Magnetic and electronic Co states in the layered cobaltate GdBaCo2O5.5−x

M. Garcia-Fernandez (1) , V. Scagnoli (2) , U. Staub (1) , A. M. Mulders (3, 4) , M. Janousch (1) , Y. Bodenthin (1) , Stéphane Grenier (5) , D. Meister (1) , B. D. Patterson (1) , A. Mirone (2) , Y. Tanaka (6) , T. Nakamura (7) , Yue Huang (8) , K. Conder (9)

1 PSI - Paul Scherrer Institute
2 ESRF - European Synchrotron Radiation Facility
3 BI - The Bragg Institute, Australian Nuclear Science and Technology Organization,
4 DIAP - Department of Imaging and Applied Physics
5 NEEL - MRS - Matériaux, Rayonnements, Structure
6 RIKEN RSC - RIKEN SPring-8 Center [Hyogo]
7 JASRI - Japan Synchrotron Radiation Research Institute [Hyogo]
8 VdWZI - Van der Waals-Zeeman Instituut
9 LNS - Laboratory for Neutron Scattering and Imaging [Paul Scherrer Institute]

We have performed nonresonant x-ray diffraction, resonant soft and hard x-ray magnetic diffraction, soft x-ray absorption, and x-ray magnetic circular dichroism measurements to clarify the electronic and magnetic states of the Co3+ ions in GdBaCo2O5.5. Our data are consistent with a Co_Py³⁺ high-spin (HS) state at the pyramidal sites and a Co_Oc³⁺ low-spin (LS) state at the octahedral sites. The structural distortion with a doubling of the a axis (2ap×2ap×2ap cell) shows alternating elongations and contractions of the pyramids, and indicates that the metal-insulator transition is associated with orbital order in the t2g orbitals of the Co_Py³⁺ HS state. This distortion corresponds to an alternating ordering of xz and yz orbitals along the a and c axes for the Co_Py³⁺. The orbital ordering and pyramidal distortion lead to deformation of the octahedra but the Co_Oc³⁺ LS state does not allow an orbital order to occur for the Co_Oc³⁺ ions. The soft x-ray magnetic diffraction results indicate that the magnetic moments are aligned in the ab plane but are not parallel to the crystallographic a or b axes. The orbital order and the doubling of the magnetic unit cell along the c axis support a noncollinear magnetic structure. The x-ray magnetic circular dichroism data indicate that there is a large orbital magnetic contribution to the total ordered Co moment.

Mots clés: cobaltate; resonant x-ray scattering

Domaines: Electrons fortement corrélés [cond-mat.str-el]

M. Garcia-Fernandez, V. Scagnoli, U. Staub, A. M. Mulders, M. Janousch, et al.. Magnetic and electronic Co states in the layered cobaltate GdBaCo2O5.5−x. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2008, 78 (5), pp.054424. ⟨10.1103/PhysRevB.78.054424⟩. ⟨hal-00311689⟩