Experimental study of high-temperature spin dynamics in one-dimensional Heisenberg paramagnets

Abstract

From room-temperature measurements of proton spin-lattice relaxation rate in (${\mathrm{C}{\mathrm{H}}_3)}_4$NMn${\mathrm{Cl}}_3$ (TMMC) and CsMn${\mathrm{Cl}}_3$ · 2${\mathrm{H}}_2$O (CMC) as a function of magnetic field $\overrightarrow{\mathrm{H}}$ the shape of the low-frequency spectral density of the spin fluctuations is directly obtained. For $\overrightarrow{\mathrm{H}}$ parallel to the chain axis the spectral density contains a diffusive term which diverges as ${\omega }^{-\frac{1}{2}}$. The experimental results for $\overrightarrow{\mathrm{H}}\parallel \overrightarrow{\mathrm{c}}$ are in good agreement with a theoretical calculation in TMMC in which the two-spin correlation function is assumed to decay at long times as $t^{-\frac{1}{2}}$. The lack of frequency dependence of $\overrightarrow{\mathrm{H}}$ perpendicular to the chain axis indicates a difference in the "cutoff" time of the two-spin correlation function for the spin components parallel and perpendicular with respect to the external magnetic field.