Magnetic moments in Ho3N@C80 and Tb3N@C80

Magnetization M(H,T) measurements on R3N@C80 (R=Ho and Tb) for magnetic fields μ0H up to 5 T and temperatures T down to 1.8 K are presented. For both fullerenes, the M(H,T) curves depend on the ratio H/T only and are well described by Brillouin functions with J=16 and g=1.25 for Ho3N@C80 and J=12, g=1.5 for Tb3N@C80. The corresponding moments per cage of 20 and 18 μB, respectively, cannot be explained by a collinear ferromagnetic or antiferromagnetic alignment of the three R magnetic moments in the encaged cluster (R3N). The observed moments are explained by strong ligand fields acting on the individual, ferromagnetically coupled R moments within the (R3N) cluster.