1. Fischer, K.H., Hertz, J.A.: Cambridge studies in magnetism, 1. New York: Cambridge University Press 1991; Chowdhury, D.: Spin glasses and other frustrated systems. Singapore: World Scientific 1986; Maletta, H., Zinn, W.: In: Handbook on the physics and chemistry of rare earths, vol. 12. Amsterdam: North-Holland 1986
2. Binder, K., Young, A.P.: Rev. Mod. Phys.58, 801 (1986)
3. Walstedt, R.E., Walker, L.R.: J. Appl. Phys.53, 7985 (1982)
4. Walker, L.R., Walstedt, R.E.: J. Magn. Magn. Mater.31?34, 1289 (1983)
5. Tempelmann, C., Br�mer, H.: Z. Phys. B-Condensed Matter62, 463 (1986)