Role of Jahn-Teller disorder in Raman scattering of mixed-valence manganites

Abstract

The mixed-valence perovskitelike manganites are characterized by the unique interrelation of Jahn-Teller distortions, electric and magnetic properties. The Jahn-Teller distortion follows the Mn 3ϩ →Mn 4ϩ charge transfer with some delay. Its development depends on the lifetime of Mn in the 3ϩ state, governed by the Mn 4ϩ /Mn 3ϩ ratio and magnetic correlations. The noncoherence of Jahn-Teller distortions in orthorhombic mixed-valence manganites and rhombohedral RMnO 3 (Rϭrare earth͒ results in oxygen disorder. We demonstrate that the Raman spectra in this case are dominated by disorder-induced bands, reflecting the oxygen partial phonon density of states ͑PDOS͒. The PDOS origin of the main Raman bands in insulating phases of such compounds is evidenced by the similar line shape of experimental spectra and calculated smeared PDOS and disappearance of the PDOS bands in the ordered ferromagnetic metallic phase.

Raman spectra in epitaxial thin films ofLa1−xCaxMnO3(Xiong1, Chen2, Wang3 et al. 2004Phys. Rev. B502232View full textAdd to dashboardCite

“…While a tensile strain affects the lattice strongly. These sharp peaks in the 400 to 500 cm −1 range always appear together in the Raman spectra of LCMO 37,41,43,45,46 . Based on their similar behavior with the temperature and substrates in our case and the earlier reports in films and bulk samples 37,41 , we attribute these narrow peaks to the same symmetry.…”

“…It has been reported in bulk samples that the distorted volume reaches its maximum for disordered M n 3+ /M n 4+ composition with ∼ 30 % M n 4+ . 46 The decrease in intensity of the disorder-induced bands at higher doping and the appearance of some sharp Raman features can be explained by increasing the volume of domains with short-range charge/orbital-ordered 32 . As reported in bulk sample of La 0.5 Ca 0.5 M nO 3 , Raman structures are weak at room temperature, the structure at ∼ 480 and ∼ 600 cm −1 develop and become strong with decreasing temperature below CO temperature.…”

“…These sharp peaks may be correlated with the electron or spin excitations existing in the metallic-state phase. Recently, another explanation was reported that these much sharper Raman lines corresponding to the Γ-point Raman phonon of the ordered structure reflects the disorder-order transition, concomitant with the PM to FM and insulatormetal transitions 46 . However, no sharp peaks appear when the sample enters FM state in the film on STO.…”

“…According to the previous reports, the Raman feature ω 2 could contain several peaks with different symmetry 36,43,46 , its temperature dependence is com-plex due to the overlap of these modes. The different temperature behaviors of these modes induce a shift of the broad ω 2 band.…”

Large low field magnetoresistance in La0.67Sr0.33MnO3 nanowire devices

“…17 For the x = 0.10 and 0.33, the B 2g peak is shifted to around at 670 cm −1 and its intensity decreases. There are published reports [18][19][20] stating that rhombohedral structure does not show any broadbands between 580 and 680 cm −1 but distorted orthorhombic structure does display a peak 19 around 670 cm −1 . It is worth noting that all the samples were kept in high vacuum to avoid surface oxidation that may produce the artificial distorted signals pointed out by Granado et al…”