Sugiyama J, Nozaki H, Ikedo Y, Mukai K, Brewer J H, Ansaldo E J, Morris G D, Andreica D, Amato A, Fujii T, Asamitsu A
Toyota Central Research and Development Labs, Inc., Nagakute, Aichi 480-1192, Japan.
Phys Rev Lett. 2006 Jan 27;96(3):037206. doi: 10.1103/PhysRevLett.96.037206.
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.
通过μ子自旋光谱法，我们发现K0.49CoO2晶体经历了一系列磁转变，从高温顺磁态转变为60K以下的磁有序态，然后在16K以下转变为第二有序态，尽管K0.49CoO2至少在4K以下是金属性的。各向同性的磁行为和宽的内场分布表明在16K以下形成了相称的螺旋自旋密度波（SDW）态，而在16K以上可能存在线性SDW态。还发现它在150K处表现出进一步的转变，这可能是由于Co离子自旋态的变化。由于60K以下内场的依赖性与Na0.5CoO2的相似，这表明磁有序受Co价态的影响比层间距离或相互作用和/或电荷有序更强。
