Grain boundary effects on the electrical and magnetic properties of Pr_(2/3)Ba_(1/3)MnO_3 and La_(2/3)Ca_(1/3)MnO_3 manganites

摘要

Electrical and magnetic properties of orthorhombic Pr_(2/3)Ba_(1/3)MnO_3 (PBMO) and La_(2/3)Ca_(1/3)MnO_3 (LCMO) manganites with considerable difference in variance factors (σ~2) are reported here. PBMO with higher variance exhibits distinct intrinsic (due to grains) and extrinsic (due to grain boundaries) transitions in the resistivity behaviour. Extrinsic effects, however, are not observed in the lower σ~2 LCMO system. Low field magnetoresistivity (LFMR) data also substantiate these results. Increase in the density of states obtained through Mott's 3-D variable range hopping mechanism in the paramagnetic insulating regime indicates the suppression of magnetic domain scattering with applied magnetic field. Ferromagnetic metallic regime below the extrinsic transition in PBMO seems to emanate from the electron-magnon scattering process. LFMR at 77 K also points towards the higher canting of spins in the vicinity of grain boundary regions in PBMO compared to that in LCMO.