Mn55Nuclear Magnetic Resonance in MnF2—The Suhl-Nakamura Interaction

The NMR of ${\mathrm{Mn}}^{55}$ in antiferromagnetic Mn${\mathrm{F}}_2$ has been reexamined, using both superregenerative and pulsed NMR techniques, in the temperature region 1.3-20°K. Instead of the single resonance originally reported, five distinct quadrupolar-split transitions are observed, whose separation yields a value of $\frac{e^2\mathrm{qQ}}{\hslash }=11.7\mathrm{}\pm 0.3$ MHz. The frequency of the central (½ ↔ -½) transition extrapolates to 670.38±0.05 MHz at 0°K. Were there no changes in the hyperfine interaction in going from Zn${\mathrm{F}}_2$: Mn to Mn${\mathrm{F}}_2$, this would imply $\frac{{〈S_z〉}_0}{S}=(99.41\mathrm{}\pm 0.03)\%$ in the antiferromagnetic ground state. The magnitude and $m$ dependence of the linewidths of the individual transitions are reasonably consistent with the predictions of the Suhl-Nakamura theory (i.e., the indirect nuclear spin-spin interaction via virtual spin-wave excitations). The failure to observe a transient signal is attributed to the very short $T_2(<\mathrm{}1\mathrm{} \mu sec)$ resulting from the latter interaction.