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‣ Ressonância magnética nuclear em materiais magnéticos diluídos aleatoriamente; Nuclear magnetic resonance studies of randomly diluted magnetic systems

Magon, Claudio Jose
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/12/1985 Português
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A dependência com a temperatura dos tempos de relaxação nuclear e da forma da linha de ressonância dos núcleos F0, nos antiferromagnetos diluidos Fex Zn1-x F2 e Mnx Zn1-x F2, foram estudados na faixa TN≤T≤300K. Os tempos de relaxação spin, rede (1/T1) dos núcleos F0, os quais não estão acoplados aos spins Fe (ou Mn) através da interação hiperfina transferida, foram medidos e calculados teoricamente em função da concentração x. Os resultados teóricos apresentam uma boa concordância com os dados experimentais para concentrações na faixa 0.1≤x≤0.8. A dependência com a temperatura de 1/T1, para TN

‣ Estudo da dinâmica molecular em copolímeros em bloco compostos de poli(metacrilato de metila), poli(ácido acrílico) e poli(acrilato de chumbo) por técnicas de ressonância magnética nuclear e análise térmica; Study of Molecular Dynamics in Copolymers of Poly (methyl methacrylate), poly (acrylic acid) and Poly (acrylate lead) by nuclear magnetic resonance and thermal analyses

Silva, André Luis Bonfim Bathista e
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/07/2009 Português
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Esta tese envolveu o estudo da dinâmica molecular em copolímeros em bloco compostos de poli(metacrilato de metila) (PMMA), poli(ácido acrílico) (PAA) e Poli(acrilato de chumbo) (PAPb) por técnicas de Ressonância Magnética Nuclear e de análise térmica (DSC e DMTA). Estes copolímeros em bloco foram sintetizados visando a obtenção de compostos para serem utilizados, tanto como lentes oftálmicas com maiores índices de refração, como materiais dedicados à proteção radiológica, sendo estas duas propriedades de emprego individual ou integrado. Para o estudo destes materiais, as amostras foram confeccionadas com várias composições, incluindo aquelas nas formas puras contendo apenas um bloco, resultantes da combinação de dois blocos, e as triblocos, com diferentes quantidades relativas de PAPb, variando de 1 a 40%. Para o caso do PMMA, a dinâmica molecular é bem conhecida, sendo caracterizada por uma relaxação β, que envolve mais especificamente movimentos de seus ramos laterais e que ocorre dentro de um amplo intervalo de temperatura centrado em torno da ambiente, e pela transição vítrea, que envolve, predominantemente, movimentos da cadeia principal que ocorrem para temperaturas em torno de 100oC. Devido à extensão destes dois eventos em grandes intervalos de temperatura...

‣ Estudo de condutores iônicos vítreos e poliméricos por ressonância magnética nuclear; Nuclear magnetic resonance study of vitreous and polymeric ionic conductors

Frare Junior, Pedro Luiz
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/09/1996 Português
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Neste trabalho apresenta-se um estudo por Ressonância Magnética Nuclear (RMN) dos condutores iônicos vítreos (fluoroindatos) e poliméricos, com base nos Poli-Óxidos de Propileno (PPO). Nosso principal objetivo é investigar as propriedades de RMN dos íons responsáveis pela condução iônica nestes condutores amorfos. Entre as propriedades estudadas estão os mecanismos de relaxação nuclear em função da temperatura e freqüência, a forma de linha e o segundo momento associado as linhas de ressonância. No caso dos complexos poliméricos, nossos resultados indicam que a condutividade é governada pelos movimentos segmentários de cadeia polimérica. A análise do segundo momento das linhas, permitiu determinar a intensidade das interações dominantes que estão envolvidas nestes complexos. Dos resultados de relaxação em polímeros, obtivemos os parâmetros importantes do movimento iônico, tais como: a energia de ativação (Ea), a freqüência de saltos (▨ e a dependência em freqüência da taxa de relaxação. Nossos resultados refletem a natureza desordenada destes materiais e a complexidade do processo de condução iônica nestes sistemas. Nos estudos realizados em vidros fluorados, pudemos discriminar os mecanismos re relaxação spin-rede presentes. Estes resultados mostram que...

‣ Relaxação da magnetização nuclear de água confinada em alumina; Relaxation of the nuclear magnetization water contained in alumina.

Agra, João Tertuliano Nepomuceno
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/02/2002 Português
Relevância na Pesquisa
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Neste trabalho é investigada a relaxação longitudinal da magnetização nuclear de água impregnada em pastilhas de pó de alumina (Al IND. 2 O IND. 3) com grau de pureza de 99,8%, objetivando a determinação do diâmentro de poro de uma espuma cerâmica do mesmo material a partir de medidas do tempo de relaxação longitudinal T IND. 1. O trabalho fundamenta-se no fato dos tempos de relaxação da magnetização nuclear T IND. 1 e T IND. 2, spin-rede e spin-spin respectivamente, de um fluido confinado em um meio poroso serem menores que tempos T IND. 1B e T IND. 2B para o mesmo fluido não confinado. Mediram-se os tempos T IND. 1 para graus de impregnação de água nas amostras entre 10 e 100% usando um espectrômetro montado a partir de módulos comerciais e de um gerador de pulsos desenvolvido no IFSC-USP. A partir dos tempos T IND. 1 e dos diâmetros de poro das pastilhas de pó, determinou-se o valor da relaxatividade longitudinal ou intensidade de relaxação superficial (mu IND. 1), um parâmetro que caracteriza a interface água-alumina nestas amostras. Usando o valor de (mu IND. 1) obtido para o pó e o tempo de relaxação T IND. 1 medido nas amostras de espuma cerâmica foi determinado o diâmetro de poro desta. Última...

‣ Difusão de spins nucleares em meios porosos - uma abordagem computacional da RMN; Nuclear spin diffusion in porous media - a computational approach of NMR

Oliveira, Éverton Lucas de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/02/2015 Português
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A Ressonância Magnética Nuclear (RMN) é uma importante técnica empregada nas principais áreas de conhecimento, tais como, Física, Química e Medicina. Importantes trabalhos da RMN aplicada ao estudo da dinâmica de moléculas em fluidos presentes em meios porosos permitiram que esta técnica ganhasse também notoriedade na indústria do petróleo. O presente projeto é fundamentado em alguns destes trabalhos seminais, reproduzindo, através de modelos físico-computacionais, os principais efeitos físicos da difusão e a consequente relaxação dos spins dos núcleos atômicos presentes nas moléculas dos fluidos imersos nos meios porosos. Os métodos teóricos utilizados para a interpretação dos parâmetros de relaxação transversal (T2) e longitudinal (T1), levam em consideração as propriedades macroscópicas da dinâmica de um ensemble de spins nucleares. Para a compreensão da difusão e relaxação nuclear em meios porosos, é de fundamental importância o emprego de métodos físico-computacionais que levam em consideração tanto a microestrutura quanto a difusão translacional dos spins nucleares através desses meios. Dentro dos modelos propostos nesta dissertação, foram utilizados conceitos básicos de mecânica estatística e de relaxação nuclear...

‣ Processamento digital de sinais aplicado a análise de distribuição de tempos de relaxação em sinais de ressonância magnética nuclear; Digital signal processing applied to relaxation times distribution analysis in nuclear magnetic resonance signals

Queiroz, Guylherme Emmanuel Tagliaferro de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/06/2015 Português
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Sabe-se que a relaxação de líquidos em meios porosos envolve três mecanismos principais: relaxação bulk, relaxação de superfície e difusão. Muitas vezes, os processos de relaxação de líquidos confinados em meios porosos são dominados pelo processo de relaxação de superfície e difusão do fluído. No chamado regime de difusão rápida, a relaxação de um único poro é comandada por uma função mono exponencial que depende, principalmente, da relação superfície-volume do poro, de modo que em um material poroso, isto é, contendo uma distribuição ampla de tamanho de poros, o sinal de decaimento de magnetização obtido por meio da ressonância magnética nuclear é formado pela soma de exponenciais com diferentes tempos de relaxação. O problema-chave abordado neste trabalho consiste, portanto, em obter por meio desse sinal de magnetização a distribuição dos tempos de relaxação que controlam o decaimento das funções mono-exponenciais. Matematicamente...

‣ Analysis of nuclear relaxation in granular systems

Rabbani,Said R.; Mendonça,Christovam; Mamani,J. B; Cervantes R.,Hernán
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2006 Português
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The longitudinal nuclear magnetic relaxation time, T1, of powdered samples was analyzed following the theory proposed by Browstein and Tarr to explain the T1 reduction of water confined in biological cells and the proposed by Rabbani and Edmonds where the molecular diffusion in liquids is substituted by spin diffusion to interpret the T1 behavior in solid particles. We have shown that the multiexponential character of magnetization decay in solid particles with a narrow band size distribution allows to evaluate the spin diffusion coefficient of this material. On the other hand if the diffusion coefficient of a material is given and the average size of a sample of this material is known the relaxation decay curve can be used to determine the surface relaxivity as well as the relative size of particles present in the other samples of same material. However, this analysis is unable to provide the absolut measurement of the grain sizes. Furthermore, it is shown that the grain geometry does not influence the relaxation decay curve.

‣ Distance estimates from paramagnetic enhancements of nuclear relaxation in linear and flexible model peptides.

Jacob, J; Baker, B; Bryant, R G; Cafiso, D S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1999 Português
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The distance dependence of electron-nuclear dipole-dipole coupling was tested using a series of poly-L-proline based peptides of different length. The poly-proline based peptides were synthesized with a nitroxide spin label on the N-terminus and a tryptophan on the C-terminus, and paramagnetic enhancements of nuclear spin-lattice relaxation rates were measured for the aromatic protons on the tryptophan as a function of the number of proline spacers in the sequence. As expected, paramagnetic enhancements decrease with distance, but the distances deduced from the NMR relaxation rates were shorter than expected for every peptide studied compared to a rigid linear poly-L-proline type II helix structure. Calculations of cross-relaxation rates indicate that this difference is not the result of spin-diffusion or the creation of a spin-temperature gradient in the proton spins caused by the nitroxide. Molecular dynamics simulations were used to estimate dynamically averaged value of (2). These weighted average distances were close to the experimentally determined distances, and suggest that molecular motion may account for differences between the rigid linear models and the distances implied by the NMR relaxation data. A poly-L-prolone peptide synthesized with a central glycine hinge showed dramatic relaxation rate enhancements compared to the peptide of the same length lacking the hinge. Molecular dynamics simulations for the hinged peptide support the notion that the NMR data is a representation of the weighted average distance...

‣ Nuclear Relaxation Time of Solid 3He: The Second and Fourth Moments of the Resonance Line

Matsumoto, Kazuyuki; Abe, Takayuki
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
Português
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This paper investigates the exchange narrowing of the nuclear relaxation time T1(0) of solid 3He at zero field. We obtain the theoretical expressions for T1(0) for both bcc and hcp 3He based on the multiple exchange models. It is found that the multiple exchange models for bcc 3He with two and/or three exchange parameters can explain the observed T1(0) data for a molar volume Vm = 24.2 cm3/mol.

‣ Fourth Moment Correction to the Spectral Density Responsible for the Longitudinal Nuclear Relaxation in Solid H2

Hama, Juichiro; Nakamura, Tuto
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
Português
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The spectral density responsible for the longitudinal nuclear relaxation time, T1, in solid H2 is studied at the high temperature limit of the rigid lattice, by taking the fourth moment into account. The relevant moments are evaluated simply by a systematic procedure based on the algebra of tensors, assuming the orientation dependent energy to be exclusively the electric quadrupole-quadrupole interaction. At high o-H2 concentration, the high temperature limit of T1 predicted by the present study is shorter than that by Gaussian approximation by about 10%, in agreement with the recent measurement by Amstutz et al., if one chooses the coupling constant of the quadrupole-quadrupole interaction to be consistent with other kinds of measurements.

‣ Nuclear magnetic resonance studies of structure and dynamics in heterogeneous samples; NMR studies of structure and dynamics in heterogeneous samples

Leu, Gabriela, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 143 leaves; 5318528 bytes; 5336783 bytes; application/pdf; application/pdf
Português
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The aim of this work is to develop and implement methods for determining the local structure and dynamics of heterogeneous samples (e.g. rocks, rubber, porous materials, etc.). From the physical point of view, the heterogeneities are best described in terms of variations in the local susceptibility. The proposed methods are based on analyzing the modulation of spin dynamics by the Magic Angle Sample Spinning (MASS) method in the presence of both local variations in the bulk magnetic susceptibility and molecular diffusion. The correlations between the dipolar and susceptibility fields are used for extracting information on the detailed structure and composition of heterogeneous samples. In the first part of this dissertation, a new method for characterizing porous media, diffusive MASS, is presented. This method is combining MASS and molecular diffusion, providing thus a unique way to simultaneously obtain high resolution spectra and information on the geometry and the internal fields inherent to porous samples. The second part is concerned with obtaining detailed information about the structure and dynamics in rubber samples with the aim of understanding the elastomer-carbon black interactions. The processes that occur at the elastomer-carbon black interface are responsible for the special properties that make rubber so useful and these processes are not yet fully understood. We use the dipolar and susceptibility interactions to characterize the elastomer spatial distribution relative to the carbon black surface...

‣ Spin-lattice relaxation of fluorine-19 in calcium fluoride at low temperatures

Day, Stephen Martin
Fonte: Universidade Rice Publicador: Universidade Rice
Português
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A study of nuclear relaxation due to paramagnetic impurities has been made, using the system of F19 nuclei in Ca F 2. T1 was measured at helium, hydrogen, and nitrogen temperatures. The field dependence of T1 at helium temperatures consists of three parts: at fields less than a few hundred gauss, the dependence of T1 on the field is parabolic; between a few hundred gauss and about 2.5 Kg, the dependence is linear; and at higher fields, it is linear, but has a steeper slope. Moreover, there is a strong orientation dependence in the helium range for a single crystal, and a size effect appears at higher fields. At temperatures above 14°K, T1 has only a weak orientation dependence. The experimental data indicate that T1 is minimum between 14°K and 63°K. An analysis of the experimental results with existing theories permits a determination of the field and temperature dependence of the relaxation time rho of the spin of the paramagnetic impurity. The analysis gives rho ∼ H-2T-1 for nitrogen and hydrogen temperatures. In the helium range, rho ∼ H-2 T-1 for Ho ≲ 2.5 Kg and rho ∼ H-1T-2 for Ho ≳ 2.5 Kg. rho is calculated to be ∼10-6 sec. at 14°K and the impurity concentration is calculated to be approximately one part in 106...

‣ Photon angular distribution and nuclear-state alignment in nuclear excitation by electron capture

Pálffy, Adriana; Harman, Zoltán; Surzhykov, Andrey; Jentschura, Ulrich D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/01/2007 Português
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The alignment of nuclear states resonantly formed in nuclear excitation by electron capture (NEEC) is studied by means of a density matrix technique. The vibrational excitations of the nucleus are described by a collective model and the electrons are treated in a relativistic framework. Formulas for the angular distribution of photons emitted in the nuclear relaxation are derived. We present numerical results for alignment parameters and photon angular distributions for a number of heavy elements in the case of E2 nuclear transitions. Our results are intended to help future experimental attempts to discern NEEC from radiative recombination, which is the dominant competing process.

‣ 1/T_1 nuclear relaxation time of \kappa-(BEDT-TTF)_ 2 Cu [N(CN)_2] Cl : effects of magnetic frustration

Hamad, I. J.; Trumper, A. E.; Wzietek, P.; Lefebvre, S.; Manuel, L. O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We study the role played by the magnetic frustration in the antiferromagnetic phase of the organic salt \kappa-(BEDT-TTF)_ 2 Cu [N(CN)_2] Cl. Using the spatially anisotropic triangular Heisenberg model we analyze previous and new performed NMR experiments. We compute the 1/T_1 relaxation time by means of the modified spin wave theory. The strong suppression of the nuclear relaxation time observed experimentally under varying pressure and magnetic field is qualitatively well reproduced by the model. Our results suggest the existence of a close relation between the effects of pressure and magnetic frustration.; Comment: 10 pages, 9 figures, to appear in Journal of Phys.: Condens Matter

‣ Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices

Tripathi, V.; Cooper, N. R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/06/2008 Português
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We propose a probe based on nuclear relaxation and Knight shift measurements for the Kondo scenario for the "0.7 feature" in semiconductor quantum point contact (QPC) devices. We show that the presence of a bound electron in the QPC would lead to a much higher rate of nuclear relaxation compared to nuclear relaxation through exchange of spin with conduction electrons. Furthermore, we show that the temperature dependence of this nuclear relaxation is very non-monotonic as opposed to the linear-T relaxation from coupling with conduction electrons. We present a qualitative analysis for the additional relaxation due to nuclear spin diffusion (NSD) and study the extent to which NSD affects the range of validity of our method. The conclusion is that nuclear relaxation, in combination with Knight shift measurements, can be used to verify whether the 0.7 feature is indeed due to the presence of a bound electron in the QPC.; Comment: Published version. Appears in a Special Section on the 0.7 Feature and Interactions in One-Dimensional Systems. 16 pages

‣ Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac: test for the theory of spin tunneling

Morello, Andrea; de Jongh, L. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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The description of the tunneling of a macroscopic variable in the presence of a bath of localized spins is a subject of great fundamental and practical interest, and is relevant for many solid-state qubit designs. Instead of focusing on the the "central spin" (as is most often done), here we present a detailed study of the dynamics of the nuclear spin bath in the Mn12-ac single-molecule magnet, probed by NMR experiments down to very low temperatures (T = 20 mK). We find that the longitudinal relaxation rate of the 55Mn nuclei in Mn12-ac becomes roughly T-independent below T = 0.8 K, and can be strongly suppressed with a longitudinal magnetic field. This is consistent with the nuclear relaxation being caused by quantum tunneling of the molecular spin, and we attribute the tunneling fluctuations to the minority of fast-relaxing molecules present in the sample. The transverse nuclear relaxation is also T-independent for T < 0.8 K, and can be explained qualitatively and quantitatively by the dipolar coupling between like nuclei in neighboring molecules. We also show that the isotopic substitution of 1H by 2H leads to a slower nuclear longitudinal relaxation, consistent with the decreased tunneling probability of the molecular spin. Finally...

‣ Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear Relaxation

Lazarian, A.; Hoang, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We consider grains with superparamagnetic inclusions and report two new condensed matter effects that can enhance the internal relaxation of the energy of a wobbling grain, namely, superparamagnetic Barnett relaxation, as well as, an increase of frequencies for which nuclear relaxation becomes important. This findings extends the range of grain sizes for which grains are thermally trapped, i.e. rotate thermally, in spite of the presence of uncompensated pinwheel torques. In addition, we show that the alignment of dust grains by radiative torques gets modified for superparamagnetic grains, with grains obtaining perfect alignment with respect to magnetic fields as soon as the grain gaseous randomization time gets larger than that of paramagnetic relaxation. The same conclusion is valid for the mechanical alignment of helical grains. If observations confirm that the degrees of alignment are higher than radiative torques can produce alone, this may be a proof of the presence of superparamagentic inclusions.; Comment: 5 pages, emulated ApJ style, 2 figures, submitted to ApJL (earlier version was corrupted)

‣ Identification of Nuclear Relaxation Processes in a Gapped Quantum Magnet: Proton NMR in the S=1/2 Heisenberg Ladder Cu2(C5H12N2)2Cl4

Chaboussant, G.; Julien, M. -H.; Fagot-Revurat, Y.; Levy, L. P.; Berthier, C.; Horvatic, M.; Piovesana, O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/06/1997 Português
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The proton hyperfine shift K and NMR relaxation rate $1/T_1$ have been measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap $\Delta \simeq J_\perp-J_\parallel$ in this strongly coupled ladder ($J_\parallel < J_\perp$) is supported by the K and $1/T_1$ results. By comparing $1/T_1$ at two different proton sites, we infer the evolution of the spectral functions $S_z(q,\omega_n)$ and $S_\perp(q,\omega_n)$. When the gap is significantly reduced by the magnetic field, two different channels of nuclear relaxation, specific to gapped antiferromagnets, are identified and are in agreement with theoretical predictions.; Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letters

‣ Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6

Morello, A.; Mettes, F. L.; Bakharev, O. N.; Brom, H. B.; Jongh, L. J. de; Luis, Fernando; Fernández, Julio F.; Aromí, Guillem
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 710146 bytes; application/pdf
Português
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17 pages, 11 figures, 1 appendix.-- PACS number(s): 75.10.Jm, 75.30.Kz, 76.60.-k; Few examples of magnetic systems displaying a transition to pure dipolar magnetic order are known to date. As was recently shown, within the newly discovered class of single-molecule magnets, quite attractive examples of dipolar magnetism may be found. The molecular cluster spins and thus their dipolar interaction energy can be quite high, leading to reasonably accessible ordering temperatures even for sizable intercluster distances. In favorable cases bonding between clusters in the molecular crystal is by van der Waals forces only, and no exchange paths of importance can be distinguished. An important restriction, however, is the requirement of sufficiently low crystal field anisotropy for the cluster spin, in order to prevent the occurrence of superparamagnetic blocking at temperatures above the dipolar ordering transition. This condition can be met for molecular clusters of sufficiently high symmetry, as for the Mn6 molecular cluster compound studied here. The uniaxial anisotropy of the cluster spin S=12 is as small as D/kB=0.013 K, giving a total zero-field splitting of the S=12 multiplet of 1.9 K. As a result, the electron-spin lattice relaxation time remains fast (~10–4 s) down to Tc and no blocking occurs. Magnetic specific heat and susceptibility experiments show a transition to ferromagnetic dipolar order at Tc=0.16 K. Classical Monte Carlo calculations...

‣ Preserving hyperpolarised nuclear spin order to study cancer metabolism

Marco-Rius, Irene
Fonte: University of Cambridge; Department of Biochemistry; Ftizwilliam College Publicador: University of Cambridge; Department of Biochemistry; Ftizwilliam College
Tipo: Thesis; doctoral; PhD
Português
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Monitoring the early responses of tumours to treatment is a crucial element in guiding therapy and increasing patient survival. To achieve this, we are using magnetic resonance imaging (MRI), which can provide detailed physiological information with relatively high temporal and spatial resolution. In combination with the dynamic nuclear polarisation (DNP) technique, high signal-to-noise is obtained, resulting in a powerful tool for in vivo 13C metabolic imaging. However, detection of hyperpolarised substrates is limited to a few seconds due to the exponential decay of the polarisation with the longitudinal relaxation time constant T1. This work aimed to improve the combination of hyperpolarisation and metabolic NMR/ MRI by extending the observation timescale of the technique. Working with quantum mechanical properties of the detected substrates, long lifetimes might be accessible by using the nuclear singlet configuration of two coupled nuclei. The singlet state is immune to intramolecular dipole-dipole relaxation processes, which is one of the main sources of signal decay in MRI. In favourable situations, the singlet relaxation time constant can be much longer than T1, so transfer of the polarisation into the singlet state may allow one to extend the usable time period of the nuclear hyperpolarisation. Here we studied the relaxation of hyperpolarised metabolites...