Title

Local structural, vibrational, and magnetic studies in transition metal alloys and ruthenate oxides

Date of Completion

January 2001

Keywords

Physics, Condensed Matter

Degree

Ph.D.

Abstract

Local structural, vibrational, and shear properties of transition metal alloys have been studied by means of temperature dependent x-ray absorption fine structure (XAFS). Nuclear magnetic resonance (NMR) along with supplementary magnetization and x-ray diffraction has been used to investigate the effect of doping on the local and long range magnetic properties in ruthenate oxides. The work on transition metal alloys concentrates on the β-phase aluminides RuAl, PdAl and ternary dopants in NiAl and various 3d and 4d transition metal dopants in fcc Ni. The site selectivity and local shear properties of Ru and Pd dopants in β-phase NiAl has been studied. It is found that both Ru and Pd dopants go to the Ni sublattice. We find a large local shear resistance for Ru dopants in NiAl relative to Pd dopants in NiAl. Temperature dependent XAFS has been used to study the local lattice dynamical and shear properties of 3d and 4d dopants in fcc Ni. We find that Rh dopants in fcc Ni have the highest local shear resistance as compared to the other 3 d and 4d dopants studied. ^ In order to understand the microscopic origin of the magnetic properties, a zero-field spin-echo NMR study of the 99,101Ru nuclei in polycrystalline samples of the ruthenate system Sr1-xCaxRuO 3 has been carried out. A significant reduction of intensity is observed with the addition of Ca, suggesting progressive loss of Ru moments participating in magnetic ordering. The loss is attributed to the dilution of ferromagnetic exchange coupling between the moments and will be discussed in terms of its crystal structure. ^