Inducement of Itinerant Electron Transport in Charge-Ordered Pr0.6Ca0.4MnO3 by Ba Doping

Abstract

The effects of Ba 2+ doping on the electrical and magnetic properties of charge-ordered Pr0.6Ca0.4MnO3 were investigated through electrical resistivity and AC susceptibility measurements. X-ray diffraction data analysis showed an increase in unit cell volume with increasing Ba 2+ content indicating the possibility of substituting Ba 2+ for the Ca-site. Electrical resistivity measurements showed insulating behavior and a resistivity anomaly at around 220 K. This anomaly is attributed to the existence of charge ordering transition temperature, $T^{\mathrm {R}}_{\text {CO}}$ for the x = 0 sample. The Ba-substituted samples exhibited metallic to insulator transition (MI) behavior, with transition temperature, T MI, increasing from ∼98 K (x = 0.1) to ∼122 K (x = 0.3). AC susceptibility measurements showed ferromagnetic to paramagnetic (FM-PM) transition for Ba-substituted samples with FM-PM transition temperature, T c, increasing from ∼121 K (x = 0.1) to ∼170 K (x = 0.3), while for x = 0, an antiferromagnetic to paramagnetic transition behavior with transition temperature, T N, ∼170 K was observed. In addition, inverse susceptibility versus T plot showed a deviation from the Curie–Weiss behavior above T c, indicating the existence of the Griffiths phase with deviation temperature, T G, increasing from 160 K (x = 0.1) to 206 K (x = 0.3). Magnetoresistance, MR, behavior indicates intrinsic MR mechanism for x = 0.1 which changed to extrinsic MR for x > 0.2 as a result of Ba substitution. The weakening of charge ordering and inducement of ferromagnetic metallic (FMM) state as well as increase in both T c and T MI are suggested to be related to the increase of tolerance factor, τ, and increase of e g −electron bandwidth as average ionic radius at A-site, <r A> increased with Ba substitution. The substitution may have reduced MnO6 octahedral distortion and changed the Mn–O–Mn angle which, in turn, promotes itinerancy of charge carrier and enhanced double exchange mechanism. On the other hand, increase in A-site disorder, which is indicated by the increase in σ 2 is suggested to be responsible for the widening of the difference between T c and T MI.