Magnetic and electronic nature of layered transition-metal oxysulfides

层状过渡金属硫氧化物的磁性和电子性质

基本信息

批准号：
11640358
负责人：
MATOBA Masanori
金额：
$ 2.3万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Novel layered transition-metal oxysulfide Sr_2Cu_2CoO_2S_2 (I/4mmm), which crystallizes in an unusual intergrowth structure with alternating square-planar CoO_2 sheets and SrCu_2S_2 layers, have been studied to reveal the electronic and magnetic nature as follows.Sr_2Cu_2CoO_2S_2 is a p-type antiferromagnetic (AF) semiconductor with TN (=200K) determined by the magnetic susceptibility (χ) ana the neutron powder diffraction (NPD) measurements. Above T_t (=140K), the. χ shows a broad maximum indicative of two-dimensional (2D) AF nature as normally seen for K_2NiF_<4->type AF compounds. The derivative permeability (dμ/dT) curves have a kink near T_t at which the AF nature is changed from 2D to 3D ; T_t extremely rises with increasing pressure (dT./dP-13.5K/kbar), indicating that 3D-type AF state is more stable under pressure as compared to 2D-type AF state. Tlle T_t in the dFL /dT curves correspond to the bending point of the resistivity, and above T_t the nearest-neighbor hopping conduction occurs. The Cu ion of die Cu_2S_2 layer is in the mono-valent state (Cu_+ : d_<10>) and the CoO_2 square-planes have the strongly correlated electronic nature (with the O 2p-to-Co 3d charge transfer energy Δ=4.2eV and the on-site d-d Coulomb. repulsion energy U=5eV), according to experimental and theoretical x-ray photoemission spectroscopy (XPS) study. Therefore, the magnetic nature is not originated from the Cu_2S_2 layers but the strongly correlated CoO_2 square-planes, which is consistent with the NPD analysis. In Cu-doped Sr_2Cu_2CoO_2S_2 with Co_<1-x>Cu_xxO2 Planes, the samples with x<0.4 shows a semiconducting behavior, while the samples with x=0.4 and x=0.5 exhibits a metal-semiconductor transition at 200K and 175K, respectively. This feature of Cu-doping into the CoO_2 planes suggests that Sr_2Cu_2(Co, Cu)O_2S_2 situates near the strongly correlated metallic region in the so-called Zaanen-Sawatzky-Allen electronic diagram.

新型分层过渡金属氧硫化物SR_2CU_2COO_2S_2（I/4MMM），它以与替代方形 - 平面COO_2 sheets和srcu_2s_2层的不寻常的增长结构结晶，以揭示电子和磁性，以揭示电子和磁性iS_ 2sr_2cu_2cu_2cu_2cuo_2cuo ooo。由磁敏感性（χ）和中子粉末衍射（NPD）测量结果确定的TN（= 200K）的抗铁磁（AF）半导体。上方T_T（= 140K），。 χ显示了通常在K_2NIF_ <4->类型的AF化合物的二维（2D）AF性质的广泛指示。衍生渗透性（Dμ/DT）曲线在T_T附近有一个扭结，在T_T中，AF性质从2D更改为3D； T_T随着压力的增加（DT./DP-13.5K/KBAR）极高地升高，表明与2D型AF状态相比，在压力下3D-TYPE AF状态更稳定。 DFL /DT曲线中的T_T对应于电阻的弯曲点，而在T_T上方则发生最近的邻居跳动传导。 The Cu ion of die Cu_2S_2 layer is in the mono-valent state (Cu_+ : d_<10>) and the CoO_2 square-planes have the strongly correlated electronic nature (with the O 2p-to-Co 3d charge transfer energy Δ=4.2eV and the on-site d-d Coulomb. repulsion energy U=5eV), according to experimental and theoretical x-ray photoemission spectroscopy （XPS）研究。因此，磁性不是从CU_2S_2层原始的，而是强相关的COO_2方形平面，这与NPD分析是一致的。在cu掺杂的SR_2CU_2COO_2S_2中，具有Co_ <1-X> Cu_xxo2平面，x <0.4的样品显示了半导体的行为，而x = 0.4和x = 0.5的样品分别在200K和175K处显示了金属 - 巨型导体的转换。 CU掺杂到COO_2平面的此特征表明，在所谓的Zaanen-Sawatzky-Sawatzky-Allen Allen电子图中，SR_2CU_2（CO，CU）O_2S_2位于强相关的金属区域附近。