Strong ferromagnetic exchange among mixed valent Ce in CeMn6Al6

X-ray, resistivity, magnetization and Moessbauer studies of dilute probes of Fe57 and Gd155 in CeMn6Al6 were performed. All studies indicate that Ce in CeMn6Al6 is in a mixed valent state. The magnetization studies show that the Ce contribution to the susceptibility is very small at low temperatures, increases to a huge maximum at 100 K (approx. 3x10-2emu/mole) and follows Curie Weiss law at high temperatures. The experimental observations are interpreted in terms of interconfigurational fluctuations between Ce4+ (ground state) and Ce3+ ions. The detailed analysis, which considers also coupling with the Mn sublattice, yields for the Ce interconfigurational excitation energy, the value of 223 K and for the Ce-Ce exchange coupling 47 K. (Auth.)