Universität zu Köln

Streltsov, Sergey V. and Khomskii, Daniel I. (2016). Covalent bonds against magnetism in transition metal compounds. Proc. Natl. Acad. Sci. U. S. A., 113 (38). S. 10491 - 10497. WASHINGTON: NATL ACAD SCIENCES. ISSN 0027-8424

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Abstract

Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an exclusion of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb2O2F3 and Ba5AlIr2O11, but can also be operative in 3d transition metal oxides, e.g., in CrO2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Streltsov, Sergey V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Khomskii, Daniel I. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-262200
DOI:	10.1073/pnas.1606367113
Journal or Publication Title:	Proc. Natl. Acad. Sci. U. S. A.
Volume:	113
Number:	38
Page Range:	S. 10491 - 10497
Date:	2016
Publisher:	NATL ACAD SCIENCES
Place of Publication:	WASHINGTON
ISSN:	0027-8424
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language DOUBLE EXCHANGE Multiple languages Multidisciplinary Sciences Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/26220