Non-linear spin lattice dynamic in KR(MoO4)2

We report on an investigation of electron paramagnetic resonance spectra in binary molibdates KR(MoO₄)₂ (R³⁺ is the a rare-earth ion). The experiments partly were performed using high magnetic fields laboratory (HFML) and the terahertz free electron laser (FLARE) at Radboud University. This unique combination allows us to perform experiments over a broad range of frequencies (10-70 cm^-1) and radiation power. We show that excitation spectra undergo significant modification when energies of microwave frequencies and lattice vibrations coincide. We argue that the effects observed are induced by parametric resonance between electronic excitations and phonons.