An overall energy spectrum of magnetic fluctuations in the superconducting la_l.85 Sr_0.15CuO₄

High-energy pulsed neutron inelastic scattering experiments have been performed using single crystals of La_1.85 Sr_0.15 CuO ₄ to study magnetic fluctuations in the superconducting phase. A peak centered at the reciprocal point (π, π ) is well defined below around 120 meV and rapidly damped beyond this energy. However, the "background- subtracted" scattering intensities indicate that magnetic signals remain up to around 300 meV. These data combined with the results obtained by triple-axis neutron scattering experiments provide the first overall energy spectrum of the dynamical susceptibility in La_1.85 Sr_0.15 CuO ₄. The obtained spectrum is much wider than that of YBa ₂Cu₃O_7-d(d∼0).