PHYSICAL REVIEW B, vol. 50, no. 23, page. 17139 - 17142, 1994-12-15
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
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