Cooperative Jahn-Teller distortion leading to the spin-1/2 uniform antiferromagnetic chains in triclinic perovskites AgCuF3 and NaCuF3

Polycrystalline samples of AgCuF3, isostructural with NaCuF3, were synthesized by solid state reaction and characterized by powder X-ray diffraction. The magnetic properties of AgCuF3 and NaCuF3 were examined by measuring their magnetic susceptibilities and evaluating their spin exchange interactions. The three-dimensional CuF3 network of corner-sharing CuF6 octahedra present in AgCuF3 and NaCuF3 shows a cooperative Jahn-Teller distortion such that their magnetic susceptibilities above 50 K are well described by an S = 1/2 Heisenberg uniform antiferromagnetic chain model with average spin exchange of J/k(B) similar or equal to -300 and -180 K. respectively. The relative strengths of these interactions are well reproduced by spin dimer analysis based on tight-binding calculations, but not by mapping analysis based on first principles density functional calculations. (C) 2009 Elsevier Masson SAS. All rights reserved.