Publication Date

1999

Document Type

Dissertation/Thesis

First Advisor

Kimball, Clyde W.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Physics

LCSH

Rare earth metal compounds--Magnetic properties; Mössbauer spectroscopy; X-ray spectroscopy

Abstract

Mossbauer, resistivity, magnetization, and powder x-ray diffraction measurements have been made on La[sub 0.88] Sr[sub 0.12 Mn[sub 1-y] ^57Fe[sub y] O[sub 3] (y = 0.02, and 0.04), while measurements on the y = 0.0 sample have been made with all of the above techniques but Mossbauer. ^57Fe is found to be in the (+3) valance state. The effect of increasing ^57Fe doping level on the structural, magnetic, and transport properties of the colossal magnetoresistive rare-earth transition metal oxides is discussed in detail. I have observed a drop in the static orbital ordered coherent Jahn-Teller distortion temperature T[sub [pi]] and an increase in the ferromagnetic ordering temperature T[sub C] with increasing ^57Fe doping level. A strong suppression of the coherent Jahn-Teller distortion due to magnetization is seen suggesting the existence of magneto-lattice-transport coupling. Anisotropic ferromagnetic spin-wave behavior is the main dynamical character of these samples at low temperatures. Such effect gives rise to gap formation and therefore spin canting in these samples. As y increases, the exchange coupling constant increases and the gap energy decreases. This suggests a strong coupling between the exchange coupling constant and the gap energy at low temperatures. Increasing the exchange coupling constant increases the linkage angle of the ^57Fe^+3 - O^-2 - Mn^+3 network and, therefore, increases T[sub C].

Comments

Includes bibliographical references (pages [110]-112).

Extent

viii, 112 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

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