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Approach to the metal-insulator transition in La(1-x)CaxMnO3 (0<x<.2): magnetic inhomogeneity and spin wave anomaly

G. Biotteau·M. Hennion·F. Moussa·L. Pinsard·A. Revcolevschi·Y. M. Mukovskii·D. Shulyatev
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Abstract

We describe the evolution of the static and dynamic spin correlations of La$_{1-x}$Ca$_x$MnO$_3$, 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$<$0.1. The anisotropic q-dependence of the intensity of the low-energy spin wave suggests a bidimensionnal character for the static inhomogeneities. At x=0.125, which corresponds to the occurence of a ferromagnetic and insulating state, the two spin wave branches reduce to a single one, but anisotropic. At this concentration, an anomaly appears at {\bf q$_0$}=(1.25,1.25,0), that could be related to an underlying periodicity, as arising from (1.5,1.5,0) superstructures. At x=0.2, the spin-wave branch is isotropic. In addition to the anomaly observed at q$_0$, extra magnetic excitations are observed at larger q, forming an optical branch. The two dispersion curves suggest an anti-crossing behavior at some {\bf q$_0$'} value, which could be explained by a folding due to an underlying perodicity involving four cubic lattice spacings.

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G. Biotteau, M. Hennion, F. Moussa, L. Pinsard, A. Revcolevschi, Y. M. Mukovskii, D. Shulyatev. 2001-01-26. Approach to the metal-insulator transition in La(1-x)CaxMnO3 (0<x<.2): magnetic inhomogeneity and spin wave anomaly. https://doi.org/10.1103/physrevb.64.104421

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