Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates
Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates
复制标题
DOI：
10.1103/physrevb.78.155116
复制
发表时间：
2008-07
影响因子：
3.7
通讯作者：
G. Lang;J. Bobroff;H. Alloul;G. Collin;N. Blanchard
中科院分区：
文献类型：
--
作者：
G. Lang;J. Bobroff;H. Alloul;G. Collin;N. Blanchard
保利政权到高x居里魏斯政权。对于0.5x0.62，磁化率随温度变化的最大值T的存在表明存在依赖于x的能量标度。T1弛豫测量确定了xx自旋关联的主要反铁磁性特征。这与通常假定的在此x范围内不相关的Pauli行为相矛盾，并且与所观察到的xx的铁磁关联不一致。从59Co核磁共振数据可以看出，当x远离x=0.5时，随着x的增大，非磁性Co3+格位逐渐出现，打破了x=0.5时Co态的均匀性。核磁共振检测到的59 Co四极效应的主要特征，以及粉末X射线衍射数据的迹象，使我们勾勒出Co3+位的可能结构来源。根据这一系列实验观测，提出了一个考虑关联及其与x的依赖关系的系统存在的相图。
Pauli-like regime to the high-x Curie-Weiss regime. For 0.5x 0.62, the presence of a maximum T in the temperature dependence of the susceptibility shows the existence of an x-dependent energy scale. T1 relaxation measurements establish the predominantly antiferromagnetic character of spin correlations for xx. This contradicts the commonly assumed uncorrelated Pauli behavior in this x range and is at odds with the observed ferromagnetic correlations for xx. It is suggested that at a given x the ferromagnetic correlations might dominate the antiferromagnetic ones above T. From 59 Co NMR data, it is shown that moving toward higher x away from x = 0.5 results in the progressive appearance of nonmagnetic Co 3+ sites, breaking the homogeneity of Co states encountered for x 0.5. The main features of the NMR-detected 59 Co quadrupolar effects, together with indications from the powder x-ray diffraction data, lead us to sketch a possible structural origin for the Co 3+ sites. In light of this ensemble of experimental observations, a phase diagram taking into account the systematic presence of correlations and their x dependence is proposed.