Magnetic Correlations In Ybaco4o7 On Kagome And Triangular Lattices

Magnetic correlation in YBaCo4O7 with kagome and triangular lattices was studied through inelastic-neutron-scattering measurements on a single crystal sample. The broad magnetic excitation was observed below 45 meV and showed dispersions both within the c plane and along the c axis. The wave vector with the minimum energy of the magnetic excitation was totally different from the magnetic Bragg point. Our analysis with the first-moment-sum rule suggests that Co ions in YBaCo4O7 form a unique three-dimensional network with the geometrically frustration.