Formation of Isomorphic Ir³⁺ and Ir⁴⁺ Octamers and Spin Dimerization in the Spinel CuIr₂S₄

Author

Paolo G. Radaelli
Yoichi Horibe
Matthias J. Gutmann
Hiroki Ishibashi
Chenghsuan Chen
Richard M. Ibberson
Yasumasa Koyama
Yew San Hor, Missouri University of Science and TechnologyFollow
Valery D. Kiryukhin
Sangwook Cheong

Abstract

Inorganic compounds with the AB₂X₄ spinel structure have been studied for many years, because of their unusual physical properties. The spinel crystallographic structure, first solved by Bragg in 1915, has cations occupying both tetrahedral (A) and octahedral (B) sites. Interesting physics arises when the B-site cations become mixed in valence. Magnetite (Fe₃O₄) is a classic and still unresolved example, where the tendency to form ordered arrays of Fe²⁺ and Fe³⁺ ions competes with the topological frustration of the B-site network. The CuIr₂S₄ thiospinel is another example, well known for the presence of a metal-insulator transition at 230 K with an abrupt decrease of the electrical conductivity on cooling accompanied by the loss of localized magnetic moments. Here, we report the determination of the crystallographic structure of CuIr₂S₄ below the metal-insulator transition. Our results indicate that CuIr₂S₄ undergoes a simultaneous charge-ordering and spin-dimerization transition - a rare phenomenon in three-dimensional compounds. Remarkably, the charge-ordering pattern consists of isomorphic octamers of Ir₈³⁺S₂₄ and Ir₈⁴⁺S₂₄ (as isovalent bi-capped hexagonal rings). This extraordinary arrangement leads to an elegant description of the spinel structure, but represents an increase in complexity with respect to all the known charge-ordered structures, which are typically based on stripes, slabs or chequerboard patterns.

Recommended Citation

P. G. Radaelli and Y. Horibe and M. J. Gutmann and H. Ishibashi and C. Chen and R. M. Ibberson and Y. Koyama and Y. S. Hor and V. D. Kiryukhin and S. Cheong, "Formation of Isomorphic Ir³⁺ and Ir⁴⁺ Octamers and Spin Dimerization in the Spinel CuIr₂S₄," Nature, vol. 416, no. 6877, pp. 155 - 158, Nature Publishing Group, Mar 2002.

The definitive version is available at https://doi.org/10.1038/416155a

Department(s)

Physics

Keywords and Phrases

Cooling; Crystallography; Electric Conductivity; Magnetic Moments; Magnetite; Spinel Structures; Dimerization; Copper; Iridium; Metal Complex; Sulfur; Cation; Crystal Structure; Inorganic Compound

International Standard Serial Number (ISSN)

0028-0836

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2002 Nature Publishing Group, All rights reserved.

Publication Date

01 Mar 2002