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First principles electronic structure calculations reveal certain
important common features in the conduction band polarization of many of
the newly examined colossal magnetoresistance (CMR) materials. Most CMR
compounds seem to possess a localized, magnetic band slightly below the
Fermi energy. This localized band transfers polarization to a relatively
broad conduction band. The nature of the two bands in different systems
can be quite distinct. In the perovskite-derived manganese oxides, the
magnetic band is derived from Mn t(2g) states while the conduction band
is derived from Mn e(g) states. In the chalcospinel Fe0.5Cu0.5Cr2S4 the
Cr t(2g) states which are below E-F polarize conducting Fe d states. In
Gd metal and the newly discovered CMR material GdI2, the metallic Gd d
states are polarized by the underlying f levels. In double perovskites
(elpasolites) such as Sr2FeMoO6, Fe states similarly polarize the
broader Mo-derived conducting d states. In the pyrochlore Tl2Mn2O7,
localized, magnetic Mn d states polarize the conduction band derived
from bonding Tl-O states. In all the systems except Gd metal, the
conduction band seems to be strongly spin differentiated. The
systematics obtained here provide guidelines for the design of new CMR
systems. (C) 2000 Elsevier;Science Ltd. All rights reserved.
