1. O. V. Klyavin, V. I. Nikolaev, B. I. Smirnov, L. V. Kha- barin, Yu. M. Chernov, and V. V. Shpeizman, Fiz. Tverd. Tela (St. Petersburg) 45(12) 2187 (2003) [Phys. Solid State 45 (12), 2292 (2003)].
2. O. V. Klyavin, V. I. Nikolaev, B. I. Smirnov, L. V. Khabarin, Yu. M. Chernov, and V. V. Shpeizman, Fiz. Tverd. Tela (St. Petersburg) 49(9), 1590 (2007) [Phys. Solid State 49 (9), 1666 (2007)].
3. O. V. Klyavin, V. I. Nikolaev, B. I. Smirnov, L. V. Khabarin, Yu. M. Chernov, and V. V. Shpeizman, Fiz. Tverd. Tela (St. Petersburg) 50(5), 794 (2008) [Phys. Solid State 50 (5), 828 (2003)].
4. O. V. Klyavin, V. I. Nikolaev, B. I. Smirnov, L. V. Khabarin, Yu. M. Chernov, and V. V. Shpeizman, Fiz. Tverd. Tela (St. Petersburg) 50(8), 1402 (2008) [Phys. Solid State 50 (8), 1458 (2008)].
5. O. V. Klyavin, B. A. Mamyrin, L. V. Khabarin, Yu.M. Chernov, V. Z. Bengus, E. D. Tabachnikova, and S. E. Shumilin, Fiz. Tverd. Tela (St. Petersburg) 42(7), 1265 (2000) [Phys. Solid State 42 (7), 1294 (2000)].