Static magnetic order in metallic K0.49CoO2.
By means of muon-spin spectroscopy, we have found that K0.49CoO2 crystals undergo successive magnetic transitions from a high-T paramagnetic state to a magnetic ordered state below 60 K and then to a second ordered state below 16 K, even though K0.49CoO2 is metallic at least down to 4 K. An isotropic magnetic behavior and wide internal-field distributions suggest the formation of a commensurate helical spin density wave (SDW) state below 16 K, while a linear SDW state is likely to exist above 16 K. It was also found that exhibits a further transition at 150 K presumably due to a change in the spin state of the Co ions. Since the dependence of the internal-field below 60 K was similar to that for Na0.5CoO2, this suggests that magnetic order is more strongly affected by the Co valence than by the interlayer distance or interaction and/or the charge ordering.
Sugiyama
J
J
Toyota Central Research and Development Labs, Inc., Nagakute, Aichi 480-1192, Japan. e0589@mosk.tytlabs.co.jp
Nozaki
H
H
Ikedo
Y
Y
Mukai
K
K
Brewer
J H
JH
Ansaldo
E J
EJ
Morris
G D
GD
Andreica
D
D
Amato
A
A
Fujii
T
T
Asamitsu
A
A