1. a Department of Physical Chemistry , Moscow Institute of Steel and Alloys , Moscow , Leninsky prospekt 4, USSR
2. b Institut für Metallkunde und Metallphysik RWTH Aachen , Kopernikus str. 14, D-5100 , Aachen , Germany
3. d Materials Research Dept , Rensselaer Polytechnic Institute , Troy , NY , 12180-3590 , USA
4. c Department of Solid State Physics , Kossuth Univ. , 4010 Debrecen, P.O. Box 2, Hungary