Collective phase-like mode and the role of lattice distortions atT_N∼T_Cin RMn₂O₅(R= Pr, Sm, Gd, Tb, Bi)

Abstract

We report on electronic collective excitations in RMn 2 O 5 (R= Pr, Sm, Gd, Tb) showing condensation starting at and below ~T N~TC~4 0-50 K. Its origin is understood as partial delocalized e g electron orbitals in the Jahn-Teller distortion of the pyramids dimmer with strong hybridized Mn 3+ -O bonds. Our local probes, Raman, infrared, and X-ray absorption, back the conclusion by which there is no structural phase transition at T N~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.

Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO3

“…They may hint JT lattice distortion enhancements contributing to local structural modifications due to the magnetoelastic volume contraction at ~78 K. At this respect is worth noticing that in the context of orbital physics Saitoh et al [20] pointed that similar shoulder behavior, but from Mn-O stretching bond in LaMnO 3 , were bound to appear as due to a zone boundary phonon folded back to k≈0 in the orbital ordered state. This kind of mode, that was observed by us in RMn 2 O 5 [21] and reported anomalous in TbMn 2 O 5 [22], does not seem to have a direct counterpart in NdMnO 3 .…”

“…A transmission (absorption) spectrum peaking at a transverse optical (TO) mode will yield, at higher frequencies than the TO, a featureless background missing most of the information on longitudinal (and collective) excitations [52] as we have found for temperatures above T N in NdMnO 3 (Fig. 6 a; also [21]). This is also supported by our preliminary results on hexagonal TmMnO 3 , which show the low frequency collective excitation and magnetoelectric couplings playing a main role.…”

“…(Fig. 6 a; also [21]). This is also supported by our preliminary results on hexagonal TmMnO 3 , which show the low frequency collective excitation and magnetoelectric couplings playing a main role.…”

Anomalous multi-order Raman scattering in LaMnO3: a signature of quantum lattice effects in a Jahn–Teller crystal

“…The mode intensity increases with decreasing temperature in the low-temperature magnetic phase, where it can be suppressed by an external z-axis polarised magnetic field of an order of several Tesla [49]. In multiferroics of more complex mixed-valence manganites of RMn 2 O 5 (R=Pr,Sm,Gd,Tb) a strong featureless band around these frequencies in the infrared reflectivity spectra was associated with collective electronic excitations of partially delocalised e g electronic orbitals, participating in dynamical multiferroic coupling in the Jahn-Teller distortion of the pyramid dimer [50]. The transmission measurements detected this mode in TbMn 2 O 5 and YMn 2 O 5 at 9.6 cm −1 and 7.2 cm −1 , respectively [51].…”