We present near edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges
to investigate the relative sensitivity of the edges to bonding and structure. Collectively, the spectra probe
local electronic structure and intermediate range crystal structure. Spin independent full multiple scattering
calculations of the Mn K edge give good agreement with data above threshold and qualitatively reproduce
the prepeak that is observed for each compound. We show that the apparent prepeak for MnO is not due to
p−d hybridization at the Mn atom (in accordance with symmetry principles) or quadrupolar transitions but
originates from multiple scattering within the fifth shell. We present spin dependent multiple scattering
calculations of the O K edge and show that this edge allows for a more direct description of the 3d states than
either the Mn L edge or K edge prepeak, which are complicated by multiplet effects.
The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder) and Peierls (localization via distortion of a periodic 1D lattice). One additional route to a MIT proposed by Slater, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention. Using neutron and X-ray scattering we show that the MIT in NaOsO3 is coincident with the onset of long-range commensurate three dimensional magnetic order. Whilst candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT. We discuss our results in the light of recent reports of a Mott spin-orbit insulating state in other 5d oxides.
The electronic structure and magnetism of Ir 5d5 states in nonmetallic, weakly ferromagnetic BaIrO3 are probed with x-ray absorption techniques. Contrary to expectation, the Ir 5d orbital moment is found to be ~1.5 times larger than the spin moment. This unusual, atomiclike nature of the 5d moment is driven by a strong spin-orbit interaction in heavy Ir ions, as confirmed by the nonstatistical large branching ratio at Ir L(2,3) absorption edges. As a consequence, orbital interactions cannot be neglected when addressing the nature of magnetic ordering in BaIrO3. The local moment behavior persists even as the metallic-paramagnetic phase boundary is approached with Sr doping or applied pressure.
The authors present a systematic study of high-pressure effects on electronic structure and magnetism in 3d transition metals (Fe, Co, and Ni) based on x-ray magnetic circular dichroism measurements. The data show that the net magnetic moment in Fe vanishes above 18GPa upon the transition to hcp Fe, while both cobalt and nickel remain ferromagnetic to well over 100GPa. The authors estimate the total disappearance of moment in hcp Co at around 150GPa and predict a nonmagnetic Ni phase above 250GPa. The present data suggest that the suppression of ferromagnetism in Fe, Co, and Ni is due to pressure-induced broadening of the 3d valence bands.
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