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Synthesis of Magnetic Ternary Chalcogenides and Their Magneto-Structural Properties.

Author(s) : COMPTON R. J.

Type of monograph: Doctoral thesis

Summary

Magnetism plays a vital role in the technologies of today, and materials used for magnetic applications largely consist of solid state phases. Intermetallic chalcogenides are one such material which have exhibited a full range of properties useful for a variety of applications requiring soft magnets, superconductors, magnetocalorics, and even rarer magnetic phenomenon such as 1D Heisenburg magnetic chains. Solid state chemists continue to develop new synthesis methods for chalcogenides as they produce both new phases and modifications of existing phases, usually with the express intent of improving their physical and chemical properties. Low dimensional chalcogenides often have predictable structure-property relationships which when understood aids in these efforts of optimizing existing materials.

In this work, we have synthesized novel, low-dimensional Tl1-xAxFe3Te3 (A = K, Na)-based magnetocalorics for magnetic refrigeration technologies utilizing a variety of synthetic methods. Doping of alkali metals into the thallium site simultaneously reduces the toxicity and cost of the material, and also modifies their crystal structures leading to changes in their magnetic properties including ordering temperature, magnetic anisotropy, magnetic hysteresis, coercivity, and magnetic entropies. Most notably, the magnetic ordering temperature has been boosted from 220 K of the prior known TlFe3Te3 phase up to 233 K in the new Tl0.68Na0.32Fe2.76Te3.32 phase, further towards room temperature which is required for the commercialization of magnetic refrigerants for home appliances. There exist strong magnetostructural correlations for most of the alterations in the magnetic properties, and relationships have been modelled where trends exist to match the magnetism to the changes in the unit cell of the structure.

New synthetic methods were also developed for the ternary TBi4S7 (T = transition metal) phase which exhibits a pseudo-1D structure of Heisenberg antiferromagnetic chains. These synthetic techniques resulted in more consistent high purity of phases than methods reported previously in literature. Attempts at synthesizing new phases were made, and crystallographic and composition analysis methods suggested the synthesis of a new Mn1-xCoxBi4S7 phase, though magnetic impurities prevented characterization of this new material’s magnetic properties.

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Pages: 121 p.

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