  On the basis of the picture of a quasi-one-dimensional (q-1d) Fermi surface
(FS), recently proposed by authors for LSCO systems, spin excitation spectrum,
Im chi(q,omega), is calculated in the 'RPA' within the slave-boson mean-field
approximation to the t-J model. It is found that Im chi(q,omega) shows both
incommensurate (IC) and diagonal IC (DIC) peaks, whose realization does not
depend on the existence of the d-wave gap. The peak positions do not change
appreciably with omega and the sharp peaks survive down to the low hole doping
rate. The d-wave gap suppresses both the IC peak and the DIC peak, but the
degree of suppression as a function of omega is different between them. Taking
these results together with results for the two-dimensional FS, we argue that
essential features of magnetic excitation in LSCO systems can be understood in
terms of the q-1d picture of the FS.
