Magnetic properties of TDAE-C60 under pressure

Electron Spin Resonance (ESR) of alpha-TDAE-C-60 in a crystalline form was performed under pressure to investigate the mechanism of ferromagnetic phase transition, where TDAE is tetrakis-dimethylamino-ethylene. Curie temperature T-C decreased parabolically, reaching zero around 9 kbar. It is demonstrated that an antiferro-orbital ordering model of Jahn-Teller distorted C-60(-) anion is consistent with the experimental data, not only qualitatively but also quantitatively. Enough higher pressure than 10 kbar transforms alpha-TDAE-C-60 to beta-type polymerized-form along c-axis with [2+2] cycloadditive mechanism at room temperature. The beta-form is stable even at ambient pressure and up to approximate to430 K. Prominently, in the beta-form, the spin on TDAE(+) cation, Chat was missing in the alpha-form, revives with the ESR g-shift in-between RbC60 polymer and TDAE(+) radical cation.