Misfit strain-induced changes in the Fe-sublattice of multiferroic Pb(Fe1/2Nb1/2)O3 epitaxial nanofilm seen via Raman spectroscopy

Magnetic phase transition temperature of the PbFe1/2Nb1/2O3 (PFN) nanofilm on the SrTiO3 substrate was reported to be about 50 K higher than that in the bulk samples. We carried out comparative Raman studies of a 90 nm-thick PFN epitaxial film on SrRuO3-buffered (001) SrTiO3 substrate and the bulk samples of ceramic PFN and a single crystal. It was found out that the bands at ≈250 cm−1 and ≈700 cm−1 in the spectrum of the film, corresponding to FeO vibrational modes, are shifted by about 20 cm−1 to higher frequencies as compared to the bulk samples. This result is in line with the predictions of the recent first-principles calculations that compressive misfit strain stimulates the disorder in the Fe and Nb distribution in the lattice, leading to an increase of the magnetic phase transition temperature. Such disordering might cause the changes in the Fe-sublattice of PFN seen in the Raman spectrum.