Electrical transport and magnetic properties of a possible electron-doped layered manganese oxide

We report on the structural, transport, and magnetic properties of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{x}$ thin films grown in vacuum by pulsed-laser deposition. The as-grown thin films have both the matrix ${\mathrm{La}}_{1.34}{\mathrm{Sr}}_{0.66}{\mathrm{MnO}}_{4}$ phase with ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ structure and an embedded MnO phase. The electrical transport and magnetic properties of the films are determined mainly by those of the matrix phase. By annealing, the as-grown thin films can be transformed into the normal ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ single phase, which shows the expected colossal magnetoresistance effect. Based on the composition of the matrix phase, and the structural, electrical, and magnetic properties of the films, we propose that the matrix phase is possibly electron doped with a mixed valence of ${\mathrm{Mn}}^{2+}{/\mathrm{M}\mathrm{n}}^{3+}$ instead of the ${\mathrm{Mn}}^{3+}{/\mathrm{M}\mathrm{n}}^{4+}$ as in the hole-doped case.