Nuclear relaxation ofF19in the two-dimensional ferromagnetK2CuF4

Abstract

The spin-lattice and transverse relaxation times ${T}_{1}$ and ${T}_{2}$ of $^{19}\mathrm{F}$ nuclei at different sites were measured, between 1.65 and 4.3\ifmmode^\circ\else\textdegree\fi{}K, in a single crystal of ${\mathrm{K}}_{2}$Cu${\mathrm{F}}_{4}$ with a dc magnetic field ${H}_{0}$ applied along one of the principal axes of the hyperfine-interaction tensor. The field and temperature dependence of ${T}_{1}$ is close to that of the three-magnon process calculated for an anisotropic hyperfine interaction, in a two-dimensional Heisenberg ferromagnet. At 4.3\ifmmode^\circ\else\textdegree\fi{}K, the contributions to the nuclear transverse relaxation are shown to arise chiefly from the two-magnon process for the site with ${H}_{0}$ parallel to the bond axis and from the Suhl-Nakamura interaction for the site with ${H}_{0}$ perpendicular to it, as a consequence of the highly anisotropic hyperfine interaction.