Approach to the metal-insulator transition in La1-xCaxMnO3 (0≤x≤0.2):: Magnetic inhomogeneity and spin-wave anomaly -: art. no. 104421

We describe the evolution of the static and dynamic spin correlations of La1-xCaxMnO3 for x=0.1, 0.125, and 0.2, where the system evolves from the canted magnetic state towards the insulating ferromagnetic state, approaching the metallic transition (x = 0.22). In the x = 0.1 sample, the observation of two spin-wave branches typical of two distinct types of magnetic coupling and of a modulation in the elastic diffuse-scattering characteristic of ferromagnetic inhomogeneities confirms the static and dynamic inhomogeneous features previously observed at x<0.1. The anisotropic q dependence of the intensity of the low-energy spin wave suggests a bidimensional character for the static inhomogeneities. At x=0.125, which corresponds to the occurrence of a ferromagnetic and insulating state, one spin wave branch, anisotropic, is detected. At this concentration, an anomaly appears at q(0) = (1.25, 1.25, 0). At x = 0.2, the spin-wave branch appears as isotropic. In addition to the anomaly observed at q(0), extra magnetic excitations are observed at larger q, forming an optical branch.