1. L.F. Johnson, A.A. Ballman, J. Appl. Phys. 40, 297 (1969)
2. V.G. Dmitriev, E.V. Raevskii, N.M. Rubin et al., Sov. Tech. Phys. Lett. 5, 1440 (1979)
3. L.M. Dorozhkin, I.I. Kuratev, N.I. Leonyuk et al., Sov. Tech. Phys. Lett. 7, 1297 (1981)
4. B.S. Lu, J. Wang, H.F. Pan et al., Chin. Phys. Lett. 3, 413 (1986)
5. Z.D. Luo, A.D. Jiang, Y.C. Huang et al., Chin. Phys. Lett. 6, 440 (1989)