Raman studies of spin-phonon coupling in hexagonal BaFe₁₂O ₁₉

Phonon softening in hexagonal BaFe₁₂O₁₉ single crystal is observed in temperature dependent polarized Raman spectroscopy. The phonon softening is significantly enhanced below ∼80 K, at which the magnetization in a magnetic field along c-axis shows a clear change in the temperature dependence, indicating a magnetic phase transition near 80 K. Possible interpretations of the anomalous temperature dependence of the phonon frequencies-phonon softening behaviors are discussed. The phonon softening would be correlated to local structural and magnetic phase transition in hexagonal BaFe₁₂O₁₉, in which the spin-phonon coupling would have major contribution for the phonon softening. We also discuss that the spin-phonon coupling would be affected by both the spin ordering and the individual phonon vibration in magnetic material.