Magnetic and electronic co states in the layered cobaltate GdBaCo2O5.5-x

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American Physical Society
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 high-spin (HS) state at the states of the Co3+, ions in GdBaCo2O5.5. Our data are consistent with a Co-Py(3+) pyramidal sites and a Co-Oc(3+), low-spin (LS) state at the octahedral sites. The structural distortion with a doubling of the a axis (2a(p)X2a(p)X2a(p) cell) shows alternating elongations and contractions of the pyramids, and indicates that the metal-insulator transition is associated with orbital order in the t(2g) orbitals of the Co-Py(3+) HS state. This distortion corresponds to an alternating ordering of xz and yz orbitals along the a and c axes for the Co-Py(3+). The orbital ordering and pyramidal distortion lead to deformation of the octahedra but the Co-Oc(3+) LS state does not allow an orbital order to occur for the Co-Oc(3+), 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. © 2008, American Physical Society
Scattering, Diffraction, High spin states, Magnetic moments, X-ray sources, Electronic structure
García-Fernández, M., Scaunoli, V., Staub, U., Mulders, A. M., Janousch, M., Bodenthin, Y., Meister, D., Patterson, B. D., Mirone, A., Tanaka, Y., Nakamura, T., Grenier, S., Huang, Y. J., & Conder, K. (2008). Magnetic and electronic co states in the layered cobaltate GdBaCo2O5.5-x. Physical Review B, 78(5), 13. doi:10.1103/PhysRevB.78.054424