Simultaneous Fermion and Boson Spin Dynamics in a One-Dimensional Antiferromagnet

The proton NMR spin-lattice relaxation time $T_1$ has been measured in the spin-½ one-dimensional antiferromagnet (1DAF) $\alpha$-bis (N-methylsalicylaldiminato)-copper (II) (CuNSal) at low temperatures and high fields. $T_1$ is dominated by electron spin fluctuations of the 1DAF, and we show that these fluctuations are described by Fermi-Dirac statistics for the one-magnon contribution to $T_1$ but that the two-magnon part is given by Bose-Einstein statistics.