1. G. A. Prinz, Science 250, 1092 (1990); Phys. Today April (1995), p. 58.
2. S. F. Alvarado, Phys. Rev. Lett. 75, 513 (1995).
3. M. W. J. Prins, R. Jansen, and H. van Kempen, Phys. Rev. B 53, 8105 (1996).
4. R. I. Dzhioev, B. P. Zakharchenya, and V. L. Korenev, Fiz. Tverd. Tela (St. Petersburg) 37, 3510 (1995) [Phys. Solid State 37, 1929 (1995)].
5. R. I. Dzhioev, B. P. Zakharchenya, R. R. Ichkitidze, K. V. Kavokin, and P. E. Pak, Fiz. Tverd. Tela (St. Petersburg) 35, 2821 (1993) [Phys. Solid State 35, 1396 (1993)].