Controlling magnetic structure in extended solids using targeted chemical compositions

dc.contributor.advisor Gordon J Miller Brgoch, Jakoah
dc.contributor.department Chemistry 2018-08-11T14:05:36.000 2020-06-30T02:41:37Z 2020-06-30T02:41:37Z Sun Jan 01 00:00:00 UTC 2012 2013-06-05 2012-01-01
dc.description.abstract <p>The ability to combine experiment and theory provides the framework for targeting compositions that may exhibit a fascinating magnetic response such as ferromagnetism, antiferromagnetism, or ferrimagnetism. Using solid-state synthesis techniques, structural characterization, and theoretical analysis, two intermetallic borides series were analyzed for their magnetic properties. In M<sub>2</sub>M′(T<sub>1-x</sub>T′<sub>x</sub>)<sub>5</sub>B<sub>2</sub> (M = Sc, Ti, Zr; M′ = 3d element; T/T′ = Ru, Rh, Ir), the M′ atom forms chains that when occupied by magnetic atoms, i.e., Mn, Fe, Co, Ni, have interatomic bond distances short enough for one-dimensional, long-range magnetic ordering. The prototypical series, Sc<sub>2</sub>Fe(Ru<sub>1-x</sub>Rh<sub>x</sub>)<sub>5</sub>B<sub>2</sub> (0 ≤ x ≤ 1), was previously identified to change from antiferromagnetic in the Ru-rich structures to ferromagnetic in the Rh-containing compounds. The change in magnetic ordering as a function of composition stems from the occupation of antibonding states at the Fermi level. As a result, theoretical techniques were utilized to identify additional compositions that may form this structure type and show this same unique trend in magnetism. The discovery of a Zr series, by directed synthesis, provided further unique magnetic response by being the first intermetallic boride to order ferrimagnetically.</p> <p>Additionally, the structures of Ti<sub>9−y</sub>M<sub>2+y</sub>Ru<sub>18</sub>B<sub>8</sub>, contains M atoms that form dumbbells of Fe atoms in the ab-plane that condense along the c-direction to form ladders. When Ti atoms are substituted by the M atoms (y = ca. 1-2) the resulting structure contains one-dimensional, single-atom chains (as in the M<sub>2</sub>M′T<sub>5</sub>B<sub>2</sub> series) and one-dimensional ladders (as in the Ti<sub>9</sub>M′<sub>2</sub>T<sub>18</sub>B<sub>8</sub> series) in the same compound. The synthesis of Ti<sub>8</sub>Fe<sub>3</sub>Ru<sub>18</sub>B<sub>8</sub> was the first compound to show both of these subunits in the same structure. Since the bond distances between the chain and ladder sites is only ca. 3.00 Å, the magnetic atoms form a linear tetramer that we have termed a "magnetic scaffold". Furthermore, Ti<sub>8</sub>Fe<sub>3</sub>Ru<sub>18</sub>B<sub>8</sub> contains two separate, one-dimensional chain sites allowing independent local magnetic ordering ultimately providing a system to discover new intermetallic ferrimagnets. In fact, experimental investigations indicate Ti<sub>8</sub>Fe<sub>3</sub>Ru<sub>18</sub>B<sub>8</sub> and the isotypic Ti<sub>7</sub>Fe<sub>4</sub>Ru<sub>18</sub>B<sub>8</sub> order ferrimagnetically. Computational results identified complex magnetic exchange in the magnetic scaffold as the origin of the ferrimagnetism in these structures.</p> <p>The composition-property relationship was extended to investigate non-stoichiometry in tetragonal iron sulfide (Fe<sub>1+δ</sub>S). A delicate balance between the Madelung energy and the occupation of antibonding orbitals drives the inclusion of interstitial Fe in this structure. The additional Fe atoms change the Fermi surface, as well as create a spin density wave. These predicted changes in properties have implications for identifying potential superconductivity in the new Fe-based compounds.</p>
dc.format.mimetype application/pdf
dc.identifier archive/
dc.identifier.articleid 3292
dc.identifier.contextkey 3437650
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath etd/12285
dc.language.iso en
dc.source.bitstream archive/|||Fri Jan 14 19:17:14 UTC 2022
dc.subject.disciplines Chemistry
dc.subject.disciplines Inorganic Chemistry
dc.subject.keywords Crystal Chemistry
dc.subject.keywords Electronic Structure Calculations
dc.subject.keywords Intermetallics
dc.subject.keywords Magnetic Chains
dc.title Controlling magnetic structure in extended solids using targeted chemical compositions
dc.type article
dc.type.genre dissertation
dspace.entity.type Publication
relation.isOrgUnitOfPublication 42864f6e-7a3d-4be3-8b5a-0ae3c3830a11 dissertation Doctor of Philosophy
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