  The magnetic lattice of mixed-valence Mn ions in
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ is selectively diluted by partial substitution of
Al or Ti for Mn. The ferromagnetic transition temperature $T_\mathrm{c}$ and
the saturation magnetization $M_\mathrm{s}$ both decrease with substitution. By
presenting the data in terms of selective dilution, $T_\mathrm{c}$ in the
low-doping region is found to follow the relation
$T_\mathrm{c}=T_\mathrm{c0}(1-n_\mathrm{p})$, where $T_\mathrm{c0}$ refers to
the undiluted system and $n_\mathrm{p}$ is the dilution concentration defined
as $n_\mathrm{p}=x/0.7$ or $n_\mathrm{p}=x/0.3$ for $M^\prime=$ Al or Ti,
respectively. The scaling behavior of $T_\mathrm{c}(n_\mathrm{p})$ can be
analyzed in the framework of the molecular-field theory and still valid when Mn
is substituted by both Al and Ti. The results are discussed with respect to the
contributions from ferromagnetic double exchange and other possible
antiferromagnetic superexchange interactions coexisting in the material.
