Comment on "magnetic field mediated low-temperature resistivity upturn in electron-doped La_1-xHf_xMnO₃ manganite oxides" [J. Appl. Phys. 112, 123710 (2012)]

In a recent paper, Guo et al. [J. Appl. Phys. 112, 123710 (2012)] reported on characteristic features of the temperature (T) and magnetic field (H) dependences of electrical resistivity (ρ) in polycrystalline La _1-xHf_xMnO₃ (x = 0.2 and 0.3) manganites. In particular, shallow minima were observed at some T_min below 100 K on ρ(T) curves. Application of an external H ≤ 5 T leads first to a decrease in the T_min value, while this value increases notably at H > 0.75 T. The authors attributed this complex behavior to competitive electron-electron interaction and Kondo-like spin dependent scattering of carriers. It is shown in the comment that such interpretation is very questionable due to the fundamental inapplicability of this approach for analysis of low-T conductivity in polycrystalline manganites. It seems that the most likely reason for the appearance of the low temperature minima on ρ(T) curves and their evolution upon field application is the well known grain boundary effects in magnetically and structurally inhomogeneous samples.