1. M. Pacheco, Z. Barticevic, F. Claro, J. Phys.: Condens. Matter 5, A363 (1993); Z. Barticevic, M. Pacheco, F. Claro, Phys. Rev. B 51, 14414 (1995); M. Pacheco, Z. Barticevic, Phys. Rev. B 64, 033406 (2001)
2. K.L. Janssens, F.M. Peeters, V.A. Schweigert, Phys. Rev. B 63, 205311 (2001)
3. Z. Barticevic, M. Pacheco, C.A. Duque, L.E. Oliveira, J. Phys.: Condens. Matter 14, 1021 (2002)
4. I.E. Itskevich, S.G. Lyapin, I.A. Troyan, P.C. Klipstein, L. Eaves, P.C. Main, M. Henini, Phys. Rev. B 58, R4250 (1998); I.E. Itskevich, M.S. Skolnick, D.J. Mowbray, I.A. Troyan, S.G. Lyapin, L.R. Wilson, M.J. Steer, M. Hopkinson, L. Eaves, P.C. Main, Phys. Rev. B 60, R2185 (1999)
5. B.S. Ma, X.D. Wang, F.H. Su, Z.L. Fang, K. Ding, Z.C. Niu, G.H. Li, J. Appl. Phys. 95, 933 (2004)