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Mixed exchange interaction: a Structural, electrical, magneto Transport, magnetic and thermal studies Of doped manganites

Manjunatha, S O (2015) Mixed exchange interaction: a Structural, electrical, magneto Transport, magnetic and thermal studies Of doped manganites. Phd. Thesis thesis, Manipal Institute of Technology, MU Manipal.

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Abstract

Manganites which are mixed valent manganese oxides materials, with general formula R1-xAxMnO3 (R - Rare earth ions and A - Alkaline earth ions), have attracted attention of condensed matter physics community due to their fascinating magneto-transport, magnetic and thermal properties. Perovskite manganites are subject of interest due to the rich physics involved. They display rich phase diagram and complex electronic and magnetic properties. They are prototypical of highly correlated electron system where many degrees of freedom like localized spins, itinerant charges, lattice vibrations and electronic orbitals are at play simultaneously and where classical simplifications, that neglect some interactions to study others in detail, simply do not work. They also exhibit several other characteristics like charge ordering (CO), orbital ordering (OO), Jahn-Teller (J-T) distortion effect, double exchange (DE) interactions and phase coexistence. From the past few decades manganites have taken the major research endeavors essentially due to the discovery of colossal magneto resistance (CMR) property observed in La0.67Ca0.33MnO3 system by Jin et al. [1]. These materials have technological applications like magnetic sensors, magnetic read head devices for magnetic data storage and spintronics [2-5]. The term CMR has been adopted to quantify the relative change in resistivity due to the application of external magnetic filed H. Attempts have been made during last few decades to enhance the magnitude of MR driven in order to cater the needs of industry. On the other hand, the discovery of large magnetocaloric effect (MCE) near room temperature in rare earth metal Gadolinium has led to the development of a new magnetic refrigeration technology over conventional gas compression (CGC) technique [6,7]. The former is environmental friendly compared to the latter. The magneto-caloric effect is an adiabatic temperature change or an isothermal entropy change upon the application of a magnetic field. Gadolinium exhibits a large entropy change of ΔSm=10.2 J/kg. K for a change in magnetic field ΔH=5T at TC=276K. [8]. However, usage of Gadolinium is commercially limited due to its high cost. Therefore, research has been focused on the search for commercially feasible potential materials displaying good MCE. A large magnetic entropy change observed in several perovskite manganites with the general formula R1-xAxMnO3 (Rtrivalent rare earth, A-divalent alkaline earth) [9-11] has recently renewed the interest in exploring these materials.

Item Type: Thesis (Phd. Thesis)
Subjects: Engineering > MIT Manipal > Physics
Depositing User: MIT Library
Date Deposited: 16 Jun 2017 10:18
Last Modified: 16 Jun 2017 10:18
URI: http://eprints.manipal.edu/id/eprint/149057

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