Jahn-Teller effect and fullerene ferromagnets

The discovery of C-60 and other members of the fullerene family opened new horizons in the design and synthesis of new molecular-based materials. The discovery that TDAE-C-60 exhibits a transition to a ferromagnetic ground state at an unusually high transition temperature T-C = 16 K has been particularly exciting. Intensive work for more than a decade revealed a unique correlation between spin and orientational ordering of Jahn-Teller-distorted C-60(-) ions. In this chapter, we first review the physics of the Jahn-Teller effect in C-60(n-) ions. Then we describe the structural, electronic, and magnetic properties of TDAE-C-60. We also show magnetic resonance data, which provide strong evidence for the correlation between orbital and spin ordering in TDAE-C-60 and allow for the determination of the Jahn-Teller dynamics.