Strong enhancement of the ferromagnetic phase and local order in Ru substituted manganites studied by EXAFS and dc magnetization measurements

•Ruthenium doping determines a strong enhancement of the ferromagnetic phase component.•The local order increases against the additional disorder due to charge ordering.•The natural tendency to nanometric phase separation of manganites is verified.

We report extended X-ray absorption fine structure (EXAFS) and dc magnetization measurements performed on (La1-xCax) (Mn1-yRuy)O3 samples (x = 0.37 and 0.75 and y = 0.03 or 0.08).In the nanoscale phase inhomogeneity scenario characteristic of these complex oxides, we compare the effects induced by the partial substitution of Mn with mixed valence non-Jahn-Teller Ru5+ and at most very weak Jahn-Teller Ru4+ ions with those induced by the already studied analogous substitutions of Mn with non-Jahn-Teller Cr3+ or Ni2+ or Jahn-Teller Cu2+.We find evidence both from dc magnetization and EXAFS that the ruthenium doping induces a huge effect, clearly enhancing (more efficiently than is the case for the other dopants) the double exchange effect and consequently the metallic/ferromagnetic phase and the local structural order at the expenses of the charge-ordered phase component. In the x = 0.75 long-range charge-ordered system these effects are much more evident, as expected, while for x = 0.37 the magnetic ion partial substitution does not significantly modify the metal-insulator and ferromagnetic transitions, already present in the parent compound.

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