Proton spin-lattice relaxation in TMMC [(CH3)4NMnCl3]

Abstract

We examine the temperature and frequency dependence of the proton spin-lattice relaxation rate $\frac{1}{T_1}$, as a probe of the electron-spin dynamics of the quasi-one-dimensional exchange-coupled paramagnet TMMC [${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$ NMn${\mathrm{Cl}}_3$]. The rate is measured from 5.5-16 MHz and from 1.4 °K to room temperature. An extension of Moriya's magnetic-relaxation theory to the linear-chain system, using the exact classical results for static spin-correlation functions, gives over-all good quantitative agreement between theory and experiment. A sharp minimum in $\frac{1}{T_1}$ at $T\simeq 18$ °K, an ${\omega }^{-\frac{1}{2}}$ dependence on frequency at room temperature and ${\omega }^{-\frac{3}{2}}$ at low temperature, with the external field parallel to the chain, and the frequency independence of $\frac{1}{T_1}$ at room temperature with the field perpendicular to the chain are all explained by the theory.