1. Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353, Korea
2. FRM II, Technische Universität München, Lichtenbergstrasse 1, D-85747 Garching, Germany
3. Institut für Kristallographie, RWTH Aachen, Jägerstrasse 17-19, D-52056 Aachen, Germany
4. Department of Nano Systems Engineering, Center for Nano Manufacturing, Inje University, Gimhae, Gyeongnam 621-749, Korea