Temperature-dependent Raman scattering of multiferroic Pb(Fe _1/2Nb_1/2)O₃

Raman scattering measurements on multiferroic Pb(Fe_1/2Nb _1/2)O₃ over a wide temperature range from 10 to 500 K were performed. Very broad and overlapping peaks (first-order character) and a prominent high-frequency peak at∼ 1130 cm^-1, which we assign as a two-phonon peak, were observed. These features showed remarkable changes in their Raman scattering intensity and spectral shape at the characteristic temperature T^*∼ 330 K, clearly showing a structural lattice change at around T^*. The temperature dependence of some stretching vibration modes of the BO₆ units revealed an anomalous frequency shift below T_n∼ 143 K. These anomalous deviations at T_n of the phonon frequency are associated with the spin-phonon coupling mechanism. Complementary magnetic data confirmed a weak magnetic ordering at room temperature and interestingly showed an anomaly at about T ^*. These results suggest an interplay between ferroelectric, structural and magnetic degrees of freedom in PFN, starting to be significant at around T^*.