PHYSICAL REVIEW B, vol. 51, no. 24, page. 17635 - 17641, 1995-06-15
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, vol. 27, no. 5, page. 544 - 549, 1994-10
PHYSICAL REVIEW B, vol. 49, no. 14, page. 9555 - 9559, 1994-04-01
PHYSICAL REVIEW B, vol. 47, no. 6, page. 2979 - 2982, 1993-02-01