Drechsler S-L, Volkova O, Vasiliev A N, Tristan N, Richter J, Schmitt M, Rosner H, Málek J, Klingeler R, Zvyagin A A, Büchner B
Leibniz-Institut für Festkörper-und Werkstoffforschung (IFW) Dresden, P.O. Box 270116, D-01171 Dresden, Germany.
Phys Rev Lett. 2007 Feb 16;98(7):077202. doi: 10.1103/PhysRevLett.98.077202. Epub 2007 Feb 12.
From thermodynamics, local spin density approximation+Hubbard U studies and exact diagonalizations of a five-band Hubbard model on CuO2 stripes we find that Li2ZrCuO4 (Li2CuZrO4 in traditional notation) is close to a ferromagnetic critical point. Analyzing its susceptibility chi(T) and specific heat cp(T,H) within a Heisenberg model, we show that the ratio of the 2nd to the 1st neighbor exchange integrals alpha=-J2/J1 approximately 0.3 is close to the critical value alphac=1/4. Comparing with related chain cuprates we explain the rather strong field dependence of cp, the monotonic downshift of the peak of chi(T), and its increase for alpha-->alphac+0.
