 9271 (1997).