1. K. Koike, H. Matsuyama, and K. Hayakawa, Scanning Microsc. 1 (1987) 241.
2. G.G. Hembree, J. Unguris, R.J. Celotta, and D.T. Pierce, Scanning Microsc. 1 (1987) 229.
3. H.P. Oepen and J. Kirschner, Scanning Microsc. 5 (1991) 1.
4. R. Allenspach, J. Magn. Magn. Mater.
129 (1994) 160.
5. G. Chrobok and M. Hofmann, Phys. Lett.
57A (1976) 257.