Effect of Co, Ni, and Cu substitution on the electronic structure of hexagonal YMnO3 studied by x-ray absorption spectroscopy

Abstract

X-ray absorption spectroscopy measurements have been performed to elucidate local electronic and atomic structures of orthorhombic 3d-transition metal-doped yttrium manganites ͑YMnO 3 ͒ with chemical formulae YMn 2/3 Me 1/3 O 3 ͑Me= Co, Ni, and Cu͒. The Mn L 3 -and K-edges x-ray absorption near-edge structure ͑XANES͒ demonstrate the direct substitution of Me 2+ for Mn 3+ , so that the positive effective charge of Mn ions are increased. Me-doping is also found to induce substantial broadening of the Mn L 3 -edge feature, which suggests enhancement of the delocalization of Mn 3d e g subbands and conductivity. Local spin density approximation ͑LSDA͒ +U ͑Hubbard U parameter͒ calculations were used to understand their electronic structures.

Electronic structure of RuSr2EuCu2O8studied by x-ray absorption and photoemission spectroscopies

“…These features provide detailed information about unoccupied O 2p-derived states or hole concentration of O 2p character commonly observed in perovskite oxides and ruthenocuprates. [17][18][19][20][21][22] The general line shapes of the features a 1 -c 1 of RuEu-1212 differ significantly from those of reference SRO, all of which are magnified in Ru e g band. The energy separation between the Ru t 2g band (∼528 eV) and the center of the e g band (∼531 eV) (with a crystal field splitting, = 10 D q ) is approximately 3 eV in agreement with that obtained from the Ru L 3 -edge XANES spectra to be shown later.…”

“…The thresholds of the Cu K-edge XANES spectra of Cu oxides with a Cu 2+δ charge state have been observed to shift to higher energy relative to that of Cu 2+ if δ is not too small. 17 However, no energy shift was observed in the Cu K-edge XANES spectra of RuEu-1212 relative to that of CuO (Cu 2+ ) at temperatures from RT down to 25 K, as illustrated in Fig. 6(a), suggestive of a small δ value.…”

Anisotropy in the thermal hysteresis of resistivity and charge density wave nature of single crystal SrFeO3-δ: X-ray absorption and photoemission studies

“…The anisotropy or direction-dependence of resistivity in the thermal hysteresis region of a single crystal of SrFeO 2.81 is not mostly explained by the coexistence of antiferromagnetic and paramagnetic phases, by the incommensurate-to-commensurate CO transition 5, 6, 13 , or in terms of the charge-disproportionation or CDW state 3, 19 . Several theoretical and experimental studies of single crystals and thin films of various materials have established that the anisotropy of resistivity is associated with OO or with the preferential occupation of orbitals, is primarily controlled by doping or lattice distortion/strains 21, 23, 26, 29–33 . Accordingly, the anisotropy of resistivity both in the ab -plane and along the c -axis in SrFeO 2.81 crystal in the thermal hysteresis region is closely related to the changes in electronic and lattice structures.

Figure 2Temperature-dependence of resistivity of a single crystal of SrFeO 2.81 , measured in ab -plane and along c -axis.

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Robustness of magnetic and electric domains against charge carrier doping in multiferroic hexagonal ErMnO3

“…This is strikingly reflected by extrinsic semiconductors that owe their specific n-or p-type properties to implanted defects [15]. Following the same idea, different ionic impurities have been introduced to RMnO 3 systems with the goal to improve their magnetic response [16,17] or electronic conductance [18]. It remains unclear, however, to what extent chemical doping affects the topology and functionality of the ferroelectric and antiferromagnetic domains as spatially resolved studies are virtually non-existent.…”