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2012
ACL
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N.E.Massa, A.F.García-Flores, D.De Sousa Meneses, L.del Campo, P.Echegut, G.F.L.Fabbris, M.J.Martínez-Lope, J.A.Alonso, 'Collective phase-like mode and the role of lattice distortions at TN ~ TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi)', J. Phys. Cond. Mat. 24 195601-195611 (2012) doi:10.1088/0953-8984/24/19/195901
We report on electronic collective excitations in RMn2O5 (R=Pr, Sm, Gd, Tb) showing condensation starting at and below ~ TN ~TC~40–50 K. Their origin is understood as partial delocalized eg electron orbitals in the Jahn–Teller distortion of the pyramid dimer with strong hybridized Mn3C–O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at TN~TC. Ferroelectricity is magnetically assisted by electron localization triggering lattice polarizability by unscreening. We have also found phonon hardening as the rare earth is sequentially replaced. This is understood as a consequence of lanthanide contraction. It is suggested that partially f-electron screened rare earth nuclei might be introducing a perturbation to eg electrons prone to delocalize as the superexchange interaction takes place.
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