F-19 SPIN-LATTICE RELAXATION IN ANTI-FERROMAGNETS WITH THE PEROVSKITE STRUCTURE

The results of the 19F spin-lattice relaxation rate measurements in single crystal KNiF3 as a function of temperature are reported. In the temperature range TN≳T≳0.05 TN (T N=246 K) two clearly different relaxation mechanisms are effective. At low temperatures (T<26 K) the relaxation rate 1/T1 increases slowly with temperature. At higher temperatures the variation with temperature is much faster. The data as a function of a reduced temperature show a striking similarity with previous results for another simple perovskite antiferromagnet, RbMnF3, suggesting that in both temperature ranges the relaxation is due to intrinsic processes. Various possible relaxation mechanisms are discussed.