Raman scattering studies of hexagonal rare-earth RMnO₃ (R = Tb, Dy, Ho, Er) thin films

We have studied the rare-earth (R) dependence of the phonon and magnon scattering in hexagonal RMnO₃ (R = Tb, Dy, Ho, Er) thin films using Raman scattering spectroscopy. We found, as the ionic radius of R decreases from Tb to Er, the phonons shift to higher energies. Our results indicate that both the lattice constants a and c of hexagonal RMnO₃ would decrease when the ionic radius of R decreases, and the lattice constant c would have a weaker R dependence. The magnons also shift to higher energies when the radius of the R ion decreases, and they show faster upshift than the phonons. In addition, the Néel temperature also shows a systematic increasing behavior when the radius of the R ion decreases. The dependence of the rare-earth R on the magnons and the Néel temperature can be explained by the rapid increase of the spin-exchange integral when the Mn-Mn distance decreases.