Optical spectroscopy of charge transfer transitions in multiferroic manganites, ferrites, and related insulators

Abstract

The results of theoretical and experimental studies of charge transfer (CT) transitions in multiferroic manganites, ferrites, and related insulators are reviewed. Starting with a simple cluster model approach one-center p-d and two-center d-d CT transitions, their polarization properties, the role played by structural parameters, orbital mixing, and spin degree of freedom are all addressed. Optical ellipsometry data in the spectral range of 0.6–5.8eV in perovskite and hexagonal rare-earth manganites RMnO3 and in orthorhombic manganites RMn2O5 are analyzed. Two groups of iron oxides, where Fe3+ ions occupy either only octahedral positions (BiFeO3, orhoferrites RFeO3 et al.) and materials with Fe3+ ions both in octahedral and tetrahedral positions (hematite α-Fe2O3, garnets RFe5O12, lithium ferrite LiFe5O8, Ca2Fe2O5 et al.), are discussed.

Revisiting the Optical Band Gap in Epitaxial BiFeO3 Thin Films

“…Importantly, on LAO and LSAT substrates one can obtain more insight into the optical transitions in BFO, since the substrate absorption does not obscure the film response for energies up to around 4.5 eV. Indeed, as will be show later, we can identify two charge transfer transitions [41] simply from transmission data in BFO//LSAT and BFO//LAO samples.…”

“…The transmittance of STO, LSAT, and LAO substrates is shown in Figure 3a. Indeed, as will be show later, we can identify two charge transfer transitions [41] simply from transmission data in BFO//LSAT and BFO//LAO samples. [38] From the transmittance data, the optical absorption coefficient and the Tauc plot is derived (inset of Figure 3a).…”

Near-band gap electronic structure of the tetragonal rare-earth cupratesR2CuO4and the bismuth cuprateBi2Pisarev1, Павлов2, Kalashnikova3 et al. 2010Phys. Rev. BSelf Cite270110View full textAdd to dashboardCite

“…The crystal field effects and the covalency of the Cu͑3d͒-O͑2p͒ and O͑2p͒-O͑2p͒ bondings will be taken into account. 24 Figure 7 shows results of calculations. We claim that our simple cluster model based on a separated CuO 4 6− complex has a number of advantages in comparison with, for example, band models.…”

Обменные и обменно-релятивистские эффекты в возбужденных состояниях 3d-ионов в кристаллах

“…Отметим, что именно переходы с переносом заряда формируют полосу фундаментального поглощения в подавляющем числе соединений типа окислов 3d-элементов [13][14][15][16].…”