CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
congresos y reuniones científicas
Collective Phase Mode and the Role of Lattice Distortions at TN~TC in XMn2O5 (X= Bi, Pr, Sm, Gd, Tb),
N. E. MASSA; A. F. GARCÍA FLORES; E. GRANADO; G.F.L. FABBRIS; G. DE M. AZEVEDO; L. DEL CAMPO; D. DE SOUSA MENESES; P. ECHEGUT; M. J. MARTINEZ-LOPE; J. A. ALONSO
Congreso; American Physical Society March Meeting; 2011
American Physical Society
We report on detailed temperature dependent infrared reflectivity, Raman, local structure, and X-ray diffraction measurements of multiferroic XMn2O5 (X= Bi, Pr, Sm, Gd, Tb). While for BiMn2O5 there are weak but distinct spectroscopic changes that together with high resolution diffraction patterns suggest a lattice role at TN~TC, for the rare earth (R) replaced infrared spectra have as a main feature a broad band at meV energies in addition to progressive rotation of Mn-O polyhedra. That band, independent of the R3+ ion size and common to all, suggests hopping of carriers through fluctuations at a local scale. It partially condenses below 40 K, i.e., the collective electronic behavior changes from delocalized to one partially localized. We assimilate that condensate to a CDW-like phase mode. It might indicate induced orbital correlation of charge transfers between Mn sites.Frequency Raman phonon shifts are observed at T~60 K, due to spin-phonon coupling, and at TN~TC. Below TN~TC there is no a Raman soft mode that might be associated to a CDW amplitude mode