Possible magnetic phase separation in Ru-doped La0.67Ca0.33MnO3

X-ray diffraction,. resistivity, AC susceptibility and magnetization studies on La0.67Ca0.33Mn1-xRuxO3 (0 less than or equal to x less than or equal to 0.085) were carried out. A significant increase in the lattice parameters indicated the presence of mixed valence state of Ru: Ru3+ and Ru4+. The resistivity of the doped compounds exhibited two features: a broad hump and a relatively sharp peak. While a para- to ferromagnetic transition could be observed for the latter peak, no magnetic signal either in AC susceptibility or in magnetization measurements could be observed for the broad hump. The magnetic-moment of Mn per unit cell decreases non-linearly from 3.55 to 3mu(B) for the Ru compositions studied. Based on the results of the present studies and existing literature on Mn-site substituted systems, we argue that a magnetic phase separation ocqurs in the Ru-doped system. While the sharp peak in the resistivity corresponds to Ru4+-enriched regions with ferromagnetic coupling of Ru with the neighboring Mn ions, the broad peak corresponds to Ru3+-rich regions, with anti ferromagnetic coupling of Ru with the neighboring Mn ions. (C) 2002 Published by Elsevier Science B.V.