B. N. Lin

Co K-edge XANES and spin-state transition of RCoO3 (R=La, Eu)

Abstract Co K-edge X-ray absorption near-edge spectra at 300 K and magnetic studies for the rhombohedral LaCoO3 with low-spin state to intermediate-spin (IS) state transition T s ≃105 K and orthorhombic EuCoO 3 (T s ≃295 K ) are reported. The small pre-edge feature observed is from 1s–3d dipole transition, which is weakly allowed through the hybridization of Co 4p states with 3d states of neighboring Co atoms. For both samples in the IS state, pre-edge can be fitted using three peaks with energy separation P 2 − P 1 =2.0 eV for R=La and Eu, and P 3 − P 2 =1.5 eV for R=La and 1.3 eV for R=Eu. Since the thermally excited IS state is a mixed t2g5eg1 and d 7 L ( t 2 g 6 e g 1 or t2g5eg2), with almost filled t2g↑ states. From reported band structure calculation, the three peaks P1, P2, P3 are probably corresponding to the unfilled t2g↓, eg↑ and eg↓ states, respectively.

Evidence of d-wave behavior in Pr1.85Ce0.15CuO3.97 aligned superconductors

Abstract The c -axis and in-plane alignment of 23 K Pr 1.85 Ce 0.15 CuO 3.97 superconducting powder were achieved with powder/epoxy cylindrical holder perpendicular and parallel to the alignment field. The temperature dependencies of basal-plane penetration depth λ ab ( T ) and c -axis Josephson penetration depth λ c ( T ) were derived using zero-field-cooled diamagnetic susceptibility χ d ( T ) in a low applied field ( B a H c1 ) parallel or perpendicular to the aligned powder where small Pr Curie–Weiss paramagnetic susceptibility χ p ( T ) was subtracted. Up to 0.5 T c , Δλ ab ( T )= λ ab ( T )− λ ab (0) as well as Josephson Δλ c ( T ) can be well fitted with a d-wave-like power law c 2 T 2 + c 4 T 4 , where T 2 -term is dominated below 0.3 T c . The present result agrees with recent phase-sensitive experiment, which indicates d-wave nature for electron-doped R 1.85 Ce 0.15 CuO 4− δ (R=Pr, Nd) cuprates.

Mn K-edge XANES of hexagonal manganites RMnO3 (R = Sc, Y)

Abstract Mn K-edge X-ray absorption near-edge spectra (XANES) and magnetic studies for ferroelectromagnetic compounds RMnO3 (R=Sc,Y) are reported. ScMnO3 shows stronger d–p hybridization with a triangular antiferromagnetic (AF) order of T N =133 K and a spin reorientation T sr =23 K , as compared to T N =74 K for YMnO3. The identical main threshold edge energy of 6545 eV indicates Mn3+ character. Small pre-edge features with energy separation P2–P1 of 2.27 eV for ScMnO3 and 2.72 eV for YMnO3 is from the 1s–3d dipole transition, which is weakly allowed through the hybridization of Mn 4p with 3d states of neighboring Mn atoms. The larger P1 peak is corresponding to transition into empty e↓′ and e↓″ minority states, and the smaller P2 peak is into leftover e↓′ states.

Metal-Insulator Transition and Cu K-Edge XANES Studies for Pr1.85Ce0.15CuO4+δ High-Tc Superconductors

AbstractMetal-insulator transition near oxygen content parameter δ∼−0.018 was observed for electron-doped Pr1.85Ce0.15CuO4+δ (−0.003≤δ≤0.03) cuprates. Cu K-edge X-ray absorption near-edge structure (XANES) studies with nearly identical threshold edge energy E0 of 8980.8 eV indicate a Cu formal valence smaller than 2 for all samples, which is consistent with the estimated Cu valence of ∼1.84 for 20.5 K superconductor Pr1.85Ce0.15CuO3.997 and ∼1.91 for Pr1.85Ce0.15CuO4.03 insulator. The XANES spectrum reflects the Cu 3dn character where low energy peak A1 reflects the 3d10 configuration of Cu(I) oxidation state and A2 peak reflects the 3d10

Unusual Pr antiferromagnetic ordering in high-Tc cuprates

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Crystallographic and physical properties of new orthorhombic Cu-1212 R(Ba2−xR′x)Cu3O7+y system (R, R′La, Pr, Nd; 0.65<x<1)

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2D ferromagnetic fluctuation above TN in orbital-ordered LaMnO3

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