Electron and nuclear magnetic relaxation inLa2CuO4and related cuprates

The nuclear-magnetic-resonance spin-lattice relaxation time ($T_1$) and electron-paramagnetic-resonance (EPR) linewidth (${\Gamma }_{\perp }^s$) are calculated for ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$. The large broadening of the EPR at room temperature is shown to narrow with increasing temperature as (ξ/a${)}^3$, where ξ is the two-dimensional spin-correlation length and a is the lattice constant. The NMR $T_1$ at first lengthens with increasing temperature as (ξ/a${)}^{\mathrm{-}1}$, then shortens above T∼J/2, where J is the in-plane exchange coupling. Explicit values are calculated for $T_1$ and ${\Gamma }_{\perp }^2$. .AE