Deoxygenation Enhanced Double-Resistivity-Peak Properties in Polycrystalline La_0.7Ca_0.3Mn_0.92Cr_0.08O_3-δ

Influences of deoxygenation on the resistivity and the magnetic properties of
La_0.7Ca_0.3Mn_0.92Cr_0.08O_3-δ(M = Al, Cr) are compared to understand the peculiar doping effect of chromium in the ferromagnetic manganites. It is found that the double resistivity bumps exhibited by the Cr-doped compounds can be tuned by the oxygen content. We have related the double-bump feature with the well-known inefficiency of Cr in lowering T_C, and interpreted both the features consistently in terms of large-scale phase separation. It is suggested that the
large-scale phase separation is a general characteristic of Cr-doped manganites, and many unusual phenomena exhibited by Cr doping are directly related to the large-scale phase separation.