Magnetic properties of undoped C60

The Heisenberg antiferromagnet, which arises from the large-U Hubbard model, is investigated on the C60 molecule and other fullerenes. The connectivity of C60 leads to an exotic classical ground state with nontrivial topology. We argue that there is no phase transition in the Hubbard model as a function of U/t, and thus the large-U solution is relevant for the physical case of intermediate coupling. The system undergoes a first-order metamagnetic phase transition. We also consider the S=1/2 case using perturbation theory. Experimental tests are suggested.