Effect of bandwidth and size disorder on the electrical and magnetotransport properties of doped LaMnO₃ perovskite

Abstract

Structural, electrical, magnetic and magnetotransport measurements have been carried out on La_1-2x Pr_xCa_xMnO₃: x =0.20 and 0.30 manganite compounds. These samples form in a distorted orthorhombic structure and behave as nearly low bandwidth systems. Both these samples exhibit insulator-metal transition below 120 K with a large colossal

magnetoresistance (CMR) effect at relatively weaker fields (MR=75% at 1 Tesla for x = 0.30 sample).We have also studied the structural, transport and magnetotransport properties of a larger size cation, Sr²⁺, substituted La_0.5Pr_0.2Ca_0.3-xSr_xMnO₃(0.0≤x≤0.20) compounds. It is observed that increasing Sr²⁺ substitution results in an enhancement in transition temperature with a subsequent fall in MR%. The insulator-metal transition temperature for these samples increases from 138 K for x=0.0 to 252 K for x=0.20. The CMR effect fall from 46% for x=0.0 to less than 10% for x=0.20 at a field of 1 Tesla. Also, for samples with higher Sr content the MR% at low temperature is comparable to the MR% in the vicinity of peak resistance. The resistance data in the semiconducting region of all the samples obeys the Mott’s Variable Range Hopping type(ln<i>R</i> <span style="mso-bidi-font-size:16.0pt;font-family:"Arial Unicode MS","sans-serif"; mso-ansi-language:NL" lang="NL"><img src='http://www.niscair.res.in/jinfo/infinity.gif' border=0>

<i>T</i>^0.25)<i> </i>of conduction mechanism.

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