@article{oai:niigata-u.repo.nii.ac.jp:00002262,
 author = {Itou, T. and Sagane, T. and Oyamada, A. and Maegawa, S. and Igarashi, S. and Yukawa, Y.},
 issue = {014404},
 journal = {Physical Review B, Physical Review B},
 month = {Jan},
 note = {We develop a general theory of the spin dynamics of Heisenberg antiferromagnetic rings (HAFRs) that explains the mechanism of NMR spin-lattice relaxation at low temperatures. In HAFRs, the imaginary parts of the q-summed dynamic spin susceptibilities parallel and perpendicular to an applied static field, χ′′sum∥(ω) and χ′′sum⊥(ω), are composed of the sum of many slightly broadened δ-functional modes at many frequencies. The NMR relaxation is caused by the quasielastic mode in χ′′sum∥(ω) at around zero frequency. This quasielastic mode is characterized by two physical quantities, intensity P0∥ and frequency width Γ0∥. Although P0∥ has to date been assumed to be identical to the uniform static susceptibility, we point out that the two quantities are not identical. Without making this unreliable assumption for P0∥, we demonstrate experimentally how P0∥ and Γ0∥ behave, by analyzing the NMR relaxation rates of two different nuclei, H1 and C13, in a real HAFR. This analysis is more rigorous and thus can be used to estimate Γ0∥ and P0∥ more precisely than previously possible. We find that the temperature dependence of P0∥ exhibits activation-type behavior reflecting the first excitation gap. We also find that Γ0∥ decreases monotonically on cooling but saturates to a nonzero value at zero temperature. This strongly suggests that Γ0∥ is dominated not only by the electron-phonon interactions but also by internanomagnet dipole interactions, which have been neglected to date.},
 pages = {1--5},
 title = {Low-frequency spin dynamics and NMR spin-lattice relaxation in antiferromagnetic rings},
 volume = {83},
 year = {2011}
}