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Low-frequency spin dynamics and NMR spin-lattice relaxation in antiferromagnetic rings
Low-frequency spin dynamics and NMR spin-lattice relaxation in antiferromagnetic rings
Itou, T.
7676
Sagane, T.
7677
Oyamada, A.
7678
Maegawa, S.
7679
Igarashi, S.
7680
Yukawa, Y.
7681
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.
journal article
American Physical Society
2011-01
application/pdf
Physical Review B
014404
83
1
5
Physical Review B
AA11187113
10980121
https://niigata-u.repo.nii.ac.jp/record/2262/files/83_014404_1-5.pdf
eng
info:doi/10.1103/PhysRevB.83.014404
Copyright(C)2011 The American Physical Society