The effect of orbital-lattice coupling on the electrical resistivity of YBaCuFeO5 investigated by X-ray absorption

M K Srivastava,S H Hsieh,H J Lin,K Asokan,C W Pao,Y Y Chin,X.-S Qiu,W F Pong,C.-H Lai,Y C Lai,Y.-H Liang,J F Lee,J W Chiou,Y C Shao,C H Du,H M Tsai,H T Wang

doi:10.1038/s41598-019-54772-0

M K Srivastava, S H Hsieh + Show 15 more

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https://doi.org/10.1038/s41598-019-54772-0

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Temperature-dependent X-ray absorption near-edge structures, X-ray linear dichroism (XLD) and extended X-ray absorption fine structure (EXAFS) spectroscopic techniques were used to investigate the valence state, preferred orbital and local atomic structure that significantly affect the electrical and magnetic properties of a single crystal of YBaCuFeO5 (YBCFO). An onset of increase of resistivity at ~180 K, followed by a rapid increase at/below 125 K, is observed. An antiferromagnetic (AFM)-like transition is close to the temperature at which the resistivity starts to increase in the ab-plane and is also observed with strong anisotropy between the ab-plane and the c-axis. The XLD spectra at the Fe L3,2-edge revealed a change in Fe 3d eg holes from the preferential {bf{3}}{{boldsymbol{d}}}_{{{bf{x}}}^{{bf{2}}}{boldsymbol{-}}{{bf{y}}}^{{bf{2}}}} orbital at high temperature (300–150 K) to the {bf{3}}{{boldsymbol{d}}}_{{{bf{3}}{bf{z}}}^{{bf{2}}}{boldsymbol{-}}{{bf{r}}}^{{bf{2}}}} orbital at/below 125 K. The analysis of the Fe K-edge EXAFS data of YBCFO further revealed an unusual increase in the Debye-Waller factor of the nearest-neighbor Fe-O bond length at/below 125 K, suggesting phonon-softening behavior, resulting in the breaking of lattice symmetry, particularly in the ab-plane of Fe-related square pyramids. These findings demonstrate a close correlation between electrical resistivity and coupling of the preferred Fe 3d orbital with lattice distortion of a single crystal of YBCFO.

Highlights

Transition metal (TM) oxides with perovskite structure and general formula ABO3 (A = alkaline or rare earth metal, B = TM), and/or layered oxygen-deficient (δ) double perovskites with lower symmetry having general formula AA′B2O6-δ, or AA′BB′O6-δ (A′ = A or Lanthanides; B′ = same as B or different TM)[1,2] are well known for their fascinating physical properties such as colossal magneto-resistance, high-TC superconductivity, exhibiting a metal-to-insulator transition, multiferrocity, electrochemical properties and others[3,4,5,6,7]
A neutron study by some of the co-authors of the present work demonstrated that a single crystal of YBCFO has strongly anisotropic magnetic properties: two AFM-like transitions occur in the ab-plane and a paramagnetic-like feature along the c-axis
Fe and Cu K-edge X-ray absorption near-edge structure (XANES) indicated that the valence of Fe3+ and Cu2+ states remain constant in the ab-plane and along the c-axis of YBCFO at various temperatures

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These results further suggest phonon-softening behavior in the YBCFO, breaking of the lattice symmetry, especially in the ab-plane of the Fe-related square pyramids, accompanied by a change in the preferred Fe 3d orbital, causing an unusual increase in the electrical resistivity and anisotropic magnetic behavior at/below 125 K in a single crystal of YBCFO.

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