NMR Evidence for 1D Antiferromagnetic Properties in C${\mathrm{s}}_1$${\mathrm{C}}_{60}$ and R${\mathrm{b}}_1$${\mathrm{C}}_{60}$ Polymers

We have performed ${}^{13}$C NMR measurements on the three phases of ${\mathrm{A}}_1$ ${\mathrm{C}}_{60}$ $(A=\mathrm{K},\mathrm{Rb},\mathrm{Cs})$ and alkali NMR in C${\mathrm{s}}_1$ ${\mathrm{C}}_{60}$ ${(}^{133}$Cs) and R${\mathrm{b}}_1$ ${\mathrm{C}}_{60}$ ${(}^{87}$Rb). We show that, for R${\mathrm{b}}_1$ ${\mathrm{C}}_{60}$ and C${\mathrm{s}}_1$ ${\mathrm{C}}_{60}$, strong antiferromagnetic (AF) fluctuations persist up to room temperature, suggesting a one-dimensional character. However, ${\mathrm{K}}_1$ ${\mathrm{C}}_{60}$ behaves as an ordinary three-dimensional metal. NMR also reveals a magnetic transition at about 25 K in the Rb and Cs polymers. Comparison of the ${}^{133}$Cs and ${}^{13}$C spectra supports the occurrence of a spin-flop AF phase. Simulations of the ${}^{133}$Cs spectrum due to a distribution of dipolar fields are consistent with moments $m\simeq 0.5{\mu }_B$ ordered in AF chains.