Affiliation: | (1) Department of Experimental Physics, Comenius University, Mlynska dolina F-2, 84215 Bratislava, Czechoslovakia;(2) Present address: Institute of Physics, EPRC SAS, Dúbravská cesta 9, 842 28 Bratislava, Czechoslovakia;(3) Present address: Polytechnical University of Kim Cak, Pyong-yang, Democratic Public Republik of Korea;(4) Present address: Department of Physical Electronics, Purkynie University, Kotláská 2, 611 37 Brno, Czechoslovakia |