Polarons and phase separation in lanthanum-based manganese perovskites: A139Laand55MnNMR study

Abstract

Low-temperature ${}^{139}\mathrm{La}$ and ${}^{55}\mathrm{Mn}$ NMR line shape measurements in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ for $0.125<~x<~0.5,$ and ${\mathrm{La}}_{0.67}({\mathrm{Ca}}_{1-y}{\mathrm{Ba}}_y{)}_{0.33}{\mathrm{MnO}}_3$ for $0<~y<~1$ are shown to directly reflect changes of the structure and of the magnetic state at a local level. For low x values in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ evidence is given about the presence of polaronic lattice distortions. By increasing x, structurally undistorted conductive ferromagnetic (FM) regions are formed indicating a percolative metal to insulator phase transition, whereas for $x=0.5\mathrm{}$ the system is shown to break into FM and antiferromagnetic regions in accordance with the predictions of the electronic phase separation model.