Raman scattering inFeBO3at high pressures: Phonon coupled to spin-pair fluctuations and magneto-deformation potentials

The first direct measurement of the modulation of the magnetic superexchange parameter J by optical phonons is reported. High-pressure Raman scattering studies of the model compound ${\mathrm{FeBO}}_3$ reveal an unexpectedly large interaction between a (${\mathrm{BO}}_3$ ${)}^{3\mathrm{-}}$ internal mode and spin-pair excitations. By pressure tuning J, resonant decay of the phonon into the two-magnon continuum and associated mixing were observed yielding a phonon-magnon-pair coupling constant g≊(0.15–0.20)J.