Doctoral Dissertations

Keywords and Phrases

Cr

Abstract

"The La₁₋ₓSrₓMn1-yByO₃ perovskite systems where B represents a 3d transition metal such as Cr, Fe, Co, Ni, Cu, and Zn, are of significant interest due to their large magnetoresistance, and electronic transport properties that change significantly, depending on values of x and which transition metal used. Their applications in technology include cathodes for solid oxide fuel cells, resistance random access memory and catalysis. At certain doping concentrations on the B-site, metal-to-semiconductor or metal-to-insulator transitions coupled with colossal magnetoresistance occur, decreasing the resistivity (up to six orders of magnitude) upon the application of an external magnetic field. The Curie and Neel transition temperatures, TC and TN respectively, can be modified depending on the amount of transition metal substitution. In the parent system, La₁₋ₓSrₓMn³⁺1-xMnₓ4+O₃ at x=0.4, the maximum transition temperatures TMaxC is reached in the La-based manganites.

To better understand the structural and magnetic properties of the 3d transition metal substituted perovskite La₀.₇Sr₀.₃Mn³⁺₀.₇₋ₓMn⁴⁺0.3B³⁺ₓ+O₃, we studied the effects of replacing B with Cr and Ni atoms using x-ray and neutron diffraction and magnetic measurements. Of these two 3d transition metals, Cr has the least occupied outer valence shells, (Ar) 3d⁵4s¹ and has the same t2g electronic configuration as Mn⁴⁺, while Ni has the most filled outer valence shells, (Ar) 3d⁸4s². The configurations of these outer valence electrons play a substantial role in the resultant magnetic interactions as witnessed by the unexpected magnetic ordering differences observed in the Cr and Ni-substituted systems. An extensive literature search indicated no previous neutron diffraction studies had been carried out for these two systems"--Abstract, page iv.

Advisor(s)

James, William Joseph
Pringle, Oran Allan

Committee Member(s)

Yelon, William B.
Parris, Paul Ernest, 1954-
Vojta, Thomas

Department(s)

Physics

Degree Name

Ph. D. in Physics

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2013

Pagination

xiv, 137 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2013 Thomas Franklin Creel , Jr., All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Ferromagnetic materials -- Fluctuations
Neutrons -- Diffraction
Calcium titanate
Transition metal compounds
Magnetoresistance
Energy levels (Quantum mechanics)

Thesis Number

T 10313

Electronic OCLC #

853507818

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