Ferromagnetism and giant magnetoresistance in the rare-earth fullerides (formula presented)

We have studied crystal structure, magnetism, and electric transport properties of a europium fulleride (formula presented) and its Sr-substituted compounds, (formula presented) They have a bcc structure, which is an isostructure of other (formula presented) (formula presented) represents an alkali atom or an alkaline-earth atom). Magnetic measurements revealed that magnetic moment is ascribed to the divalent europium atom with (formula presented) spin, and a ferromagnetic transition was observed at (formula presented) In (formula presented) we also confirm the ferromagnetic transition by heat-capacity measurement. The striking feature in (formula presented) is very large negative magnetoresistance at low temperature; the resistivity ratio (formula presented) reaches almost (formula presented) at 1 K in (formula presented) Such large magnetoresistance is the manifestation of a strong (formula presented) interaction between conduction carriers on (formula presented) and (formula presented)(formula presented) electrons of Eu.