Micro-Raman study and phase transitions of Nd_0.5Ca_0.5MnO₃

Abstract

A micro-Raman study of high quality Nd0.5Ca0.5MnO3 single crystals is presented, with temperature variation. Twelve Ag and eight B2g Raman active modes (simplified symmetry: Pmma space group) have been observed in resonance conditions and compared to the parent and charge ordered compound phonons. The detected Nd0.5Ca0.5MnO3 phonons retrace the magnetic and structural temperature evolutions in the paramagnetic, charge ordered (Tco∼250 K) and antiferromagnetic orbital ordered (TN∼160 K) regimes. In particular, at T<TN, phase separation and also rotational and coherent Jahn–Teller MnO6 distortions prevail.

Detecting charge and lattice dynamics in photoinduced charge-order melting in perovskite-type manganites using a 30-femtosecond time resolution

“…The polarizations of incident and scattered lights are perpendicular to the c axis and the direction of the incident and scattered lights is parallel to the ab plane. The results are almost identical to those previously reported by Jandl et al, 26 although they did not measure the spectra below 100 cm −1 .…”

“…[24][25][26][27][28] Figure 5͑a͒ shows the temperature variation in Raman spectra for Nd 0.5 Ca 0.5 MnO 3 . The polarizations of incident and scattered lights are perpendicular to the c axis and the direction of the incident and scattered lights is parallel to the ab plane.…”

Observation of charge ordering by Raman scattering in Nd0.5Ca0.5MnO3thin films

“…In contrast to the Pr 0.5 Ca 0.5 MnO 3 [27] and La 0.5 Ca 0.5 MnO 3 [29] thin films grown on STO and LAO substrates where orbital ordering is not detected by Raman scattering, such a lowtemperature phase is clearly observed in our NCMO/LAO and NCMO/STO thin films as their counterpart in single crystals [23] with new modes appearing as the symmetry of the crystal structure is lowered through the transition. Furthermore, no local modes that would be associated with defects or oxygen non-stoichiometry are observed in our NCMO/LAO and NCMO/STO thin films, in contrast also to a few unidentified excitations in the same previous Raman studies of PCMO and LCMO thin films [27,29].…”

“…is Pnma and three excitations are observed at around 264, 300 and 458 cm −1 in the 2000 Å NCMO/LAO thin-film paramagnetic phase (figure 3). These correspond to the ∼265 cm −1 (A g ), 290 cm −1 (A g ) and 440 cm −1 (B 2g ) excitations observed in the singlecrystal paramagnetic phase [23]. Such bands have been associated with the insulating hightemperature phase of the manganite's rotation-like mode (∼250 cm −1 ) which measures the rotational and the Jahn-Teller (∼450 cm −1 ) distortions, respectively [17].…”

“…In particular, Asselin et al [22] have shown that the Raman-active phonons of a single crystal of Nd 0.5 Sr 0.5 MnO 3 retrace the evolutions between the paramagnetic, ferromagnetic, A-type antiferromagnetic and CE-type antiferromagnetic charge and orbital ordering phase transitions. Recently, Jandl et al [23] have studied bulk Nd 0.5 Ca 0.5 MnO 3 phase transitions in the paramagnetic, charge-ordered (T co ∼ 250 K) and antiferromagnetic orbital-ordered (T N ∼ 160 K) regimes by the micro-Raman technique. At T < T N , the CE-type phase dominates and 20 Raman-active modes have been detected and compared to NdMnO 3 [24], CaMnO 3 [25], Nd 0.5 Sr 0.5 MnO 3 [22] and La 0.5 Ca 0.5 MnO 3 [26] low-temperature phonon frequencies.…”