Transport properties, magnetic ordering, and hyperfine interactions in Fe-dopedLa0.75Ca0.25MnO3: Localization-delocalization transition

Transport properties of ${\mathrm{La}}_{0.75}{\mathrm{Ca}}_{0.25}{\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x{\mathrm{O}}_{3+y}$ ceramics are examined for “$x$” values from 0 to 0.05. Dramatic changes are observed in the resistivity and its temperature dependence as “$x$” increases above about 0.04. Temperature-dependent Mössbauer spectroscopy and magnetization studies are also performed. These data suggest that transport in this system necessarily involves quasiparticle excitation in association with the double exchange process and it undergoes localization-delocalization-type transition at a critical dopant concentration.