Spin-1/2 Heisenberg antiferromagnetic chains in the frustrated spinel lattice of GeCu2O4

One-dimensional quantum antiferromagnetism has been found in a tetragonal s pinel oxide, GeCu2O4. Actually the temperature dependence of magnetic susce ptibility exhibiting a broad maximum around 80 K can be well-described as t hat of S = 1/2 Heisenberg antiferromagnetic chains with J/k(B) = 135 K. Coo peration of spin frustration caused by the triangular arrangement of the cu pric ions at octahedral sites and the Jahn-Teller elongation of the CuO6 oc tahedra along the c axis seems to lead to the formation of magnetically iso lated CuO2 chains made of edge-sharing CuO4 squares. However, a small drop in susceptibility and also a sharp spike in specific heat suggesting the oc currence of long-range antiferromagnetic ordering are observed at 33 K. The effects of Si-for-Ge substitution and Mg-for-Cu substitution are also repo rted.