Kimball, Clyde W.
M.S. (Master of Science)
Department of Physics
Rare earth metal compounds--Magnetic properties; Mössbauer spectroscopy; X-ray spectroscopy
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].
Qattan, Issam A., "Mossbauer, resistivity, magnetization, and powder x-ray diffraction studies of colossal magnetoresistive La[sub 0.88] Sr[sub 0.12] Mn[sub 1-y] Fe[sub y] O[sub3] (y = 0, 0.02, and 0.04)" (1999). Graduate Research Theses & Dissertations. 4052.
viii, 112 pages
Northern Illinois University
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