Ferromagnetism and giant magnetoresistance in the rare-earth fullerides Eu6-xSrxC60 -: art. no. 134431

We have studied crystal structure, magnetism, and electric transport properties of a europium fulleride Eu6C60 and its Sr-substituted compounds, Eu6-xSrxC60. They have a bcc structure, which is an isostructure of other M6C60 (M represents an alkali atom or an alkaline-earth atom). Magnetic measurements revealed that magnetic moment is ascribed to the divalent europium atom with S=7/2 spin, and a ferromagnetic transition was observed at T-C=10-14 K. In Eu6C60, we also confirm the ferromagnetic transition by heat-capacity measurement. The striking feature in Eu6-xSrxC60 is very large negative magnetoresistance at low temperature; the resistivity ratio rho(H=9 T)/rho(H=0 T) reaches almost 10(-3) at 1 K in Eu6C60. Such large magnetoresistance is the manifestation of a strong pi-f interaction between conduction carriers on C-60 and 4f electrons of Eu.