Electrical, magnetic and thermal Properties of Bi-DOPED RE0.6-xSr0.4MnO3 and RE0.7-xSr0.3MnO3 (RE=Pr, La) manganites

Daivajna, Mamatha D (2014) Electrical, magnetic and thermal Properties of Bi-DOPED RE0.6-xSr0.4MnO3 and RE0.7-xSr0.3MnO3 (RE=Pr, La) manganites. Phd. Thesis thesis, Manipal Institute of Technology, Manipal.

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The present work is undertaken to study the effect of bismuth doping on structural, electrical, magneto-transport, magnetic and thermal properties of RE0.7-xSr0.3MnO3/RE0.6- xSr0.4MnO3 (RE= Pr, La) compounds. Samples of the series bismuth doped RE0.7- xSr0.3MnO3/RE0.6-xSr0.4MnO3 (RE= Pr, La) are prepared by using solid-state reaction method. Pr0.7-xBixSr0.3MnO3 and Pr0.6-x BixSr0.4MnO3 (0≤x≤0.25) are orthorhombic with Pbnm and Pnma space group respectively. Phase transition temperature due to resistivity (TMI), magnetization (TC), thermo-power, thermal conductivity and specific heat increases in Pr0.7-xBixSr0.3MnO3 and decreases in Pr0.6-xBixSr0.4MnO3 (0≤x≤0.25) with Bi. Similarly La0.7-xBixSr0.3MnO3 and La0.6-x BixSr0.4MnO3 (0≤x≤0.3) are rhombohedral with R-3C space group. In these compounds, metalinsulator transition (TMI) and ferromagnetic-paramagnetic (TC) transition temperature due to resisitivty and magnetization decreases with bismuth content. In all compounds metallic region transport mechanism is mainly governed by the electron-electron scattering. The high temperature resistivity data above TMI as well as to estimate activation energy (E) is fitted using small polaron hopping (SPH). The values of E increases in all except at series Pr0.7- xBixSr0.3MnO3 where it decreases with bismuth. Magneoto-resistance (MR%) increases in all compounds except at Pr0.7-xBixSr0.3MnO3 where it decreases with bismuth. It is seen in M-T curves, the difference between FC and ZFC modes becomes more pronounced with increasing Bi substitution in all compounds most likely due to the increase of the magnetic frustration arising from the bending Mn-O-Mn bond. Thermoelectric power data for all the series indicates that the small polaron hopping model is operative in the high temperature paramagnetic phase. Similarly low temperature data suggests that the electron-magnon scattering is essentially responsible for the thermoelectric transport in the FM region in all the compounds. It is found that samples of La0.6-xBixSr0.4MnO3(x=0.25 and 0.3), TEP increases and attains a maximum value at a particular temperature due to enhancement in spin polarization caused by the magnetic transition, thereafter, with further decrease in temperature TEP is observed to decrease. The magneto caloric effect (MCE) is studied in compound Pr0.6-xBixSr0.4MnO3 (x=0 and 0.05).

Item Type: Thesis (Phd. Thesis)
Subjects: Engineering > MIT Manipal > Physics
Depositing User: MIT Library
Date Deposited: 16 Jun 2016 10:48
Last Modified: 16 Jun 2016 10:48
URI: http://eprints.manipal.edu/id/eprint/146365

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