Mössbauer study of colossal magnetoresistive La[sub 1-x]Sr[sub x]Mn[sub 0.9]Fe[sub .1]O[sub 3] (x=0,0.1,0.2,0.3)

Includes bibliographical references (pages [61]-62)The Mössbauer effect is a phenomenon that makes it possible to study local magnetic and electric interactions. General concepts along with computational methods are introduced in the theoretical part of this thesis. Mössbauer studies have been conducted on ^57Fe doped colossal magnetoresistive rare-earth transition metal oxides. Temperature dependent Mössbauer effect, magnetization and resistivity measurements have been made for La[sub 1-x]Sr[sub x]Mn[sub 0.9]Fe[sub .1]O[sub 3] (x=0,0.1,0.2,0.3). Various techniques of synthesis (air, Ar, quenching, slow cooling) were used to create compounds that are virtually free of defects. The 57Fe was shown to have a valence state of 3+ from the Mössbauer effect measurements. As x increases, the crystal structure changes from monoclinic to orthorhombic to rhombohedral, and the transport properties change from antiferromagnetic-semiconductor to ferromagnetic-semiconductor to ferromagnetic-colossal magnetoresistive metal. The Mössbauer effect shows broader distributions of magnetic fields below the magnetic ordering temperature as x is increased. The experimental results are discussed in terms of local structure and time-dependent magnetic exchange interactions.M.S. (Master of Science