Effects of selective dilution on the magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)

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 $T_{\mathrm{c}}=T_{\mathrm{c}0}(1-n_{\mathrm{p}})$, where $T_{\mathrm{c}0}$ refers to the undiluted system and $n_{\mathrm{p}}$ is the dilution concentration defined as $n_{\mathrm{p}}=x\mathrm{/}0.7$ or $n_{\mathrm{p}}=x\mathrm{/}0.3$ for $M^{\mathrm{\prime }}=$ 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.