Mott transition with antiferromagnetic ordering in ammoniated alkali C-60 superconductors: NMR studies

C-13-NMR measurements were performed for ammoniated A(3)C(60) (A = alkali m etals) superconductors. (NH3)(x)A(3)C(60) For (NH3)K3C60 the Curie-Weiss-ty pe T dependence of susceptibility and T-independent nuclear relaxation rate . 1/ T-1 = const.. were observed at high Ts above 150 K, indicating the loc alized spin stare of C-60 molecular spins. The extremely broadened spectra for C-13-NMR was observed below T-N similar to 45 K. providing unambiguous evidence for an antiferromagnetic order with a moment of mu(0) similar to 1 mu(B)/C-60. The present NMR measurements clearly showed that the intercala tion of NH3 makes (NH3)K3C60 a Mott-Hubbard insulator with AF order below T -N similar to 45 K. We also discuss the partially ammoniated A(3)C(60). (C) 2000 Elsevier Science B.V. All rights reserved.