Date of Award

12-1984

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Supervisor

Professor J.E. Greedan

Abstract

The structural and magnetic properties of the tri-rutile phases MTa₂O₆ (M = V, Fe, Co, Ni) were investigated. The nuclear and magnetic structures were refined from neutron powder diffraction data. The magnetic M²⁺ ions are located in planes perpendicular to the c axis. The distance between neighboring planes is approximately 4.5 Å. As a result, these compounds are quasi two dimensional magnetic systems, because the magnetic exchange interaction between ions in (001) planes is much larger than the interaction between ions in neighboring planes.

Evidence for important two dimensional correlations has been obtained from magnetic susceptibility and heat capacity measurements. The magnetic susceptibility of these materials is characterized by a broad maximum at a temperature substantially above the ordering temperature. The experimentally observed magnetic susceptibility was compared to the predictions for 2-d quadratic layer models. The exchange interaction was antiferromagnetic in all cases. NiTa₂O₆ and VTa₂O₆ are Heisenberg systems with S = 1 and S = 3/2, respectively. The magnetic susceptibility of CoTa₂O₆ was consistent with an S = 1/2 Heisenberg model, while FeTa₂O₆ showed Ising-like behavior with S = 11.2.

The magnetic structures of FeTa₂O₆ and VTa₂O₆ were determined. Mössbauer effect measurements were used to distinguish between two possible structural models for FeTa₂O₆. The magnetic moments of the Fe²⁺ ions points along <110> directions. The magnetic structure of VTa₂O₆ is similar, but the V²⁺ moments are oriented along <001>.


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