Valence, spin, and orbital state of Co ions in one-dimensional Ca3Co2O6: An x-ray absorption and magnetic circular dichroism study

Tobias Burnus,1 Zhiwei Hu,1 Maurits W. Haverkort,1 Júlio C. Cezar,2 Delphine Flahaut,3 Vincent Hardy,3 Antoine Maignan,3 Nicholas B. Brookes,2 Arata Tanaka,4 Hui-Huang Hsieh,5 Hong-Ji Lin,6 Chien-Te Chen6 and L. Hao Tjeng1

1 II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
2European Synchrotron Radiation Facility, Boîte Postale 220, Grenoble 38043, France
3Laboratoire CRISMAT, UMR 6508, ENSICAEN/CNRS, Université de Caen, 6, Boulevard du Maréchal Juin, 14050 Caen Cedex, France
4Laboratoire CRISMAT, UMR 6508, Institut des Sciences de la Matière et du Rayonnement, Université de Caen, 6, Boulevard du Maréchal Juin, 14050 Caen Cedex, France
5Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
6Chung Cheng Institute of Technology, National Defense University, Taoyuan 335, Taiwan
7National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30077, Taiwan

[Abstract][References]

Abstract

We have investigated the valence, spin, and orbital state of the Co ions in the one-dimensional cobaltate Ca3Co2O6 using x-ray absorption and x-ray magnetic circular dichroism at the Co-L2,3 edges. The Co ions at both the octahedral Cooct and trigonal Cotrig sites are found to be in a 3+ state. From the analysis of the dichroism we established a low-spin state for the Cooct and a high-spin state with an anomalously large orbital moment of 1.7μB at the Co3+ trig ions. This large orbital moment along the c-axis chain and the unusually large magnetocrystalline anisotropy can be traced back to the double occupancy of the d2 orbital in trigonal crystal field.

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