Polarons and phase separation in lanthanum-based manganese perovskites:: A 139La and 55Mn NMR study

Low-temperature La-139 and Mn-55 NMR line shape measurements in La1-xCaxMnO3 for 0.125 less than or equal to x less than or equal to 0.5, and La-0.67(Ca1-yBay)(0.33)MnO3 for 0 less than or equal to y less than or equal to 1 are shown to directly reflect changes of the structure and of the magnetic state at a local level. For low x values in La1-xCaxMnO3 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 the system is shown to break into FM and antiferromagnetic regions in accordance with the predictions of the electronic phase separation model. [S0163-1829(99)04609-3].