1. Brugger, T., Schreiner, T., Roth, G., Adelmann, P., Czjzek, G.: (submitted for publication)
2. for reviews see e.g. Grewe, N., Steglich, F.: In: Handbook on the physics and chemistry of rare earths vol. 14. Gschneidner, Jr., K.A., Eyring, L. (eds.) Amsterdam: North-Holland: 1991. See also: Fulde, P., Keller, J., Zwicknagl, G.: In: Solid state physics, vol. 41, p. 1. Ehrenreich, H., Turnbull, D. (eds.). San Diego: Academic Press 1988
3. Adelmann, P., Ahrens, R., Czjzek, G., Roth, G., Schmidt, H., Steinleiter, C.: Phys. Rev. B46, 3619 (1992)
4. Ghamaty, S., Lee, B.W., Markert, J.T., Early, E.A., Bjørnholm, T., Seaman, C.L., Maple, M.B.: Physica C160, 217 (1989)
5. Boothroyd, A.T., Doyle, S.M., Paul, Mc K., Osborn, R.: Phys. Rev. B45, 10075 (1992)