Temperature-Dependent Raman Scattering of Multiferroic Pb(Fe_1/2Nb_1/2)O₃

Raman scattering measurements on multiferroic Pb(Fe _1/2 Nb _1/2 )O ₃ 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 B O ₆ 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 ^* .