Observation of Mössbauer resonance line splitting caused by Rabi oscillations

We present the first experimental observation of the Rabi splitting of Mössbauer resonance lines. A radio-frequency magnetic field is tuned to induce transitions between hyperfine sublevels of the Zeeman-split excited or ground state of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei. The line splitting corresponding to the Rabi flopping frequency is observed using a magnetically soft ${}_{}{}^{57}{}_{}{}^{}\mathrm{FeNi}$ absorber foil of composition with almost zero magnetostriction.