Dynamic Spin Properties of La_1.98Sr_0.02CuO₄

Neutron scattering experiments have been performed to study the dynamic spin properties of La _1.98 Sr _0.02 CuO ₄ , a crystal with just enough Sr to destroy three-dimensional long range magnetic order and induce spin-glass behavior at low temperatures. The q -integrated susceptibility \(\int \,{\rm d}^{2}q_{\rm 2D}\,{\rm Im}\,\chi _{\rm 2D}(q_{\rm 2D},\,\omega )\) follows the scaling function of ω/ T suggested by Keimer et al. Below 3 meV, however, clear deviation from the scaling function is observed at low temperatures. This probably originates from a gap in the spin-wave-like excitations due to the out-of-plane anisotropy.