Nuclear-Resonance Study ofF19in RbMnF3

A nuclear-magnetic-resonance study is made of the ${\mathrm{F}}^{19}$ nucleus in the nearly isotropic antiferromagnet RbMn${\mathrm{F}}_3$ from 1.5 to 300 K. In the paramagnetic region the results are in satisfactory agreement with Moriya's theory applied to this material. In the antiferromagnetic region the spin-lattice relaxation time can be empirically described by an Arrhenius equation over four orders of magnitude. Below 30 K the spin-spin relaxation time is anomalously long-three times that calculated using dipolar interactions alone.