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

• 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
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640358/
• 关键词: layered oxysulflde; metal-nonmetal transition; X-ray photoemission spectroscopy; Strongly correlated electron; two-dimensional antiferromagnet; 高温超伝導関連物質; CoO_2平面; フラストレーション; 2次元反強磁性相関; スピンの揺らぎ; スピングラス; 高温超伝導体関連物質

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.

新型层状过渡金属氧硫化物Sr_2Cu_2CoO_2S_2（1/4 mmm）晶体具有一种特殊的共生结构，由正方形平面CoO_2片层和SrCu_2S_2层交替组成，Sr_2Cu_2CoO_2S_2是一种p型反铁磁半导体材料，其TN（= 200 K）由磁化率（χ）决定。中子粉末衍射（NPD）测量。在T_t（= 140 K）以上，X显示了一个宽的最大值，表明二维（2D）AF性质，如通常在K_2NiF_2<4->型AF化合物中所见。渗透率导数（dμ/dT）曲线在T_t附近出现拐点，此时AF性质由二维转变为三维，T_t随压力（dT）的增加而急剧上升。dP-13.5K/kbar），表明3D型AF状态在压力下比2D型AF状态更稳定。dFL /dT曲线中的T_t对应于电阻率的弯曲点，T_t以上出现最近邻跳跃导电。Cu_2S_2层中的Cu离子处于一价态（Cu_+：d_<10>），CoO_2层具有强相关的电子性质（O 2 p到Co 3d的电荷转移能Δ=4.2eV，在位d-d库仑）。排斥能U=5eV），根据实验和理论X射线光电子能谱（XPS）研究。因此，磁性不是来自于Cu_2S_2层，而是来自于强关联的CoO_2方晶面，这与NPD分析相一致。在Cu掺杂的Sr_2Cu_2CoO_2S_2和Co_Cu_xxO_2中<1-x>，x&lt;0.4的样品表现为半导体性质，而x=0.4和x=0.5的样品分别在200 K和175 K表现为金属-半导体转变。Cu掺杂到CoO_2面的这一特征表明Sr_2Cu_2（Co，Cu）O_2S_2位于Zaanen-Sawatzky-艾伦电子图中的强关联金属区附近。

项目成果

M.Matoba, T.Takeuchi, Y.Kamihara, M.Itoh, K.Ohoyama, and Y.Yamaguchi: "Magnetism of Novel Layered Cobalt Oxysulfide Sr_2Cu_2CoO_2S_2 With Strongly Correlated CoO_2 Square-Planes"Physica B. (in press).

M.Matoba、T.Takeuchi、Y.Kamihara、M.Itoh、K.Ohoyama 和 Y.Yamaguchi：“具有强相关 CoO_2 方形平面的新型层状氧硫化钴 Sr_2Cu_2CoO_2S_2 的磁性”Physica B.（出版中）。

M.Matoba et al.: "Neutron Powder Diffraction on Novel Layered Cobalt Oxysulfide Sr_2Cu_2CoO_2S_2 in Strongly Correlated Electron Systems"J.Phys.Soc.Jpn. 70(Suppl). 64-66 (2001)

M.Matoba 等：“强相关电子系统中新型层状氧硫化钴 Sr_2Cu_2CoO_2S_2 的中子粉末衍射”J.Phys.Soc.Jpn。

S.Okada, M.Matoba, H.Yoshida, K.Ohoyama, and Y.Yamaguchi: "Pressure Effect on Magnetic and Electronic Nature of Sr_2Cu_2CoO_2S_2 with Strongly Correlated CoO_2 Square-Planes"J.Phys. Chem. Solids. (in press).

S.Okada、M.Matoba、H.Yoshida、K.Ohoyama 和 Y.Yamaguchi：“压力对具有强相关 CoO_2 方形平面的 Sr_2Cu_2CoO_2S_2 的磁和电子性质的影响”J.Phys。

S.Okada,M.Matoba et al.: "Pressure Effect on Magnetic and Electronic Nature of Sr_2Cu_2CoO_2S_2 with Strongly Correlated CoO_2 Square-Planes."J.Phys.Chem.Solids. (in press).

S.Okada,M.Matoba 等人：“压力对具有强相关 CoO_2 方形平面的 Sr_2Cu_2CoO_2S_2 的磁性和电子性质的影响。”J.Phys.Chem.Solids。

Y.Kamihara, S, Okada and M.Matoba: "Properties of Layered Magnetic Semiconducors Sr_2Cu_2Zn_<1-x>Mn_xO_2S_2 in Multinary Systems [in Japanese]."J.Magn. Soc. Jpn.. 25. 739 (2001)

Y.Kamihara、S、Okada 和 M.Matoba：“多元系统中层状磁半导体 Sr_2Cu_2Zn_<1-x>Mn_xO_2S_2 的特性 [日语]”。