Mn 4+ holes localization around divalent cations in low‐hole doped manganites

Magnetotransport properties of low Ca doping La 1‐x Ca x MnO 3 perovskite related manganites have been described on the basis of the existence of isolated metallic (M)‐double exchange (DE) ferromagnetic (FM) nanoclusters embedded in a long range insulating (I) matrix. Taking into account the DE mechanism, long range FM order and M conduction are expected across the La 1‐x Ca x MnO 3 series. However, the real behaviour differs from this ideal description as an I state is observed for x£0.2. This can be understood by assuming that the electronic itinerancy is not spread to the whole sample but restricted to FM‐M clusters embedded in the matrix. In spite of much effort devoted to their study, the behavior at atomic level is far from being satisfactorily explained. Here we report direct experimental evidence in La 0.9 Ca 0.1 MnO 3 , by means of STEM‐EELS characterization in a JEOL ARM 200 cFEG aberration corrected microscope, that holes and divalent cations tend to be closely correlated in the sample. Figure 1 shows a characteristic HAADF image and corresponding EELS compositional maps showing a heterogeneous distribution of La and Ca. The study of the Mn oxidation state suggests a shift towards Mn 3+ or Mn 4+ when the environment is La and Ca richer, respectively (figure 2). [1] This Ca‐hole attraction results in the formation of small clusters confined to one or two unit cells and would provide an answer to the long‐standing problem of the origin of the electric and magnetic behavior in the low calcium region of the La 1‐x Ca x MnO 3 system.