Magnetic anisotropy of cerium endohedral metallofullerenes

Cerium endohedral metallofullerene (Ce@C-82) is a pi-f composite nanomagnet, where anisotropic f-electron spin is expected to couple with the rotational motion of the fullerene cage that has pi-electron spin. The field cooling effect on the susceptibility of Ce@C-82 in organic solutions suggests that the application of a magnetic field forces the molecular orientations to be aligned, in cooperation with the magnetic anisotropy of the f-electron spin coupled with the molecular orientation. The role of crystal field in the magnetic anisotropy, which is associated with the off-center geometry of the Ce ion in the cage, is clarified by the crystal field analysis. The crystal field effect in the metallofullerene cage is considerably reduced, in contrast to that of ordinary rare-earth compounds. This is consistent with the findings of a small electronic coupling between the f and pi electrons and a shallow potential of the surrounding cage to the Cc ion. As a consequence, the crystal field effect is emphasized in the low-temperature range (below similar to100 K).