Evolution of ferromagnetism and electron correlation in Eu1−xGdxTiO3 thin films with 4f7 configuration

We have studied magnetic and transport properties of compressively strained ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{Gd}}_x\mathrm{Ti}{\mathrm{O}}₃$ (EGTO) thin films up to a high doping level, $x=0.55$, grown by gas-source molecular beam epitaxy. In comparison with a nonmagnetic dopant $({\mathrm{La}}³⁺)$ in ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{La}}_x\mathrm{Ti}{\mathrm{O}}₃$ (ELTO), ${\mathrm{Gd}}³⁺$ has the same $4{f}⁷$ moment as ${\mathrm{Eu}}²⁺$, but a smaller ionic radius to induce buckling of the $\mathrm{Ti}{\mathrm{O}}₆$ octahedra and hence reduces the one-electron bandwidth. The evolution of ferromagnetism and electron correlation is more clearly observed in EGTO thin films in the filling $(x)$ dependence of Curie temperature and the coefficient of temperature-squared resistivity. The systematic comparison of the magnetic phase diagrams for EGTO and ELTO has revealed significant differences caused by the presence (absence) of a magnetic moment in ${\mathrm{Gd}}³⁺\phantom{\rule{4pt}{0ex}}({\mathrm{La}}³⁺)$ and an effect due to the difference in electron correlation strength.