Optical Study of the Electronic Structure and Lattice Dynamics of NdBaMn2O6 Single Crystals

Abstract

We investigated the electronic structure and lattice dynamics of double perovskite NdBaMn2O6 single crystals through spectroscopic ellipsometry and Raman scattering spectroscopy. The optical absorption band centered at approximately 0.88 eV was assigned to on-site d–d transitions in Mn, whereas the optical feature at approximately 4.10 eV was assigned to charge-transfer transitions between the 2p state of O and 3d state of Mn. Analysis of the temperature dependence of the d-d transition indicated anomalies at 290 and 235 K. The activated phonon mode, which appeared at approximately 440 cm−1 alongside with the enhancement of the 270 cm−1 phonon mode, coupled strongly to the metal–insulator transition at 290 K, which was associated with a charge/orbital ordering. Moreover, the MnO6 octahedral breathing mode at 610 cm−1 exhibited softening at a temperature lower than 235 K (temperature of the antiferromagnetic phase transition), which revealed the strong coupling between the lattice and magnetic degrees of freedom. The spin–phonon coupling constant obtained was λ = 2.5 cm−1. These findings highlight the importance of charge–orbital–spin interactions in establishing NdBaMn2O6 phases with novel properties.

Structure and phase transitions in A -site ordered RBaMn2O6 ( R<

“…Accordingly, the octahedral coordination of Mn is composed of four short distances (around 1.92 Å) and two long ones (about 2.02 Å) but the geometric arrangement has nothing to do with a Jahn-Teller distortion so that the ferroic OO of 3d x 2 −y 2 e g orbitals in this compound at low temperature is very unlikely. On the other hand, the approximation of two basal oxygens to the Mn atom suggests an increase in the covalence of these bonds in agreement with previous spectroscopic studies on a related compound [24]. The refined structural parameters are summarized in Table II and the fits are shown in Fig.…”

“…However, the magnetic transition temperature is lowered down to 235 K on the basis of the temperature dependence of the anisotropic magnetic susceptibility curves. In this way, spectroscopic ellipsometry and Raman scattering spectroscopy also detected anomalies asso-ciated with the electric and magnetic transitions at 290 and 235 K, respectively [24]. Significant charge transfer between O 2p and Mn 3d states was also found.…”

“…To elucidate the possible presence of a symmetry center in the low-temperature phases of NdBaMn 2 O 6 and PrBaMn 2 O 6 , we have performed variable-temperature Raman measurements in the single-crystalline samples grown by the FZ technique. Not many studies have been made for PrBaMn 2 O 6 and reports [24] for NdBaMn 2 O 6 are not conclusive in this respect.…”

Anomalous boron isotope effects on electronic structure and lattice dynamics of CuB2O4

“…Only a single angle of incidence was possible because of the 70 angle of the two cryostat windows. 21 The micro-Raman scattering spectra were measured in a backscattering conguration using a laser with an excitation wavelength of 488 nm and a SENTERRA spectrometer with a 1024-pixel-wide charge-coupled detector. The spectral resolution using this spectrometer was typically lower than 0.5 cm À1 , and the laser power was lower than 4.0 mW to avoid heating effects.…”

“…In this Porto notation, the direction parallel to the crystallographic (c) axis was labelled as Z, whereas the [ 110] crystal direction was labelled as X 0 . The sample was placed in a continuous-ow helium cryostat, which enabled measurements in the temperature range of 10-300 K. 21…”