Magnon dispersion curve of antiferromagnetic Bi2CuO4.

Abstract

We present detailed neutron-scattering studies of the magnon dispersion curve in ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$. We show the existence of a single doubly degenerate dispersion branch. In this antiferromagnetic S=1/2 system, we found that our experimental results are totally accounted for by a model of four superexchange interactions: ${\mathit{J}}_{1}$=2.2\ifmmode\pm\else\textpm\fi{}0.15; ${\mathit{J}}_{2}$=0.7\ifmmode\pm\else\textpm\fi{}0.05; ${\mathit{J}}_{3}$=0.2\ifmmode\pm\else\textpm\fi{}0.05; ${\mathit{J}}_{4}$=0.8\ifmmode\pm\else\textpm\fi{}0.05; and anisotropy constant D=0.3\ifmmode\pm\else\textpm\fi{}0.05 in meV. These Cu-Cu interactions are similar to those between the two ${\mathrm{CuO}}_{2}$ planes of the so-called bilayer of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$, and this work is a direct determination of such couplings in copper oxides.