An NSF Materials Research Science and Engineering Center (MRSEC)

An NSF Materials Research Science and Engineering Center (MRSEC)Supported under Award Number DMR-0820414

A new paradigm for magnetism in complex metal oxides

Center for Emergent MaterialsThe Ohio State University

Co Au Co

Chris P. Hammel, Ohio State University Research Foundation, DMR 0820414

http://cem.osu.edu

J3−38 meV

The magnetic structure of Sr2CoOsO6. The osmium (in red) and cobalt spins (in blue) order independently. This unusual behavior results from the fact that the magnetic interactions between nearest neighbors, Os-O-Co (J1), are an order of magnitude weaker than the longer Os-O-Co-O-Os (J2) and Co-O-Os-O-Co (J3) interactions. Note, positive and negative values of J indicate parallel and antiparallel coupling of spins, respectively.

Magnetism in insulating oxides is governed by superexchange interactions, whereby the electron spin on one transition metal ion is coupled to the spin on neighboring ions through the intervening oxide ions. In most cases, the direction (parallel or antiparallel) and approximate strength of these interactions can be predicted using the rules developed by Goodenough and Kanamori in the 1950’s. In the double perovskite Sr2CoOsO6, the osmium and cobalt ions independently order at different temperatures, 107 K and 68 K, respectively. This behavior implies that long range interactions between ions of the same type are stronger than much shorter range interactions between different ions. DFT calculations confirm this hypothesis: |J1| < |J2| |J3|. This work highlights the need for rules that can be used to predict magnetism in compounds containing both light (e.g. Co) and heavy (e.g. Os) transition metal ions.Morrow, Woodward, Mishra, Windl (unpublished)

J1−4.4 meV

J2+43 meV