Electronic Theses and Dissertations

Identifier

6782

Date

2021

Document Type

Thesis

Degree Name

Master of Science

Major

Physics

Concentration

Materials Science

Committee Chair

Sanjay R Mishra

Committee Member

Muhammad S Jahan

Committee Member

Shawn David Pollard

Abstract

Manganites have shown potential application as magnetic refrigerants due to the exhibition of near room temperature magnetocaloric effect. High relative cooling power (RCP) values and the easy tunability of magnetic phase transition temperature (Tc), magnetic entropy change (?Sm), and RCP opens up a lot of possibilities for exploring better magnetocaloric materials. Reported literature shows doped manganites and composites with significant improvement in magnetocaloric properties. In this work, we have synthesized (1-x) La0.7Ca0.3MnO3-xMO (x = 2.5%, 5%; M = Ni, Cu, Co), magnetite-metal oxide nanocomposites using a simple autocombustion method. The structural and magnetic measurements have been made to explore the purity and the magnetocaloric properties of the sample. The x-ray diffraction data (XRD) of all the samples show the presence of a pure LCMO phase. The presence of metal oxides is further confirmed by energy-dispersive spectroscopy (EDS). The field Cooled magnetization curve shows that the material undergoes second-order PM-FM transition as we decrease the temperature. The obtained phase transition temperature (Tc) drops with the increasing content of metal oxides. The highest drop of Tc is observed from 258 K in pure LCMO to 166.6 K in LCMO-5%CoO. Isothermal magnetization curves for the composites also show PM-FM phase transition with the change in nature of the curve. The maximum magnetic entropy change (?Smax) is observed around Tc for all the samples, and it increases with the increase in the applied field. The largest drop in?Smax is observed from 8.77 JKg-1K-1 in pure LCMO to 3.24 JKg-1K-1 in LCMO-5%NiO. The most important parameter in quantifying the magnetocaloric behavior of the sample, RCP, is calculated, and it is found to increase linearly with the externally applied field. The RCP values increase with the increase in metal oxide content despite the decrease in?Smax. The highest value for RCP obtained is 266.89 JKg-1 in LCMO-5%CuO, which is a 23.4% gain from 213.13 JKg-1 for pure LCMO. The increase in RCP values with the increase in metal oxide content signifies that we were able to tune and improve the magnetocaloric behavior of LCMO by composite formation.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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