物理化学学报 >> 2010, Vol. 26 >> Issue (03): 769-774.doi: 10.3866/PKU.WHXB20100242

量子化学及计算化学 上一篇    下一篇

三角晶格反铁磁CuFeO2的磁性和电子结构

仲崇贵, 蒋青, 董正超, 方靖淮, 曹海霞   

  1. 苏州大学物理科学与技术学院, 江苏 苏州 215006; 南通大学理学院, 江苏 南通 226007
  • 收稿日期:2009-10-13 修回日期:2009-12-20 发布日期:2010-03-03
  • 通讯作者: 蒋青 E-mail:qjiang@suda.edu.cn; chgzhong@ntu.edu.cn

Magnetism and Electronic Structures of Triangular Lattice Antiferromagnetic CuFeO2

ZHONG Chong-Gui, JIANG Qing, DONG Zheng-Chao, FANG Jing-Huai, CAO Hai-Xia   

  1. School of Physical Sciences and Technology, Suzhou University, Suzhou 215006, Jiangsu Province, P. R. China; School of Science, Nantong University, Nantong 226007, Jiangsu Province, P. R. China
  • Received:2009-10-13 Revised:2009-12-20 Published:2010-03-03
  • Contact: JIANG Qing E-mail:qjiang@suda.edu.cn; chgzhong@ntu.edu.cn

摘要:

基于广义梯度近似(GGA)的密度泛函理论(DFT), 通过构造铁磁(FM), 阻挫的三角非共线反铁磁(FAFM)、上上下下型共线反铁磁(↑↑↓↓AFM)三种不同磁性构型, 从非共线磁性结构计算出发, 优化了低温铜铁矿CuFeO2晶体材料的几何结构, 研究了磁性结构对电子结构、能隙和磁矩等的作用. 计算发现上上下下型反铁磁自旋排列能促进能隙形成, 总能降低, 磁矩增大. 由于上上下下型反铁磁与阻挫三角非共线反铁磁相能量接近, 外场的作用容易导致磁性结构相变到阻挫的三角反铁磁态, 其电子态密度分布与X光发射光谱测得的结果一致, 即具有高自旋的Fe离子3d电子自旋向上的子带中心位于Cu 3d能态之下, O 2p能态以上, 而且配位场理论分析表明Fe离子3d态自旋向下的空轨道为铁电极化提供了有利的化学环境.

关键词: 铁磁, 反铁磁, 阻挫, 磁电, 杂化, 配位场

Abstract:

Based on a non-collinear magnetic structure calculation, the magnetism, energy gap, and electronic structures of the triangular lattice antiferromagnetic delafossite CuFeO2 were investigated by density functional theory (DFT) within the generalized gradient approximation (GGA) approach. By producing three types of magnetic configurations including ferromagnetic (FM), frustrated triangular non-collinear antiferromagnetic (FAFM), and up-up-down-down collinear antiferromagnetic (↑↑↓↓AFM) ordering, a full optimization of the lattice parameters and internal coordinates was performed for the low temperature hexagonal structure. The calculations show that the up-up-down-down spin arrangement plays an important role in the formation of the band gap, the decrease in total energy and the increase in magnetic moment. Since a small difference exists between the total energy of the FAFMand ↑↑↓↓AFM phase, the ↑↑↓↓AFMeasily undergoes a phase transition to the FAFMstate when an external magnetic field is applied. Additionally, the electronic densities of states (DOS) in the ↑↑↓↓AFMphase qualitatively agrees with the results of X-ray emission spectra, that is, the Fe ion is in a high-spin state with the spectral weight of the Fe 3d spin-up band centered slightly below the Cu 3d but above the O 2p bands. Analysis with ligand field theory also indicates that the empty orbital of the Fe 3d spin-down provides a chemical environment favorable for ferroelectric polarization.

Key words: Ferromagnet, Antiferromaget, Frustration, Magnetoelectricity, Hybridization, Ligand field

MSC2000: 

  • O641.4