Academic literature on the topic 'Magnetic ac susceptibility'

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Journal articles on the topic "Magnetic ac susceptibility"

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Tanaka, Kazuyoshi, Tohru Sato, Kazunari Yoshizawa, Kenji Okahara, Tokio Yamabe, and Madoka Tokumoto. "ac magnetic susceptibility of TDAE-C60." Chemical Physics Letters 237, no. 1-2 (May 1995): 123–26. http://dx.doi.org/10.1016/0009-2614(95)00296-g.

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Nakane, Hiroyuki, Gaku Motoyama, Setsushi Nakamura, Takashi Nishioka, and Noriaki K. Sato. "AC magnetic susceptibility measurements on UGe2." Physica C: Superconductivity 388-389 (May 2003): 531–32. http://dx.doi.org/10.1016/s0921-4534(02)02660-6.

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Kimishima, Y., K. Inagaki, K. Tanabe, N. Nagata, and Y. Ichiyanagi. "AC magnetic susceptibility of Bi2223-system." Journal of Magnetism and Magnetic Materials 177-181 (January 1998): 547–48. http://dx.doi.org/10.1016/s0304-8853(97)00518-0.

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Mei, Yu, H. L. Luo, D. X. Chen, J. Nogues, and K. V. Rao. "ac magnetic susceptibility of YBa2Cu3O7−x." Journal of Applied Physics 64, no. 5 (September 1988): 2533–36. http://dx.doi.org/10.1063/1.341637.

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Chakravarti, A., R. Ranganathan, and A. K. Raychaudhuri. "An automated ac-magnetic susceptibility apparatus." Pramana 36, no. 2 (February 1991): 231–41. http://dx.doi.org/10.1007/bf02845708.

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Wurlitzer, M., M. Lorenz, K. Zimmer, and P. Esquinazi. "ac susceptibility of structuredYBa2Cu3O7thin films in transverse magnetic ac fields." Physical Review B 55, no. 17 (May 1, 1997): 11816–22. http://dx.doi.org/10.1103/physrevb.55.11816.

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Jin, X. C., Y. Y. Xue, Z. J. Huang, J. Bechtold, P. H. Hor, and C. W. Chu. "ac magnetic susceptibility of melt-texturedYBa2Cu3O7−δ." Physical Review B 47, no. 10 (March 1, 1993): 6082–85. http://dx.doi.org/10.1103/physrevb.47.6082.

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Klik, I., Y. D. Yao, X. Yan, and C. R. Chang. "Magnetic viscosity effect in ac susceptibility measurements." Physical Review B 57, no. 1 (January 1, 1998): 92–95. http://dx.doi.org/10.1103/physrevb.57.92.

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Mukherjee, S., R. Ranganathan, A. Chakravarti, and S. Sil. "AC susceptibility enhancement studies in magnetic systems." Journal of Magnetism and Magnetic Materials 224, no. 3 (2001): 210–20. http://dx.doi.org/10.1016/s0304-8853(00)01391-3.

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Mandache, S., A. Crisan, G. Aldica, and S. Popa. "Magnetic AC susceptibility in Bi2Sr2CaCu2O8 single crystals." Journal of Superconductivity 10, no. 3 (June 1997): 211–14. http://dx.doi.org/10.1007/bf02770553.

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Dissertations / Theses on the topic "Magnetic ac susceptibility"

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König, Tobias. "Probing magnetic Dynamics inNanoarrays using AC susceptibility." Thesis, Uppsala universitet, Materialfysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-415073.

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This project revised a magneto-optical ac susceptometer aiming to improve the experimentalapproach to investigate the magnetization dynamics of magnetic nano arrays.First the experimental setp was equipped with a new Helmholtzcoil which enables strongerAC magnetic eld compared to the installed coils on the system. That includes i.e. higherRMS magnetic eld amplitudes and a higher cut-o frequency in order to increase thefrequency range for magnetization dynamic measurements. Therefore dierent coil prototypeswere fabricated and tested in table top experiments using dierent additive manufacturingmethods, before the coil was installed on the cryostat and calibrated in thesoftware.In the second part of the project magnetization dynamics of nanostructures were studiedwith this new setup. As a rst step the general functionality of the Set-Up was testedusing a continuous ferromagnetic lm. Subsequently patterned circular discs were investigatedaiming to improve the calibration of the newly designed Helmholtzcoil. Startingfrom pattern with non coupled elements the project lastly investigated frequency dependentthermally active square articial spin ice (sASI), measuring freezing dynamics usingthe frequency dependent AC susceptometer.
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Salim, Maan. "The AC magnetic susceptibility of high temperature superconductors." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270233.

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Johnson, Ryan Christopher. "A study of the onset of magnetic correlations in LiY(1-x)Ho(x)F(4)." Thesis, Boston College, 2012. http://hdl.handle.net/2345/2596.

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Thesis advisor: Michael J. Graf
In this work I present a characterization of spin dynamics in LiY1-xHoxF4 over a wide region of frequency - temperature - magnetic field - concentration phase space to probe the onset of magnetic correlations. Specifically, measurements were made of the T = 1.8 K magnetic field and frequency dependence of AC susceptibility, and temperature and field dependence of the longitudinal field positive muon spin relaxation (μSR) for LiY1-xHoxF4 with x = 0.0017, 0.0085, 0.0408, and 0.0855. To determine the concentration range over which the spin dynamics are determined primarily by the Ho3+-μ interaction rather than by the F-μ interaction I characterize the dynamics associated with the formation of the (F-μ-F)−complex by comparing data with Monte Carlo simulations. Numerical simulations of the susceptibility for the x = 0.0017 and 0.0085 are fit to my data and show that Ho-Ho cross-relaxation processes become important at higher concentration, signaling the crossover from single-ion to correlated behavior. The muon spin depolarization is simulated using the parameters extracted from the susceptibility, and the simulations agree well with data for these two samples. It is found that the susceptibility and μSR data for samples with x = 0.0408 and 0.0855 cannot be described within a single-ion picture, possibly due to the onset of collective phenomena. An unusual peak is also discovered in the magnetic field dependence of the muon relaxation rate in the temperature interval 10 – 20 K, and ascribed to a modification of the Ho3+ fluctuation rate due to a field induced shift of the energy splitting between the ground and first excited doublet crystal field states relative to a peak in the phonon density of states centered near 63 cm-1
Thesis (PhD) — Boston College, 2012
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Souza, Ruberley Rodrigues de. "Susceptômetro para medidas automáticas da susceptibilidade magnpetica AC." Universidade de São Paulo, 1992. http://www.teses.usp.br/teses/disponiveis/54/54131/tde-14012009-104434/.

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Foi desenvolvido uma ponte de indutâncias mútuas, auto-balanceada, para medidas automáticas e simultâneas das partes real (x\') e imaginária (x\") da susceptibilidade magnética AC, na faixa de freqüências de 20 Hz e 1 KHz e temperaturas de 2K a 300K. O sistema é balanceado em um elo de realimentação digital que assegura um sinal, em fase e quadratura, continuamente nulo. A amplificação do sinal é feita através de um amplificador \"lock-in\" de duas fases, cujas saídas comandam dois DAC multiplicadores, gerando o sinal composto que é usado para balancear a ponte. O valor absoluto da susceptibilidade é medida movendo as bobinas primária e secundárias de tal forma que a amostra fique posicionada ora em um dos secundários, ora em outro. A resolução da parte numérica é 1 em 4000. A sensibilidade alcançada foi de 10-7 emu para amostras de 10-2cm-3 em um campo de excitação de amplitude 15 Gauss. A interface com um microcomputador ainda não foi desenvolvida.
An automatic self-balanced mutual inductance bridge has been designed to measure the real (x\') and imaginary (x\") parts of the magnetic AC susceptibility simultaneously in the frequency range 20 Hz to 1 KHz and temperatures between 2K to 30OK. The system is based on a digitally controlled feedback loop, which ensures continuous balanced operation, in phase as well in quadrature. The signal amplification chain is made of a dual-phase lock-in amplifier, whose outputs command two DAC multipliers, generating the composite balance signal for nulling the bridge. The absolute value of the susceptibility is measured by moving the primary and secondary coils in such a way to place the sample in the center of both secondary coils. The resolution of the numerical part is 1 in 4000. Sensivities of the order of 10-7 emu for samples of 10-2cm-3 in a primary field of 15 gauss have been obtained. The interface with a desktop computer has not been developed yet.
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Bracanovic, Darko. "Ac susceptibility and resistivity studies of YBa←2Cu←3O←7←-←#delta# high-temperature superconductors." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302027.

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Gomes, Rafael Cabreira. "Construção de um susceptômetro AC e a susceptibilidade magnética de microfios amorfos recobertos por vidro." Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/9206.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Glass covered microwires are materials with soft magnetic properties suitable to several technological applications, specially in magnetic sensors. The main feature of these wires, with negative magnetostriction, it is the magnetic domain structure, which are studied in several research centers. In this work it was developed an AC susceptometer capable to operate at room temperature at different applied fields and stress and another one to operate in cryogenic temperatures. The AC susceptibility technique carry out information either about the dynamic magnetic processes as the dissipative one that occur into the samples. In particular, microwires samples with nominal composition of Co68.25Fe4.25Si12.5B15 were studied. These Co-rich microwires exhibit the bamboo-like domain structure, meaning an axially magnetized core surrounded by a circumferentially magnetized shell. The AC susceptibility study on these samples give us information as, for example, that with the increase of the applies stress, there is an increase of the volume of the circumferentially magnetized shell at expenses of the inner core volume. It was also verified that, the magnetic behavior with the reduction of the temperature is similar to that observed when the microwires are axially stressed. This fact is due to the competition between the maganetoelastic and magnetostatic energies.
Microfios amorfos recobertos por vidro são materiais com propriedades magnéticas macias adequadas para várias aplicações tecnológicas, especialmente sensores magnéticos. Uma das principais características desses microfios com magnetostricção negativa é a sua estrutura de domínios magnéticos, que é alvo de diversos estudos em centros de pesquisa pelo mundo. Nesse trabalho foi desenvolvido e construído um susceptômetro para medidas de susceptibilidade magnética AC em temperatura ambiente e um outro para operar em temperaturas criogênicas. Para o caso de materiais magnéticos, a técnica de susceptibilidade AC traz informações de relevância sobre os processos de magnetização, como a dinâmica dos momentos magnéticos e processos dissipativos que ocorrem no interior da amostra. Em particular, foram estudadas amostras de microfios amorfos recobertos por vidro com composição nominal de Co68.25Fe4.25Si12.5B15. Esses microfios amorfos ricos em cobalto exibem uma estrutura de domínios magnéticos denominada como bamboo, estrutura essa que corresponde a um núcleo magnetizado longitudinalmente envolto por um domínios magnetizados circunferencialmente. O estudo da susceptibilidade magnética trouxe informações de relevância sobre essas amostras, onde conseguimos constatar principalmente que com o aumento da tensão mecânica externa, há um aumento volumétrico dos domínios com magnetização circunferencial as custas do volume do núcleo magnetizado axialmente. Verificou-se ainda com esse estudo, que esses microfios exibem um comportamento magnético em função da temperatura muito parecido com o comportamento magnético frente a tensão mecânica externa. Isso é fruto de uma competição entre as energias magnetoelástica e magnetostática, que são as principais energias envolvidas nesses materiais.
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Souza, Ruberley Rodrigues de. "Construção de um Susceptômetro AC Autobalanceado e Estudo de Polímeros Condutores Eletrônicos por Susceptibilidade Magnética e Ressonância Magnética." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-11092008-170555/.

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Neste trabalho, é descrito uma ponte de indutâncias mútuas que pode ser usada para medidas automáticas de susceptibilidade magnética AC, em freqüências até 1 kHz. Este susceptômetro utiliza um novo e alternativo arranjo para o \"probe\". O conjunto de bobinas, mantido em temperatura ambiente, é movimentado de tal forma a posicionar a amostra no centro de cada uma das bobinas secundárias. A amostra, cuja posição é fixa, tem sua temperatura controlada por um criostato de fluxo de Hélio. O acoplamento magnético do \"probe\" com materiais na vizinhança foi minimizado com o uso de uma blindagem magnética. Este \"probe\" tem uma sensibilidade de 10-7 emu com um campo magnético AC de 8 G rms e freqüência de 100 Hz. Neste trabalho, são apresentados também alguns resultados de susceptibilidade magnética AC, obtidos em supercondutores de alto Tc e compostos intermetálicos de terras raras. A relação entre transporte de cargas e propriedades magnéticas, de poliparafenileno (PPP) dopado com FeCl3 e poli(o-metoxianilina) (POMA) dopada com TFA e HCl, foi estudada utilizando as técnicas de Susceptibilidade Magnética AC (SMAC), Ressonância Paramagnética Eletrônica (RPE) e Ressonância Magnética Nuclear (RMN). Os resultados obtidos para o PPP foram interpretados em termos de três contribuições: presença do polaron paramagnético, cuja mobilidade aumenta com o aumento da temperatura; íons Fe3+ coordenados em sítios de baixa simetria da molécula FeCl3; e íons Fe3+ fortemente acoplados via interação de troca. A dependência com a temperatura do sinal de RPE da POMA pode ser entendido em termos da dinâmica dos polarons. O estreitamento da linha de RPE, devido a dopagem do material, pode ser explicada por dois processos diferentes. Em baixas temperaturas, predomina a interação de troca polaron-polaron, modulada pelas autuações de spin. Em altas temperaturas o \"motional narrowing\" é provocado pelo aumento de mobilidade do polaron. Em temperaturas intermediárias, é observado um efeito anômalo: a largura de linha cresce abruptamente, produzindo um pico em torno de 220 K. Este pico pode ser associado a contribuição não secular para a largura de linha. Acredita-se que o espalhamento do polaron por moléculas de oxigênio, promova um aumento no mecanismo de relaxação spin-rede. Os resultados de RMN para o 1H e 19F mostram que as componentes espectrais da largura de linha, são associadas com as fases amorfa e cristalina da POMA. Neste material, a taxa de relaxação spin-rede do 1H aumenta mais de uma ordem de grandeza com a dopagem. Isto pode ser explicado por um mecanismo de relaxação envolvendo acoplamento hiperfino núcleo-polaron.
A mutual inductance bridge which may be used for automatic measurement of ac magnetic susceptibilities from 4 K to room temperature, at frequencies up to 1 kHz, is described. The susceptometer employs an alternative and new arrangement for the probe. The coil set is kept at room temperature and moves in such a way to place the sample in the center of each of the secondary coils. The sample, motionless, has its temperature controlled by a helium flow refrigerator. Use of a magnetic shield minimizes coupling of the probe with nearby materials. This probe has a sensitivity of 10-7 emu in an ac magnetic field of 8G rms and frequency of 100 Hz. Typical results of ac magnetic susceptibility, obtained in high Tc, superconductors and rare earth intermetallic compounds are shown. AC Magnetic Susceptibility, Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) were used to study the relation between charge transport and magnetic properties of polyparaphenylene (PPP) doped with FeCl3 and poly(o-methoxyaniline) (POMA) doped with TFA and HCl. The results obtained in PPP can be interpreted in terms of three major contributions: the presence of the paramagnetic polaron, whose mobility increases with increasing temperature, Fe3+ ions coordinated in the low symmetry site of the FeCl3 molecule, and Fe3+ ions strongly coupled via exchange interaction. The temperature behavior of the EPR of POMA can be understood in terms of the dynamics of the polaron. Line narrowing, induced by doping the material, can be explained by two different processes. At low temperature, polarons are coupled via exchange interaction and the exchange narrowing of the line is caused by thermal spin fluctuations. At high temperature, motional narrowing is the most efficient mechanism. At intermediate temperatures, an anomalous effect is observed: linewidth increase abruptly, showing a peak at 220 K. This peak can be associated to the non-secular contribution to the line width. It is assumed that the spin-lattice relaxation mechanism is enhanced, at this temperature, due to the polaron scattering by paramagnetic oxygen molecules. 1H and 19F NMR data shows that the linewidth spectral components are associated with the amorphous and crystalline phases of the POMA. 1H spin-lattice relaxation rates, in this material, increases more than one order of magnitude after doping. This can be explained by a relaxation mechanism involving nucleus-polaron hyperfine coupling.
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Fischer, Giovana Zanini Gadioli 1980. "Propriedades magnéticas de filmes multicamadas Gd/W e Gd/Cr depositados por sputtering." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278273.

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Orientador: Marco Antonio Bica de Moraes
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Neste trabalho, a técnica de magnetron-sputtering foi empregada para fabricar filmes multicamadas de Gd/W e Gd/Cr, cujas propriedades magnéticas foram investigadas em função da espessura das camadas de Gd, dGd, e da temperatura do substrato, TS, durante a deposição. Espectroscopia de retroespalhamento Rutherford e espectroscopia fotoeletrônica de raios-x foram utilizadas, respectivamente, para detectar possível contaminação de oxigênio e para verificar a continuidade da camada de Gd sobre W e Cr. Difratometria de raios-X de baixo ângulo (GAXRD) e microscopia eletrônica de varredura (MEV) foram empregadas para investigar a estrutura cristalina e morfologia das amostras. As análises de GAXRD mostraram que nas amostras Gd/W as camadas de Gd são amorfas. Nas amostras Gd/Cr, entretanto, a cristalinidade do Gd aumenta com o aumento de dGd e TS. Pelas medidas de MEV foi visto que os filmes de Gd tanto sobre W quanto Cr são granulares. Para investigar as propriedades magnéticas utilizamos um magnetômetro SQUID e um PPMS. O primeiro foi utilizado para as medidas de momento magnético em função do campo estático, Hdc, e da temperatura, T. O PPMS foi utilizado nas investigações de susceptibilidade magnética ac em função de T, medidas em diferentes frequências de oscilação do campo e diferentes Hdc. A complexa natureza magnética dos filmes com dGd = 10 nm foi observada através das isotermas M x H, que não apresentaram saturação, para a maioria das amostras, nem mesmo em baixas temperaturas e altos campos. Pela análise dos dados magnéticos em função da temperatura, observamos que o caráter ferromagnético nas amostras se acentua à medida que TS e dGd aumentam. A temperatura de Curie, TC, também depende de TS e dGd, aumenta de 247 a 297 K com o aumento dos dois últimos parâmetros. A partir das isotermas M x H o momento magnético de saturação a 0 K foi calculado, e ele mostrou-se dependente de TS. A existência de vidros magnéticos nas amostras com dGd = 10 nm foi fortemente sugerida pelos resultados obtidos de magnetização e susceptibilidade ac, ambas em função de T. Para filmes com dGd = 10 nm, o efeito magnetocalórico foi investigado através da variação de entropia magnética, ?SM, em função da temperatura, para a remoção de um campo de 50 kOe. Curva de ?SM x T para as amostras Gd/Cr com TS = 300 e 500 ºC exibiram picos a alta temperatura denotando ferromagnetismo. Por outro lado, a amostra Gd/Cr depositada a 30ºC e todos os filme Gd/W não apresentaram nenhum pico em ?SM x T, indicando ausência ou baixa quantidade da fase ferromagnética. Todas as medidas são consistentes em indicar múltiplas fases magnéticas nas amostras e temperaturas de transição. Uma forte consistência entre as medidas magnéticas, GAXRD e MEV é verificada
Abstract: Direct current magnetron sputtering was used to synthetize Gd/W and Gd/Cr multilayer films, whose magnetic properties were investigated as a function of the Gd layer thickness, dGd, and the substrate temperature, TS, during deposition. Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy were employed, respectively, to detect possible oxygen contamination and to check the continuity of the coverage of the Gd layers on top of those of W and Cr. Grazing angle X-ray diffraction (GAXRD) and scanning electron microscopy (SEM) were used to investigate the crystalline structure and the morphology of the samples. The GAXRD analyses have shown that in the Gd/W samples the Gd layers are amorphous. In the Gd/Cr samples, however, Gd is crystalline. In these samples, the Gd crystalline order increases with increasing TS and dGd. From the SEM analysis, it was found that the Gd layers in either Gd/W or Gd/Cr samples were granular. To investigate the magnetic properties of the films, SQUID and PPMS magnetometries were used. With the former technique, the magnetic moments of the samples were measured as a function of a dc magnetic field, Hdc, and temperature, T. By PPMS, alternating magnetic fields, superimposed by different Hdc fields were used. The moments were measured as a function of T, Hdc and the frequency of the alternating field. The complex magnetic nature of the films with dGd = 10 nm was observed from the M x H isotherms, which did not show, for most of the samples, saturation even at high magnetic films and low temperatures. From the magnetic data as a function of temperature, it was observed that ferromagnetic character of the samples is enhanced as dGd and TS were increased. The Curie temperature, TC, also depends on TS and dGd as it increases from 247 to 297 K as the latter variables are increased. From the M x H isotherms the saturation magnetic moment at 0 K was determined, and it was observed that it depends on TS. The existence of magnetic glass states in samples with dGd = 10 nm was strongly suggested from both magnetization and ac susceptibility measurements as a function of T. For films with dGd = 10 nm, the magnetocaloric effect was investigated by the magnetic entropy change, ?SM, as a function of the temperature for the removal of a 50 kOe field. The ?SM x T plots for the Gd/Cr samples deposited at TS = 300 and 500 ºC exhibited high temperature peaks denoting ferromagnetism. On the other hand, for the Gd/Cr sample deposited at 30 ºC and for the all the Gd/W samples, such peaks were not seen, indicating the absence, or low-content, ferromagnetic phase. All magnetic measurements are consistent in indicating multiple magnetic phases in the samples and magnetic transition temperatures. A strong consistency among the magnetic and the GAXRD and SEM observations was also verified
Doutorado
Física da Matéria Condensada
Doutora em Ciências
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Rouxinol, Francisco Paulo Marques 1977. "Propriedades magnéticas de filmes de ligas GD-Cr." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278407.

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Orientador: Mario Antonio Bica de Moraes
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Técnicas de condensação de vapor são úteis na preparação de ligas magnéticas cujos componentes têm pouca, o mesmo nenhuma, solubilidade em condições de equilíbrio Neste trabalho, uma dessas técnicas ¿ sputtering ¿ foi empregada para fabricar ligas metaestáveis de GdXCr1-X, cujas propriedades magnéticas foram investigadas em função da concentração de Gd, x. Difratometria de raios-X de baixo ângulo (GAXRD) e espectroscopia de retroespalhamento Rutherford foram utilizados para determinar a estrutura do filme e sua composição elementar, respectivamente. As análises de GAXRD mostraram que a estrutura da fase de Gd, é hcp quando x ³ 0,88; e amorfa quando 0,16 £ 0,76. Uma estrutura bcc , para a fase de Cr, foi observada nos difratogramas quando x < 0,16, e amorfa quando x ³ 0,16 Para investigar as propriedades magnéticas utilizamos um magnetometro SQUID e m PPMS. O primeiro foi utilizado para as medidas de momento magnético em função do campo estático e temperatura. O PPMS foi tilizado nas investigações de susceptibilidade-AC em função da freqüência de oscilação do campo, temperatura e campo estático. A complexa natureza magnética dos filmes de Gd-Cr foi observada através das isotermas MxH, que não apresentaram saturação em baixas temperaturas, nem comportamento linear em altas temperaturas. Pela análise dos dados magnéticos, observamos que as amostras admitem um comportamento ferromagnético para x ³ 0,5 e paramagnético para as outras concentrações de Gd. A temperatura de Curie (TC) apresenta um aumento monotônico de 170 para 290 K quando x aumenta de 0,5 para 1,0. A temperatura de Curie-Weiss (q C) mostra um aumento monotônico com x. A partir das isotermas MxH a 2 K, o momento de saturação foi calculado, sendo independente de x e aproximadamente constante com um valor médio de 7,3 µB. Medidas de susceptibilidade em campos estáticos e dinâmicos revelaram a existência de comportamentos de vidros magnéticos em todas as amostras abaixo da temperat ra de freezing (Tf). Observamos, nas ligas com altas concentrações de Gd, a presença de comportamentos ferromagnéticos e cluster-glass em baixas temperaturas. Concluímos que a interação de troca entre os átomos de Gd dentro dos clusters de Gd não é do tipo RKKY, e sim do tipo supertroca. O efeito magnetocalórico (MCE) foi investigado através da variação de entropia magnética ( D SM) em função da temperatura, para a remoção de um campo de 50 kOe Curva de D SMxT para as amostras com x < 0,2 apresentaram um formato típico de superferromagneto, consistente com a existência de clusters Gd nos filmes. Nas outras amostras em que o EMC foi analisado, a presença de clusters é observada pelo comportamento dessas curvas a baixa temperatura; a altas temperaturas o comportamento de D SM com T indica fortemente a presença de mais fases magnéticas no filme. O diagrama de fase baseado em TC e Tf, e sua dependência com x é apresentado
Abstract: Vapor condensation techniques are very useful for preparation of alloys whose components have no mutual solubility under equilibrium conditions In this work, one of these techniques ¿ sputtering ¿ has been used to fabricate metastable GdXCr1-X alloys whose magnetic properties were investigated as a function of the Gd concentration, x. Grazing incidence angle X-ray diffraction (GAXRD) and Rutherford backscattering spectroscopy were employed to characterize the film structure and elemental composition, respectively. The GAXRD measurements revealed, for the Gd fraction, a hcp structure for x ³ 0,88; for 0,16 £ x £ 0,76 the Gd fraction was amorphous. The existence of a bcc structure for x < 0,16 was observed in the diffractograms for the Cr phase, which was amorphous for x ³ 0,16. To investigate the magnetic properties, a SQUID magnetometer and a PPMS were used. The former was employed for magnetic moment measurements as a function of applied static field and temperature. The PPMS was used for ac-susceptibility determinations as a function of the frequency of the ac driving field, temperature, and applied static field. The complex magnetic nature of the Gd-Cr films was revealed from the MxH isotherms which did not show saturation even at the lowest temperatures, and did not exhibit a linear behavior at higher temperatures. Processing of the magnetic data has shown that the films exhibit a ferromagnetic behavior for x ³ 0,5 and paramagnetic one for all other Gd concentrations. The Curie temperature (TC) increased monotonically from 170 to 290 K as x increased from 0,5 to 1,0. A monotonical increase in the Curie-Weiss temperature ( q C ) with x was also observed for all films. From the extrapolated MxH isotherm at 2 K (saturation magnetization), the saturation moments were calculated and found to be nearly constant at about 7.3 µB. Both static and dynamic susceptibility measurements revealed the existence of a magnetic glassy behavior in all alloys, occurring below a freezing temperature Tf . For the higher concentration alloys, the ferromagnetic and the cluster glass state were observed at low temperatures. It was thus concluded that the exchange interactions within Gd atoms in the clusters were not of the RKKY but of the superexchange type. The magnetocaloric effect (MCE) was investigated from the magnetic entropy change ( DSM) as a function of temperature, for the removal of a 50 kOe field. Samples with x < 0,2 exhibited DSMxT curves whose shapes are typical of a superferromagnet, consistently with the existence of Gd clusters in the films. For all the other alloys whose MCE was investigated, the presence of clusters is manifested from the behavior of these curves at low temperatures; at higher temperatures, the evolution of DSM with T strongly indicated the presence of more than one magnetic phase in the alloys A magnetic phase diagram based on the Tf and Tc transition temperatures and their dependence on x is presented in this thesis
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Westerkamp, Tanja. "Quantenphasenübergänge in den Schwere-Fermionen-Systemen Yb(Rh_{1-x}M_x)_2Si_2 und CePd_{1-x}Rh_x." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244202394324-81635.

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Die Betrachtung von Schwere-Fermionen-Systemen stellt ein wichtiges Themengebiet im Bereich der Festkörperphysik dar. Das Verhalten von Schwere-Fermionen-Systemen wird durch die starken Korrelationen der magnetischen Momente der ungepaarten Spins der f-Elektronen bestimmt. Experimentell zugängliche Messgrößen sind dadurch bei tiefen Temperaturen stark erhöht, so dass sich diese Systeme besonders gut zur Untersuchung von Grundzustandseigenschaften eignen. Zentrales Thema dieser Arbeit ist die Untersuchung zweier intermetallischer Seltenerd-Verbindungen in Bezug auf Quantenphasenübergänge. Diese treten am absoluten Nullpunkt der Temperatur als Funktion eines anderen Parameters wie Magnetfeld, Druck oder chemischer Substitution auf und sind bei endlicher Temperatur durch Abweichungen physikalischer Messgrößen von der durch L. D. Landau aufgestellten Theorie der Fermi-Flüssigkeiten nachzuweisen. Zu diesem Zweck wurden Tieftemperaturexperimente bis hinab zu 20mK und in Magnetfeldern bis zu 18T durchgeführt. Es wurden elektrischer Widerstand, magnetische Wechselfeldsuszeptibilität, Magnetostriktion und thermische Ausdehnung gemessen
The investigation of heavy-fermion systems marks an important subject in the research field of solid state physics. The behaviour of heavy-fermion systems is dominated by the strong correlations of the magnetic moments of the unpaired f-electron spins. At low temperatures, experimentally accessible variables are strongly enhanced so that these systems are especially suited to analyse ground state properties. The central topic of this thesis is the investigation of two intermetallic rare-earth compounds with regard to quantum phase transitions. The latter occur at zero temperature as a function of parameters such as magnetic field, pressure or chemical substitution. They are traceable at finite temperature due to deviations of physical variables from the theory of Fermi liquids established by L. D. Landau. For this purpose, low-temperature experiments were performed down to 20mK and in magnetic fields up to 18T. Electrical resistivity, magnetic ac susceptibility, magnetostriction and thermal expansion were measured
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Books on the topic "Magnetic ac susceptibility"

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Mørup, Steen, Cathrine Frandsen, and Mikkel F. Hansen. Magnetic properties of nanoparticles. Edited by A. V. Narlikar and Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533053.013.20.

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This article discusses the magnetic properties of nanoparticles. It first considers magnetic domains and the critical size for single-domain behavior of magnetic nanoparticles before providing an overview of magnetic anisotropy in nanoparticles. It then examines magnetic dynamics in nanoparticles, with particular emphasis on superparamagnetic relaxation and the use of Mössbauer spectroscopy, dc magnetization measurements, and ac susceptibility measurements for studies of superparamagnetic relaxation. It also describes magnetic dynamics below the blocking temperature, magnetic interactions between nanoparticles, and fluctuations of the magnetization directions. Finally, it analyzes the magnetic structure of nanoparticles, focusing on magnetic phase transitions and surface effects, non-collinear spin structures, and magnetic moments of antiferromagnetic nanoparticles.
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Book chapters on the topic "Magnetic ac susceptibility"

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Troć, R. "UTe: AC Magnetic Susceptibility." In Actinide Monochalcogenides, 946–49. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-47043-4_202.

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Troć, R. "U(P, S): AC Magnetic Susceptibility." In Actinide Monochalcogenides, 615–18. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-47043-4_106.

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Troć, R. "U(Sb, Te): AC Magnetic Susceptibility." In Actinide Monochalcogenides, 1030–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-540-47043-4_223.

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Williams, Gwyn. "AC Susceptibility of Dilute Magnetic Systems." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 475–502. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_26.

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Kuroda, Naoshi, and Ryozo Yoshizaki. "AC Magnetic Susceptibility of Bi2Sr2CaCu2O8 Single Crystal." In Advances in Superconductivity VII, 535–38. Tokyo: Springer Japan, 1995. http://dx.doi.org/10.1007/978-4-431-68535-7_119.

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Marohnić, Željko, and Emil Babić. "Critical Current Densities from ac Susceptibility Data." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 267–87. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_13.

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Clem, John R. "Ac Losses in Type-II Superconductors." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 177–211. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_8.

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Claassen, J. H. "AC Susceptibility Techniques Applied to Thin Film Superconductors." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 405–22. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_21.

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Schilling, J. S., J. Diederichs, S. Klotz, and R. Sieburger. "Ac Susceptibility Studies of Superconducting Properties Under High Hydrostatic Pressure." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 107–28. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_5.

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Salas, Francisco H. "Novel Low Field ac Magnetic Susceptibility Technique in UHV: Magnetism of hcp Gd(0001)." In Magnetic Susceptibility of Superconductors and Other Spin Systems, 519–29. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4899-2379-0_28.

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Conference papers on the topic "Magnetic ac susceptibility"

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Li, X., S. Dong, T. Yoo, X. Liu, M. Dobrowolska, and J. K. Furdyna. "Anisotropic ac magnetic susceptibility in (Ga, Mn)As film." In 2015 IEEE International Magnetics Conference (INTERMAG). IEEE, 2015. http://dx.doi.org/10.1109/intmag.2015.7156853.

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Kawabata, Ryuzo, Takako Mizoguchi, Akira Tsukamoto, Tomoko Yoshimura, Akihiko Kandori, and Keiji Enpuku. "Immunoassay detection without washing by using AC magnetic susceptibility." In 2010 Ninth IEEE Sensors Conference (SENSORS 2010). IEEE, 2010. http://dx.doi.org/10.1109/icsens.2010.5690049.

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Yin, Kuanrui, Dongxu Yang, Xiangchen Jia, and Ming Wang. "Study on Magnetic Particle Relaxation Detection Device Based on AC Magnetic Susceptibility." In ICITEE-2019: 2nd International Conference on Information Technologies and Electrical Engineering. New York, NY, USA: ACM, 2019. http://dx.doi.org/10.1145/3386415.3386980.

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Elrefai, A. L., T. Sasayama, T. Yoshida, and K. Enpuku. "Magnetic core-size distribution of magnetic nanoparticles estimated from magnetization, AC susceptibility and relaxation measurements." In 2017 IEEE International Magnetics Conference (INTERMAG). IEEE, 2017. http://dx.doi.org/10.1109/intmag.2017.8007882.

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Shigeoka, Daiki, Hikaru Katayanagi, Yuki Moro, Shinji Kimura, Toshiyuki Mashino, Tomoyuki Hiroki, and Yuko Ichiyanagi. "AC magnetic susceptibility of Co-Ti-Zn ferrite nanoparticles for hyperthermia agents." In 2010 IEEE 3rd International Nanoelectronics Conference (INEC). IEEE, 2010. http://dx.doi.org/10.1109/inec.2010.5425140.

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Hong, Chin-Yih, Shieh-Yueh Yang, Herng-Er Horng, Jen-Jie Chieh, and Hong-Chang Yang. "Universal Behavior for Characteristic Curve of Immunomagnetic Reduction Assay With Aid of Biofunctionalized Magnetic Nanoparticles." In ASME 2009 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/detc2009-86436.

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By biofunctionalizing magnetic nanoparticles with bioprobes, magnetic nanoparticles are able to specifically label bio-molecules. With the association between magnetic nanoparticles and bio-molecules, the mixed-frequency AC magnetic susceptibility generated with the physical rotation of individual magnetic nanoparticles under external AC magnetic fields is reduced. This detection technology is so-called immunomagnetic reduction (IMR) assay. In the experiment, several kinds of proteins and small-molecule chemicals were detected via IMR. The characteristic curves, i.e. the reduction versus the concentration of protein/chemical, for these proteins or chemicals can be scaled to one universal curve.
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Stoyanova-Ivanova, A., S. Terzieva, V. Mihailov, V. Mikli, and V. Kovachev. "AC Magnetic Susceptibility Of Elements In Ag Sheathed BSCCO (2223) Tapes With Te Addition." In SIXTH INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION. AIP, 2007. http://dx.doi.org/10.1063/1.2733543.

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Ludwig, Frank, Urs Häfeli, Wolfgang Schütt, and Maciej Zborowski. "Characterization of Magnetic Core-Shell Nanoparticle Suspensions Using AC Susceptibility for Frequencies up to 1 MHz." In 8TH INTERNATIONAL CONFERENCE ON THE SCIENTIFIC AND CLINICAL APPLICATIONS OF MAGNETIC CARRIERS. AIP, 2010. http://dx.doi.org/10.1063/1.3530020.

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Kumar, Punith V., M. R. Manju, and Vijaylakshmi Dayal. "Investigation of magnetic spin glass property in La0.5Bi0.5MnO3 sample using non-linear AC susceptibility measurements." In SOLID STATE PHYSICS: Proceedings of the 58th DAE Solid State Physics Symposium 2013. AIP Publishing LLC, 2014. http://dx.doi.org/10.1063/1.4873028.

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Ermakov, Alexey, Alexander V. Korolev, Waldemar Singer, and Xenia Singer. "A New Approach for RRR Determination of Niobium Single Crystal Based on AC Magnetic Susceptibility." In FIRST INTERNATIONAL SYMPOSIUM ON THE SUPERCONDUCTING SCIENCE AND TECHNOLOGY OF INGOT NIOBIUM. AIP, 2011. http://dx.doi.org/10.1063/1.3579236.

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