  We report a study of magnetic, thermal, and transport properties of La(3+)
substituted Sr2RuO4, performed in order to investigate the effects of
additional electron doping in this correlated metal. A gradual enhancement of
the electronic part of specific heat and a more drastic increase of the static
magnetic susceptibility were observed in Sr(2-y)La(y)RuO(4) with increasing y.
Furthermore, the quasi-two-dimensional Fermi-liquid behavior seen in pure
Sr2RuO4 breaks down near the critical concentration y ~ 0.20. Combined with a
realistic tight-binding model with rigid-band shift of Fermi level, the
enhancement of the density of states can be ascribed to the elevation of the
Fermi energy toward a van Hove singularity of the thermodynamically dominant
\gamma Fermi-surface sheet. On approaching the van Hove singularity, the
effective nesting-vector of the \gamma band shrinks and further enhances the
susceptibility near the wave vector q ~ 0. We attribute the non-Fermi-liquid
behavior to two-dimensional ferromagnetic fluctuations with short range
correlations at the van Hove singularity. The observed behavior is in sharp
contrast to that of Ti(4+) substitution in Sr2RuO4 which enhances
antiferromagnetic fluctuations and subsequently induces incommensurate magnetic
ordering associated with the nesting between the other Fermi-surface sheets
(\alpha and \beta). We thus establish that substitution of appropriate chemical
dopants can band-selectively modify the spin-fluctuation spectrum in the
spin-triplet superconductor Sr2RuO4.
