Comment on papers “Effect of Ag substitution on the transport property and magnetoresistance of LaMnO3” [J. Magn. Magn. Mater. 248 (2002) 26] and “Possible magnetic phase separation in Ru-doped La0.67Ca0.33O3” [J. Magn. Magn. Mater. 257 (2003) 195]

Abstract In recent papers Ye et al. (J. Magn. Magn. Mater. 248 (2002) 26) and Lakshmi et al. (J. Magn. Magn. Mater. 257 (2003) 195) reported the characteristic features of electrical resistivity ( ρ ) versus temperature ( T ) dependences of polycrystalline-doped manganites La 1− x Ag x MnO 3 and La 0.67 Ca 0.33 Mn 1− x Ru x O 3 . Infact, two peaks on ρ ( T ) curve coexist: broad one at some T max below the Curie points ( T C ) of these compounds and a sharp peak near T C . Authors interpreted such coexistence as an evidence of electronic/magnetic phase separation in the above-noted systems below its T C . It is shown in this comment that such an interpretation is obviously invalid for La 1− x Ag x MnO 3 system and is very questionable for La 0.67 Ca 0.33 Mn 1− x Ru x O 3 . The simplest and natural reason for the appearance of considered features on ρ ( T ) dependences of polycrystalline manganites is the well-known grain-boundary effects.