An NSF Materials Research Science and Engineering Center (MRSEC)

1. Center for Emergent Materials The Ohio State University http://cem.osu.edu Understanding magnetism in a high temperature magnetic semiconductor J1 Modeling the magnetic properties of both insulating and metallic double perovskites Ferrimagnetism in double perovskites such as Sr2FeMoO6 is thought to be closely linked to delocalization of the minority spin electrons. Therefore, it is surprising that Sr2CrOsO6, a semiconductor with localized electrons, has the highest magnetic ordering temperature of all double perovskites (TC = 720 K). This is one of many observations that illustrate shortcomings in our understanding of magnetism across the entire double perovskite family. To address this need we have recently developed a single unifying framework that can be applied to all double perovskites, metallic or insulating. The decoupling of metallic conductivity and magnetism in Sr2CrOsO6 results from the Coulomb U on Os which leads to Mott insulating behavior. Thus superexchange interactions drive the high TC. Other intriguing behaviors can also be explained. For example, why is there a net moment at all given that both Cr and Os are d3 ions,and naively one would expect their moments to cancel? Why does the magnetization show such an unusual temperature dependence (see figure inset). Both features are due to frustration arising from competition between antiferromagnetic Cr−Os (J1) and Os−Os (J2) superexchange interactions. Finally we note that unlike Sr2 CrReO6, spin-orbit coupling is completely quenched and has no qualitative effects on the properties. Top: Theoretical magneti-zation M(T) of Sr2CrOsO6 (blue); inset: experimental data (red). Left: The Os−Cr (J1) and Os−Os (J2) interactions. The blue, red and green spheres represent Os, O and Cr respectively (Sr not shown for clarity) J2 Mohit Randeria, Nandini Trivedi, Onur Erten, O.N. Meetei, Anamitra Mukherjee, & Patrick Woodward Co Au Co An NSF Materials Research Science and Engineering Center (MRSEC) Chris P. Hammel, Ohio State University Research Foundation, DMR 0820414