Impact Of The Surface Phase Transition On Magnon And Phonon Excitations In Bifeo3 Nanoparticles

We have performed Raman scattering measurements on bismuth ferrite (BiFeO3) nanoparticles and studied both magnetic and lattice modes. We reveal strong anomalies between 140K and 200K at the frequency of magnon and E(LO1), E(TO1), and A(1)(LO1) phonon modes. These anomalies are related to a surface expansion and are enhanced for nanoparticle sizes approaching the spin cycloidal length. These observations point out the strong interplay between the surface, the lattice, and the magnetism for sizes of BiFeO3 nanoparticles close to cycloid periodicity.