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MA: Fachverband Magnetismus

MA 38: Multiferroics

MA 38.4: Vortrag

Donnerstag, 26. März 2009, 16:00–16:15, HSZ 103

Ising magnetism and ferroelectricity in Ca₃CoMnO₆ — •Hua Wu¹, T. Burnus¹, Z. Hu¹, C. Martin², A. Maignan², J. C. Cezar³, A. Tanaka⁴, N. B. Brookes³, D. I. Khomskii¹, and L. H. Tjeng¹ — ¹II. Phys. Inst, Uni Köln — ²Lab. CRISMAT, Caen, France — ³ESRF Grenoble, France — ⁴Hiroshima University, Japan

Among a variety of multiferroic materials discovered so far, see review articles [1,2], ferroelectric Ising chain magnet Ca₃CoMnO₆ is quite unique, because the ferroelectricity is driven by a magnetostriction in a collinear Ising spin chain consisting of the charge ordered transition-metal ions [3]. In this work, the origin of both the Ising chain magnetism and ferroelectricity in Ca₃CoMnO₆ is studied by ab initio electronic structure calculations and x-ray absorption spectroscopy. We find that Ca₃CoMnO₆ has the alternate trigonal prismatic Co²⁺ and octahedral Mn⁴⁺ sites in the spin chain. Both the Co²⁺ and Mn⁴⁺ are in the high spin state. In addition, the Co²⁺ has a huge orbital moment of 1.7 µ_B which is responsible for the significant Ising magnetism. The centrosymmetric crystal structure known so far is calculated to be unstable with respect to magnetostriction in the experimentally observed ↑↑↓↓ antiferromagnetic structure for the Ising chain. The calculated inequivalence of the Co-Mn distances accounts for the ferroelectricity.
S. W. Cheong and M. Mostovoy, Nat. Mater. 6, 13 (2007). [2] D. I. Khomskii, J. Magn. Magn. Mater. 306, 1 (2006). [3] Y. J. Choi et al. Phys. Rev. Lett. 100, 047601 (2008).