SPring-8, the large synchrotron radiation facility

Date & Time: 17:00-, October 17, 2005

Speaker: Prof. Takafumi Miyanaga
Affiliation: Faculty of Science and Technology, Hirosaki University

Abstract
This talk will be given in Japanese.

　　X-ray absorption fine structure (XAFS) is developed with a growth of synchrotron radiation source. XAFS is expanded in many fields but its limitation has been also appeared. XAFS has two characteristic features : X-ray absorption spectroscopy and structural analyses by photoelectron interference.
　　In this seminar, I will show that our recent works for the application of XAFS to (1) ferroelectrics, (2) semiconductors and (3) magnetic materials.
(1) Some ferroelectric materials show displacive and order-disorder structural phase transitions. By combining between XAFS and other techniques their relations were revealed. XAFS shows the local structural change and their Debye-Waller factor is diverged at Tc, which is typical behavior in the phase transition.
(2) It is pointed out that although single-quantum-well (SQW) of InGaN (this is blue-color LED) has high density of threading dislocations, it shows a high quantum efficiency. In K-edge XAFS shows that there is correlation between a mole fluctuation of In atoms and the external quantum efficiency of InGaN SQW.
(3) Ni-Mn magnetic alloys show order-disorder transitions and their magnetic properties change drastically by the order of Mn atoms. Recent GMR study revealed that ferromagnetic nano-cluster plays an important role in the magnetism in the alloys. Magnetic XAFS is powerful technique for the study of local magnetic structures in the clusters.
Experimental results obtained at SPring-8 and theoretical calculations are presented.