Excitation of Coupled Nuclear Antiferromagnetic Resonance Modes

The presence of a strong hyperfine coupling in the antiferromagnets KMn${\mathrm{F}}_3$ and CsMn${\mathrm{F}}_3$ leads to a strong intermixing of the nuclear magnetic resonance and antiferromagnetic resonance (AFR) modes at low temperatures. In the experiments described here, ${\mathrm{Mn}}^{55}$ resonance absorption is detected by monitoring the field for AFR while driving at appropriate nuclear frequencies. Such resonance absorption is observed for a range of frequencies many times larger than the nuclear linewidth. A spin-pinning model is proposed which provides nucleation centers for this "off-resonance" saturation.