Temperature-dependent Raman scattering of multiferroic Pb(Fe1/2Nb1/2)O3

Raman scattering measurements on multiferroic Pb(Fe1/2Nb1/2)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 similar to 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* similar to 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 similar to 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*.