Electron-Nuclear Double Resonance in RbMnF3

Electron-nuclear double resonance in RbMn${\mathrm{F}}_3$ at 4.2°K is reported. Nuclear saturation was detected as a shift in the field required for antiferromagnetic resonance. At $X$-band frequencies, shifts of up to 500 Oe were obtained. The effective nuclear temperature was found to be a function of the nuclear drive frequency, tending asymptotically towards infinity at the unpulled hyperfine frequency of 687.8 MHz. This value is in good agreement with the value obtained from direct NMR. No anomalous splitting of the hyperfine frequency, as observed with direct NMR, was detected. Nuclear saturation has been observed in magnetizing fields both greater and less than the value for spin flop. Transient measurements yielded a value of 50 msec for $T_1$ at 4.2°K.