  We have performed Raman scattering measurements on BiFeO3 nanoparticles and
studied both magnetic and lattice modes. We reveal strong anomalies between 140
K and 200 K in the frequency of magnon and E(LO1), E(TO1) and A1(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 the cycloid periodicity.
