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

Abstract

The local electronic and atomic structures of the high-quality single crystal of SrFeO3-δ (δ~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L 3,2-edge X-ray linear dichroism results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d e g states remain in persistently out-of-plane 3d 3z 2 -r 2 orbitals. In contrast, in the warming process below the transition temperature, they change from 3d 3z 2 -r 2 to in-plane 3d x 2 -y 2 orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3d x 2 -y 2 and out-of-plane 3d 3z 2 -r 2 orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-δ (δ~0.19) single crystal.

Structural properties of charge disproportionation and magnetic order in Sr2/3Ln1/3FeO3 (Ln=La, Pr, and Nd)

“…Phonon condensation at T MI might relax structural strain in the environment of oxygen atoms and consequently, two nonequivalent Fe sites are formed developing a charge density wave (CDW) with a sixfold periodicity. The formation of this type of CDW is able to open a band gap as has been recently observed in the SrFeO 3-δ sample [48], very related to our compounds.…”

Anisotropy in the magnetic interaction and lattice-orbital coupling of single crystal Ni3TeO6

“…In contrast, the inherent distortion of NiO 6 octahedra stabilizes the Ni 3 d 3z 2 −r 2 orbital above T SO . Phonon-softening behavior and, consequently, anomalous DWF behavior in the ab -plane below a transition temperature were recently observed in our study of a SrFeO 3−δ single crystal 45 . A detailed theoretical investigation must be conducted in the future to develop our understanding of the correlation between local lattice distortion and preferential orbital occupation and its effect on the spin-spin correlation function in the NTO single crystal.…”

“…5(a) displays the temperature-dependent Ni L 3,2 -edge XLD (difference in the XANES features between E // c and E ⊥ c ) of NTO. The alignment of the X-ray electric polarization field E , both out-of-plane ( E // c ) and in-plane ( E ⊥ c ), and Ni L 3,2 -edge XLD allow probing of the corresponding unoccupied Ni e g 3 d 3z 2 −r 2 and 3 d x 2 −y 2 orbitals (or the parallel and perpendicular projections onto the crystallographic c -axis in the present NTO system), respectively 20,45,48 . The sign of the XLD spectra is negative in the paramagnetic regime (above 60 K), indicating that the Ni e g holes preferentially occupy 3 d x 2 −y 2 (that is, preferential occupancy of the Ni e g electrons in 3 d 3z 2 −r 2 ) orbitals.…”

“…The evolution of this anisotropic behavior can also be attributed to an additional local CF effect and ligand-metal p-d hybridization, which stabilize electron occupancy in the 3 d 3z 2 −r 2 orbitals in the NTO. Although the origin of this CF effect and ligand-metal p-d hybridization is currently not considered, the distortion of the crystal structure is primarily responsible for the lowering of the energy of either the in-plane or out-of-plane e g orbitals of transition metal oxides 45 . We believe that the inherent distortion of NiO 6 octahedra in an environment of trigonal symmetry also plays an important role, just as VO 6 octahedral distortion contributes importantly to orbit-lattice coupling in rare-earth vanadates 24,25 .…”

Кислородные вакансии и валентные состояния железа в соединениях SrFeO-=SUB=-3-delta-=/SUB=-

“…Композиции материала сильно зависят от содержания кислорода. Согласно литературным данным [4][5][6][7][8][9][10], в кислороднодефицитном феррите стронция SrFeO 3−δ существуют четыре однофазные структуры: SrFeO 3 (кубическая сингония), SrFeO 2.86 (тетрагональная), SrFeO 2.73 (ромбическая) и SrFeO 2.50 (ромбическая, тип браунмиллерит). Эти однофазные структуры описываются общей схемой, предложенной в работе [4]: SrFeO 3−1/n (n = ∞, 8, 4, 2), где на одну вакансию приходится n исходных перовскитных ячеек.…”