Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 13: Correlated Electrons: Low-dimensional Systems - Materials 1

TT 13.11: Talk

Tuesday, February 26, 2008, 12:15–12:30, H 2053

New natural spin-1/2 kagomé systems — kapellasite Cu₃Zn(OH)₆Cl₂ and haydeeite Cu₃Mg(OH)₆Cl₂ — •Oleg Janson and Helge Rosner — Max Planck Institute for Chemical Physics of Solids, Nöthnitzer str. 40, 01187 Dresden

New natural spin-1/2 systems with kagomé layers — kapellasite Cu₃Zn(OH)₆Cl₂ and haydeeite Cu₃Mg(OH)₆Cl₂ — are studied by full potential density functional calculations using the fplo6.00-24 code. The band structure, obtained by a paramagnetic calculation, was used to solve a tight-binding model. The transfer integrals were mapped subsequently to a Hubbard model and to a Heisenberg model, giving an estimate for the antiferromagnetic (AF) exchange. The total exchange, containing AF and ferromagnetic (FM) parts, was derived from LSDA + U supercell calculations. As the main result, we find that in both compounds only two exchange integrals are relevant: the nearest neighbour exchange J₁ and the interaction J_d along the diagonals of the Cu²⁺ hexagons. Surprisingly, the size of these integrals depends strongly on the O—H bond length which was therefor optimized with respect to the total energy, resulting in about 1 Å for both compounds. Using the optimized O—H bond length, we find J₁>J_d in kapellasite and J₁∼J_d in haydeeite. According to our results, kapellasite can be described as a modified kagomé lattice, while interpenetrating chains should be considered for haydeeite. Our results should encourage new experimental studies of these interesting materials.