Polarized and unpolarized neutron-scattering study of the dynamical spin susceptibility of YBa2Cu3O7.

We report an extensive study of magnetic excitations in fully oxygenated YBa2Cu3O7 , using neutron scattering with and without spin polarization analysis. By calibrating the measured magnetic intensity against calculated structure factors of optical phonons and against antiferromagnetic spin waves measured in the same crystal after deoxygenation to YBa2Cu3O6.2, we establish an absolute intensity scale for the dynamical spin susceptibility, x9~q,v!. The integrated spectral weight of the sharp magnetic resonance at \v540 meV and qi5(p/a ,p/a) in the superconducting state is *d(\v)x res 9 (q,v)5(0.5260.1) at low temperatures. The energy and spectral weight of the resonance are measured up to T50.8Tc . The resonance disappears in the normal state, and a conservative upper limit of 30 states/eV is established for the normal state dynamical susceptibility at qi5(p/a ,p/a) and 10 meV<\v<40 meV. Our results are compared to previous neutronscattering data on YBa2Cu3O7 , theoretical interpretations of NMR data and current models of the 40 meV resonance. @S0163-1829~96!03133-5#