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 La1-xAg xMnO3 and La0.67Ca0.33Mn 1-xRuxO3. Infact, two peaks on ρ(T) curve coexist: broad one at some Tmax below the Curie points (T C) of these compounds and a sharp peak near TC. Authors interpreted such coexistence as an evidence of electronic/magnetic phase separation in the above-noted systems below its TC. It is shown in this comment that such an interpretation is obviously invalid for La 1-xAgxMnO3 system and is very questionable for La0.67Ca0.33Mn1-xRuxO3. 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.
- Electrical resistivity
- Grain-boundary effects
- Polycrystalline-doped manganites