Ab initio study of magnetic interactions in KCuF3 and K2CuF4 low-dimensional systems

[摘要] The ab initio cluster model approach has been used to study the electronic structure and magnetic coupling of KCuF3 and K2CuF4 ill their various ordered polytype crystal forms. Due to a cooperative Jahn-Teller distortion these systems exhibit strong anisotropies. In particular, the magnetic properties strongly differ from those of isomorphic compounds. Hence, KCuF3 is a quasi-one-dimensional (1D) nearest neighbor Heisenberg antiferromagnet whereas K2CuF4 is the only ferromagnet among the K2MF4 series of compounds (M = Mn, Fe, Co, Ni, and Cu behaving all as quasi-2D nearest neighbor Heisenberg systems. Different ab initio techniques are used to explore the magnetic coupling in these systems. All methods, including unrestricted Hartree-Fock, are able to explain the magnetic ordering. However, quantitative agreement with experiment is reached only when using a state-of-the-art configuration interaction approach. Finally, an analysis of the dependence of the magnetic coupling constant with respect to distortion parameters is presented. [S0163-1829(99)09831-8].

[关键词] DENSITY-FUNCTIONAL THEORY;ELECTRONIC-STRUCTURE CALCULATIONS;TRANSITION-METAL COMPOUNDS;CLUSTER MODEL-CALCULATIONS;IONIC SOLIDS;2-DIMENSIONAL FERROMAGNET;NEUTRON-SCATTERING;EXCHANGE;LA2CUO4;KNIF3