<p>The applications of magnetic materials are related to their magnetic and crystal structure as well as electronic properties. In this thesis, mainly experimental methods have been focussed on novel materials and bulk materials. A selection of materials were studied by several techniques like Mössbauer spectroscopy, X-ray and neutron diffraction and magnetisation measurements.</p><p>New technology allow us to prepare artificial materials with unic magnetic properties. Magnetic multilayers are very interesting not only from phenomenological point of view but also as good applications materials. In this work will be shown some results from Fe/V and Fe/Co multilayer system</p><p>The (Fe_1-xMn_x)₃P system has been studied at both ends of the composition range. At the Fe-rich end, compounds exhibiting ferromagnetic ordering are formed, while at the Mn-rich end, an antiferromagnetic coupling was discovered. The experimental results are supported by theoretical calculations.</p><p>Rare-earth compounds with focus on Fe_0.65Er_0.2B_0.15 were studied by means of traditional Mössbauer spectroscopy, Monochromatic Circular Polarized Mössbauer Spectroscopy, X-ray diffraction and magnetic mesurements. This compound shows interesting behaviour of Fe magnetic moment at low and room temperature.</p><p>The first magnetic studies on rhombohedral Li₃Fe₂(PO₄)₃ at low temperature has also been made and an antiferromagnetic structure was revealed.</p>

<p>The magnetic properties of transition metal compounds have been studied using SQUID-magnetometry, magnetic force microscopy and Lorentz transmission electron microscopy. New magnetic materials have been found and their magnetic properties have been determined. How the magnetic properties of a material can be changed through e.g. chemical substitution of magnetic and nonmagnetic atoms and shape and size effects have also been studied. Three different sets of samples have been investigated: three new Mn-compounds, two substitution series of layered magnetic structures and ferromagnetic micronsized thin film elements.</p><p>The three Mn-compounds, Mn₃IrSi, IrMnSi and Mn₈Pd₁₅Si₇, show different magnetic ordering. Mn₃IrSi orders 'antiferromagnetically' at 210 K. IrMnSi forms a double cycloidal spin spiral below 460 K. Mn₈Pd₁₅Si₇ only shows short-range magnetic ordering.</p><p>Substituting Se with S in TlCo₂Se_2-xS_x changes the magnetic order from a spin spiral to a colinear ferromagnet for a composition of <i>x</i>=1.75. An intermediate region exists where the compound is neither a pure ferromagnet, nor purely a spin spiral, as evidenced by the magnetization versus field measurements for the <i>x</i>=1.3 and 1.5 samples. This is also seen in the temperature dependent susceptibility measurements. For the TlCu_2-xFe_xSe₂ compounds it was found that the ordering temperature and saturation magnetic moment per Fe-atom changed with composition <i>x</i>.</p><p>Ferromagnetic micronsized thin film elements in permalloy, Fe₂₀Ni₈₀, and epitaxial Fe/Co multilayers were studied. For the Fe/Co multilayer thin film elements it was found that it is possible to change the magnetization reversal process, by aligning the easy shape anisotropy axis with either the easy or the hard magnetocrystalline anisotropy axis. In the permalloy elements the effect of inter-elemental distance was found to determine the interval of fields where multidomain states were stable, so that for shorter inter-elemental distances multidomain states were stable for a shorter interval of fields. The domain structure of permalloy elements in rotating magnetic fields was also studied. Higher applied fields led to a broader interval of angles in which saturated states were stable.</p>

The applications of magnetic materials are related to their magnetic and crystal structure as well as electronic properties. In this thesis, mainly experimental methods have been focussed on novel materials and bulk materials. A selection of materials were studied by several techniques like Mössbauer spectroscopy, X-ray and neutron diffraction and magnetisation measurements. New technology allow us to prepare artificial materials with unic magnetic properties. Magnetic multilayers are very interesting not only from phenomenological point of view but also as good applications materials. In this work will be shown some results from Fe/V and Fe/Co multilayer system The (Fe1-xMnx)3P system has been studied at both ends of the composition range. At the Fe-rich end, compounds exhibiting ferromagnetic ordering are formed, while at the Mn-rich end, an antiferromagnetic coupling was discovered. The experimental results are supported by theoretical calculations. Rare-earth compounds with focus on Fe0.65Er0.2B0.15 were studied by means of traditional Mössbauer spectroscopy, Monochromatic Circular Polarized Mössbauer Spectroscopy, X-ray diffraction and magnetic mesurements. This compound shows interesting behaviour of Fe magnetic moment at low and room temperature. The first magnetic studies on rhombohedral Li3Fe2(PO4)3 at low temperature has also been made and an antiferromagnetic structure was revealed.

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Rina Tannenbaum; Committee Co-Chair: Rosario A. Gerhardt; Committee Member: E. Kent Barefield; Committee Member: Karl I. Jacob; Committee Member: Preet Singh; Committee Member: R. Bruce King. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The magnetic properties of transition metal compounds have been studied using SQUID-magnetometry, magnetic force microscopy and Lorentz transmission electron microscopy. New magnetic materials have been found and their magnetic properties have been determined. How the magnetic properties of a material can be changed through e.g. chemical substitution of magnetic and nonmagnetic atoms and shape and size effects have also been studied. Three different sets of samples have been investigated: three new Mn-compounds, two substitution series of layered magnetic structures and ferromagnetic micronsized thin film elements. The three Mn-compounds, Mn3IrSi, IrMnSi and Mn8Pd15Si7, show different magnetic ordering. Mn3IrSi orders 'antiferromagnetically' at 210 K. IrMnSi forms a double cycloidal spin spiral below 460 K. Mn8Pd15Si7 only shows short-range magnetic ordering. Substituting Se with S in TlCo2Se2-xSx changes the magnetic order from a spin spiral to a colinear ferromagnet for a composition of x=1.75. An intermediate region exists where the compound is neither a pure ferromagnet, nor purely a spin spiral, as evidenced by the magnetization versus field measurements for the x=1.3 and 1.5 samples. This is also seen in the temperature dependent susceptibility measurements. For the TlCu2-xFexSe2 compounds it was found that the ordering temperature and saturation magnetic moment per Fe-atom changed with composition x. Ferromagnetic micronsized thin film elements in permalloy, Fe20Ni80, and epitaxial Fe/Co multilayers were studied. For the Fe/Co multilayer thin film elements it was found that it is possible to change the magnetization reversal process, by aligning the easy shape anisotropy axis with either the easy or the hard magnetocrystalline anisotropy axis. In the permalloy elements the effect of inter-elemental distance was found to determine the interval of fields where multidomain states were stable, so that for shorter inter-elemental distances multidomain states were stable for a shorter interval of fields. The domain structure of permalloy elements in rotating magnetic fields was also studied. Higher applied fields led to a broader interval of angles in which saturated states were stable.

The design, synthesis, characterization, and applications of annulated bis(imidazolium) salts are described. New synthetic methodologies have been developed that allow access to a broad structural range of bis(imidazolium) salts. Initial studies focused on thee use of bis(imidazolium) salts as comonomers in the formation of mainchain organometallic polymers. Two distinct polymer scaffolds were synthesized, one featuring metal(II)dihalides in the main-chain, and the other featuring a chelated metal center. Ultimately, polymerizations were conducted under ambient atmosphere, proceeded in excellent overall yield, and provided main-chain organometallic polymers comprising Ni(II), Pd(II), and Pt(II) with molecular weights up to 106 Da. Departing polymer studies, focus was shifted toward the study of the physical and photophysical properties of the bis(imidazolium) salts. In few synthetic manipulations, a series of highly photoluminescent bis(imidazolium) salts were prepared whose substituents enable emission in solution, in the solid-state, and, uniquely, as free-flowing liquids. Importantly, these materials display excellent physical properties, such as low glass-transition temperatures (< 0 °C) and high thermal stabilities (> 300 °C). In addition, the bis(imidazolium) platform enabled access to two new fluorescent ionic liquid crystals, demonstrating an ability to also control mesomorphic properties of these materials. Further investigations were conducted regarding the photophysical properties of bis(imidazolium) salts. Focus was placed upon absorption and emission wavelength tunability, solvatochromism, red-edge excitation, and chemical stability. Through functional group modulation, the [lambda]em were varied from 329 -- 561 nm with [Phi]fs up to 0.91. Both the absorption and emission characteristics were found to display strong solventdependencies which were found to be strongly influenced by the nature of the bis(imidazolium) core. The red-edge effect was investigated for a series of bis(imidazolium) salts and was found to be similar between Br and BF4 salts, but distinctly different when MeSO4 anions were incorporated. The stability of an amphiphilic BBI was quantified in aqueous solutions of varying pH and > 85% of the emission intensity was retained after 2 h at pH levels of 3 -- 9.

Thesis (Ph. D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5229. Supervisor: M.J. McGlinchey.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Orientadores: Sergio Gama, Ekkes Bruck / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T04:26:45Z (GMT). No. of bitstreams: 1 Caron_Luana_D.pdf: 3120809 bytes, checksum: 0f270249e6bc452525873f2d4479ba9d (MD5) Previous issue date: 2008 / Resumo: Nesta tese de doutoramento são apresentados os resultados do estudo das propriedades magnéticas, magnetocalóricas e estruturais de algumas séries de compostos que são de interesse para aplicação em refrigeração magnética baseada no efeito magnetocalórico. Os métodos de preparação da série MnFe P1-xAsx são estudados de forma a otimizar o tempo de preparação e as propriedades magnétocalóricas. Uma nova série de compostos baseada na anterior, a MnFeGe1-xSix foi descoberta, apresentando transições de fase magnética de segunda ordem e uma variação linear dos parâmetros de rede em função da concentração de Si no intervalo 0 £ x £ 0,7. Também foi descoberto, associado à uma transição magnética de segunda ordem, o efeito magnetocalórico no composto MnFeSn cujo TC situa-se em torno da temperatura ambiente. Foi feito o estudo do efeito magnetocalórico dos compostos baseados no Mn2Sb com o Mn parcialmente substituído por Cr, V, Co e Cu e o Sb substituído por Ge. Nestes compostos uma transição do tipo Exchange Inversion é induzida pelas substituições, transformando o estado ferrimagnético em antiferromagnético em baixa temperatura, dando origem ao chamado efeito magnetocalórico inverso. Ainda foi desenvolvido um modelo fenomenológico para descrever tal transição e o efeito magnetocalórico associado. Por fim é reportado o efeito magnetocalórico colossal nos compostos M n1-xCux As, devido ao qual os métodos de medida magnéticos do efeito magnetocalórico são revistos. A partir dos resultados em diferentes procedimentos de medida, é proposta uma forma de medir o efeito em materiais altamente histeréticos que não leva a resultados espúrios / Abstract: On this PhD thesis some results on the magnetic, magnetocaloric and structural properties of some series of compounds suitable for applications on magnetocaloric effect-based refrigeration are presented. The FeMnP1-xAsx series preparation methods are studied in order to optimize their magnetocaloric properties as well as to shorten its preparation time. A new series of compounds based on the previous one was studied, the MnFeGe1-xSix. These compounds present a second-order magnetic phase transition and a linear change in lattice parameters with Si content on the 0 £ x £ 0.7 range. Also associated with a second-order phase transition, the magnetocaloric effect on FeMnSn was discovered around room-temperature. A careful study of Mn2Sb-based compounds with Mn partially substituted by Cr, V, Co and Cu and Sb by Ge was performed. On these compounds an Exchange Inversion transition is induced by substitutions taking the material from the ferrimagnetic to the antiferromagnetic state with decreasing temperature, giving rise to the so-called inverse magnetocaloric effect. A phenomenological theoretical model was also developed to describe such transitions and their associated magnetocaloric effect. Finally we report on the colossal magnetocaloric effect on Cu-substituted MnAs compounds. Due to this compound¿s unusual behavior, the magnetic measurements of the magnetocaloric effect are reviewed. Based on the results of different measurement procedures a new method of measurement for highly hysteretic compounds is proposed which leads to non spurious results / Doutorado / Materiais Magneticos e Propriedades Magneticas / Doutor em Ciências