Transcript Ohio State MRSEC 0820414 Patrick Woodward Understanding

Center for Emergent Materials
The Ohio State University
http://cem.osu.edu
Understanding magnetism in a high temperature magnetic semiconductor
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.
Mohit Randeria, Nandini Trivedi, Onur Erten, O.N. Meetei, Anamitra
CoMukherjee,
Au & Co
Patrick Woodward
J1
J2
Top: Theoretical magnetization 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)
An NSF Materials Research Science and Engineering Center (MRSEC)
Supported under Award Number DMR-0820414