Results of proton spin-lattice relaxation time ($T_{1n}$) measurements on ${\mathrm{C}\mathrm{u}\left(\mathrm{N}{\mathrm{O}}_3\right)}_2$·2½${\mathrm{H}}_2$O at $T=4.2\mathrm{}$ K for $5 \mathrm{kOe}<H<\mathrm{}60\mathrm{} \mathrm{kOe}$ are presented. The data are related to the spin fluctuations in the anisotropic (${J_E}^{\perp }=2\mathrm{}{J_E}^{\parallel }$) antiferromagnetic chains of effective spins $S^{\prime }=\frac{1}{2}$. The results compare favorably with the theoretical results of McFadden and Tahir-Kheli over the whole frequency range up to $8{\omega }_x$ $({\omega }_x=\frac{\left|{J_E}^{\perp }\right|}{\hslash })$.

• Received 31 July 1978

DOI:https://doi.org/10.1103/PhysRevLett.41.1520