https://doi.org/10.1140/epjb/e2002-00407-3
Phase evolution of layered cobalt oxides versus varying corrugation of the cobalt-oxygen basal plane
Max-Planck-Institut für Physik komplexer Systeme,
Nöthnitzer Str. 38, 01187 Dresden, Germany
Corresponding author: a wu@fhi-berlin.mpg.de
Received:
28
July
2002
Revised:
10
October
2002
Published online:
31
December
2002
A general spin-state model and a qualitative physical
picture
have been proposed for
a class of lately synthesized layered cobalt oxides
(LCOs) by means of density functional calculations.
As the plane corrugation of the cobalt-oxygen layer
decreases,
the LCOs evolve from
a high-spin (HS) superexchange-coupled antiferromagnetic (AFM)
insulator to
an almost-HS AFM/ferromagnetic (FM) competing
system where the FM coupling is mediated via the p-d
exchange by an increasing
amount of delocalized holes having mainly the
planar O 2p character.
It is tentatively suggested
that the delocalized holes more
than 0.3 per CoO2 basal square are likely necessary for the
insulator-metal and/or AFM-FM transitions in the
corrugation-weakened LCOs.
A phase control may be realized in LCOs by varying the plane
corrugation (thus modifying the hole concentration) through an
ionic-size change of the neighboring layers
on both sides of the cobalt-oxygen layer. In addition, a few
experiments are suggested for a check of the present model and
picture.
PACS: 71.27.+a – Strongly correlated electron systems; heavy fermions / 71.20.-b – Electron density of states and band structure of crystalline solids / 75.10.-b – General theory and models of magnetic ordering
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002