Página 1 dos resultados de 5643 itens digitais encontrados em 0.021 segundos

Ion dependence of magnetic anisotropy in MFe(2)O(4) (M = Fe, Co, Mn) nanoparticles synthesized by high-temperature reaction

Arelaro, Amanda Defendi; Lima Junior, Enio; Rossi, Liane Marcia; Kiyohara, Pedro Kunihiko; Rechenberg, Hercilio Rodolfo
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.14%
The influence of different M(2+) cations on the effective magnetic anisotropy of systems composed of MFe(2)O(4) (M Fe, Co and Mn) nanoparticles was investigated. Samples were prepared by the high-temperature (538 K) solution phase reaction of Fe (acac) 3, Co (acac) 2 and Mn (acac) 2 with 1,2 octanodiol in the presence of oleic acid and oleylamine. The final particles are coated by an organic layer of oleic acid that prevents agglomeration. Transmission electron microscopy (TEM) images show that particles present near spherical form and a narrow grain size distribution, with mean diameters in the range of 4.5 - 7.6 nm. Powder samples were analyzed by ac susceptibility and Mossbauer measurements, and K(eff) for all samples was evaluated using both techniques, showing a strong dependence on the nature of the divalent cation. (C) 2008 Elsevier B.V. All rights reserved.

Ruído magnético de Barkhausen contínuo rotacional.; Continuous rotational magnetic Barkhausen noise.

Caldas Morgan, Manuel Alfredo
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 10/05/2013 PT
Relevância na Pesquisa
56.41%
Este trabalho apresenta os avanços no desenvolvimento de um novo método de ensaio não-destrutivo magnético. O método está baseado na técnica do Ruído Magnético de Barkhausen (RMB), particularmente em uma variante denominada Barkhausen Contínuo. O RMB é gerado devido à ação de um campo magnético variável magnetizante que produz mudanças abruptas e irreversíveis na estrutura magnética do material. Essas mudanças são influenciadas pela microestrutura e a distribuição de tensões dentro do mesmo. As medições podem ser usadas para construir uma distribuição bidimensional do RMB ao redor de um ponto fixo, cujo resultado irá refletir o nível de anisotropia magnética, usualmente indicando um eixo de fácil magnetização, parâmetro relevante dado que o comportamento da grande maioria de materiais ferromagnéticos de engenharia é usualmente anisotrópico. As mudanças no eixo de fácil magnetização podem indicar a presença de anomalias mecânicas ou abnormalidades no processo de fabricação e no caso da aplicação de uma tensão externa, podem refletir a magnitude e a direção da mesma. O presente trabalho descreve uma metodologia que faz uso de um campo magnético rotacional para obter sinais RMB relacionados ao angulo de giro...

Evaluation of the anisotropy field for fine-particle systems from low-field thermomagnetic curves

Geshev, Julian Penkov; Martinez, Lluiz Martinez; Muñoz, Juan Santiago; Schmidt, Joao Edgar; Mikhov, Mihail
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
Relevância na Pesquisa
56.22%
A method for evaluating the temperaturedependent magnetic anisotropy field from thermomagnetic curves for Stoner–Wohlfarth-like systems is proposed. It allows the anisotropy parameters of a sample with unknown spontaneous magnetization to be obtained by using magnetic fields considerably lower than the anisotropy field.

Propriedades estruturais e magnéticas de nanofios de Ni e Co; Structural and magnetic properties in arrays of Ni and Co nanowires

Elvis Lira da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/03/2006 PT
Relevância na Pesquisa
56.35%
Os arranjos de nanofios magnéticos tem atraído um interesse considerável da comunidade científica, motivado principalmente pela sua utilização como sistemas-modelo e na possível aplicação em mídias magnéticas de alta densidade de informação. O comportamento magnético macroscópico desses sistemas é fortemente dependente das anisotropias magnéticas efetivas (determinadas principalmente pelas contribuições das anisotropias de forma, magnetocristalina e magnetoelástica). Neste trabalho realizamos um estudo completo das propriedades magnéticas de nanofios magnéticos de Ni e Co, variando o comprimento dos nanofios e a temperatura das amostras. Os nanofios são obtidos por eletrodeposição em nanoporos de membranas de alumina preparadas por um duplo processo de anodização em substratos de alumínio. A caracterização estrutural dos nanofios foi feita por microscopia eletrônica de varredura de alta resolução e microscopia de força magnética e revela que os arranjos de nanofios estão organizados em uma rede hexagonal onde possuem diametros de aproximadamente 35 nm e a distância entre os nanofios de aproximadamente 105 nm. O comprimento dos nanofios varia de aproximadamente 560 nm até 2250 nm. Observamos uma mudança do eixo fácil de magnetização da direção paralela ao eixo dos nanofios na temperatura ambiente para direção perpendicular ao eixo dos nanofios em baixas temperaturas. Analisamos a dependência da remanência reduzida e da coercividade em relação à temperatura e verificamos que as amostras apresentam uma temperatura de cruzamento entre as remanências reduzidas com campo aplicado paralela e perpendicularmente ao eixo dos nanofios...

Propriedades estruturais e magnéticas de nanofios de Co eletrodepositados; Structural and magnetic properties of electrodeposited Co nanowires

Peterson Grandini de Carvalho
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/09/2013 PT
Relevância na Pesquisa
56.41%
Redes de nanofios (NF) magnéticos têm atraído muita atenção devido suas possíveis aplicações tecnológicas. Do ponto de vista tecnológico tais redes poderiam ser utilizadas em diversas aplicações tais como dispositivos spintrônicos, sistemas de armazenamento de memória magnética, elementos sensores de campo magnético e em diversas aplicações biológicas. Por outro lado, do ponto de vista da ciência de base é fundamental compreender o efeito da baixa dimensionalidade nas propriedades magnéticas dos materiais. Muitas das propriedades magnéticas dos NF decorrem simplesmente de sua geometria. Neles, há uma forte anisotropia magnética de forma que tende a manter os momentos magnéticos alinhados ao eixo principal dos NF. No cobalto com estrutura hexagonal compacta (hcp), os momentos magnéticos tendem a se alinhar em uma direção cristalina preferencial (eixo c), ou seja, há uma anisotropia magnetocristalina. Tal anisotropia é da mesma ordem de grandeza da anisotropia de forma de NF ideias (cujo comprimento é muito maior que o diâmetro). Nanofios de cobalto hcp são interessantes basicamente porque suas propriedades magnéticas dependerão fortemente da estrutura cristalina (tamanho do grão e orientação do cristal em relação ao eixo principal dos nanofios). Como as duas contribuições de anisotropia são da mesma ordem de grandeza...

Magnetostricção e Anisotropia Magnética de filmes de Cobalto em substratos de vidro e silício; Magnetostricção and magnetic anisotropy of cobalt films on glass substrates and silicon

SÁ, Luciano Vaz de
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Física; Ciências Exatas e da Terra Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Física; Ciências Exatas e da Terra
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
66.25%
The Ferromagnetic Resonance technique is used to study the magnetostriction and the magnetic anisotropy of cobalt thin films grown on glass and silicon substrates. The effective values of the magnetostriction and magnetic anisotropy constants obtained do not agree with known values in the literature, but show the viability of the experimental method used [with the film glued to a cantilever beam under stress] to study the magnetostriction of magnetic thin films.; Este trabalho tem como objetivo estudar a magnetostricção e a anisotropia magnética de filmes finos de cobalto usando a técnica de Ressonância Ferromagnética. As amostras investigadas foram produzidas pela técnica de magnetron sputtering, depositadas sobre substratos de vidro e silício, com espessuras variando na faixa de 10 a 20 nm. Os valores efetivos obtidos para as constantes de magnetostricção e de anisotropia magnética de volume e de superfície diferem de valores conhecidos na literatura, mas comprovam a viabilidade do procedimento experimental aplicado [com o filme fixo sobre uma haste cantilever sujeita a stress] para investigar a magnetostricção de filmes finos magnéticos.

Anisotropia magnética em filmes epitaxiais Fe/Mn, Fe/Mn/Fe e Fe/Mn/Co; Magnetic anisiotropy in epitaxial filmsFe/Mn, Fe/Mn/Fe e Fe/Mn/Co

Pessoa, Márcio Solino
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG)
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
56.33%
This work reports the study of magnetic anisotropy of Fe/Mn bilayers, and Fe/Mn/Fe and Fe/Mn/Co trilayers, grown by molecular beam epitaxy onto monocrystalline MgO(001) substrates. Samples were produced with the Fe layer grown at a temperature of 175 ° C, with a thickness of 5 or 10 nm, the Co layer grown at 50 ° C, with a thickness of 2 or 5 nm, and the Mn layer grown at temperatures of 50 ° C, 150 ° C or 175 ° C, with thicknesses in the range from 0.80 to 2.20 nm. The angular variations of the in-plane absorption field, at Q-band (33.9 Ghz) microwave frequency, reveal the presence of a large four-fold magnetic anisotropy in all studied films. In samples with thicker Mn layers, two uniform resonance modes of bcc-Fe and bcc-Co layers are excited by the microwave field. The angular variations of the in-plane absorption field reveal for both layers the presence of fourth order cubic magnetic anisotropy. Films with the Mn layer thickness exceeding 1.16 nm exhibits, however, only a single absorption mode due to the overlapping of Fe-bcc and Co-bcc uniform resonance modes. Experiments at X-band (9.4 GHz) microwave frequency reveal the excitation of non-aligned and non-resonant modes, suggesting, for samples with the Mn layer grown at low temperature...

Anisotropia magnética em tricamadas epitaxiais Fe/Mn/Fe; Magnetic anisotropy Fe/Mn/Fe trilayers

Pessoa, Marcio Solino
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG)
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
66.34%
The ferromagnetic resonance (FMR) technique at the microwave frequencies of X-band (9.79 GHz) and Q-band (34 Ghz) was used to study, at room temperature, the magnetic anisotropy of Fe/Mn/Fe trilayers. The samples studied were grown by molecular beam epitaxy onto MgO substrates at the temperatures of 50 ° C, 150 ° C and 175 ° C, at the pressure of 4 x 10-11 Torr. The thicknesses of the distinct layers were 5 or 10 nm for the bottom Fe layer grown onto the MgO substrate, varied from 0.8 to 1.35 nm, for the Mn spacer layer, and was kept constant and equal to 5 nm, for the top Fe layer. The FMR spectra of the symmetrical trilayer at X and Q-band microwave frequencies show only the uniform resonance mode. Asymmetrical trilayers also show non resonant and/or non aligned modes at X-band frequency, but only the uniform mode at Q-band frequency. For some samples this result gives evidence of a non-collinear coupling between the Fe layers in the presence of low intensity magnetic fields. The out-of-plane angular dependence of the absorption fields show that the magnetization for all trilayers studied is in the plane of the sample. The magnetic anisotropy was deduced from the in-plane angular dependence of the uniform resonance mode at Q-band frequency...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.24%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Enhancement of the magnetic anisotropy of Co clusters by Au capping

Luis, Fernando; Bartolomé, Juan; Bartolomé, Fernando; Martínez Pérez, M. J.; García, L. M.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 10752 bytes; application/octet-stream
ENG
Relevância na Pesquisa
66.25%
et al.; We study the magnetic properties of Co nanoparticles, prepared by sputtering, with diameters ranging from 1 to 3.5 nm. The effective anisotropy, which determines the activation energy for the magnetization reversal, increases with decreasing particle's size, showing the dominant role played by surface atoms. We find that the superparamagnetic blocking temperature and the coercive field are significatively enhanced when the clusters are capped by a thin Au layer. This enhancement is probably caused by the bonding or hybridization of Co and Au atoms at the interface between the two metals. It provides thus a method to modify the magnetic anisotropy, which can be of interest for the applications of magnetic nanoparticles.; Peer reviewed

Magnetic properties of ultrathin FexCo(1-x) films on Pt(111)

Moulas, Géraud; Lehnert, Anne; Rusponi, S.; Zabloudil, J.; Etz, C.; Ouazi, S.; Etzkorn, Markus; Bencok, Peter; Gambardella, Pietro; Weinberger, P.; Brune, H.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 950086 bytes; application/pdf
ENG
Relevância na Pesquisa
56.24%
14 pages, 14 figures.-- PACS nrs.: 75.70.Ak; 75.30.Gw; 73.20.At.; The magnetism of 1-ML-thick films of Fe(x)Co(1−x) on Pt(111) was investigated both experimentally, by x-ray magnetic circular dichroism and magneto-optical Kerr effect measurements, and theoretically, by first-principles electronic structure calculations, as a function of the film chemical composition. The calculated Fe and Co spin moments are only weakly dependent on the composition and close to 3µ(B)/atom and 2µ(B)/atom, respectively. This trend is also seen in the experimental data, except for pure Fe, where an effective spin moment of only Seff=(1.2 ± 0.2) µ(B)/atom was measured. On the other hand, both the orbital moment and the magnetic anisotropy energy show a strong composition dependence with maxima close to the Fe(0.5)Co(0.5) stoichiometry. The experiment, in agreement with theory, gives a maximum magnetic anisotropy energy of 0.5 meV/atom, which is more than 2 orders of magnitude larger than the value observed in bulk bcc FeCo and close to that observed for the L10 phase of FePt. The calculations clearly demonstrate that this composition dependence is the result of a fine tuning in the occupation number of the d(x^2−y^2) and d(xy) orbitals due to the Fe-Co electronic hybridization.; Financial support from the Swiss National Science Foundation (Grants No. 200020- 109800 and No. 200020-112322) and from the Austrian Science Fund (FWF) within the Joint Research Programme S90 are gratefully acknowledged. Financial support of this work was also provided by the Austrian Science Foundation (Grant No. WK W004) and Oak Ridge National Laboratory (Subcontracts No. 4000043271 and No. 4000063148). We acknowledge the ESRF for provision of beam time and financial support from the EUROCORES 05-SONS-FP-009 SANMAG project of the European Science Foundation.; Peer reviewed

Control of the perpendicular magnetic anisotropy of FePd films via Pd capping deposition

Clavero Pérez, César; Skuza, J. R.; Choi, Y.; Haskel, D.; García-Martín, José Miguel; Cebollada, Alfonso; Lukaszew, R. A.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 464633 bytes; application/pdf
ENG
Relevância na Pesquisa
66.36%
We have investigated the influence of two capping layers (MgO and Pd) on the magnetic anisotropy of highly anisotropic L10 FePd films. While we mainly found perpendicular magnetic anisotropy in MgO capped films, we observed that the Pd capping layer induces formation of an additional new phase near the FePd/Pd interface that exhibits in-plane magnetic anisotropy. The combined effect of these two anisotropies results in global canted magnetic anisotropy. Thus, our findings illustrate a mechanism to influence the magnetic anisotropy in FePd highly ordered alloys via adequate choice of capping layer materials.; Peer reviewed

Perpendicular magnetic anisotropy in chemically disordered FePd–FeV(100) alloy thin films

Clavero Pérez, César; García-Martín, José Miguel; Armelles Reig, Gaspar; Cebollada, Alfonso; Huttel, Yves; Stradé, S.; Arbiol, J.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 613827 bytes; application/pdf
ENG
Relevância na Pesquisa
66.17%
We find that the use of V(100) buffer layers on MgO(001) substrates for the epitaxy of FePd binary alloys yields to the formation at intermediate and high deposition temperatures of a FePd–FeV mixed phase due to strong V diffusion accompanied by a loss of layer continuity and strong increase of its mosaic spread. Contrary to what is usually found in this kind of systems, these mixed phase structures exhibit perpendicular magnetic anisotropy (PMA) which is not correlated with the presence of chemical order, almost totally absent in all the fabricated structures, even at deposition temperatures where it is usually obtained with other buffer layers. Thus the observed PMA can be ascribed to the V interdiffusion and the formation of a FeV alloy, being the global sample saturation magnetization also reduced.; This work was partially financed by the Spanish Commission of Science and Technology and Comunidad de Madrid. One of the authors (C.C.) acknowledges the Ministerio de Educación y Ciencia and FPI program for financial support. Two of the authors (J.M.G.-M. and Y.H.) acknowledge the Consejo Superior de Investigaciones Científicas (CSIC) and Ramón y Cajal program for financial support. The authors thank Dr. Elisa Román for the use of the XPS equipment and fruitful discussions.; Peer reviewed

Order and phase nucleation in nonequilibrium nanocomposite Fe-Pt thin films with perpendicular magnetic anisotropy

Clavero Pérez, César; Skuza, J. R.; García-Martín, José Miguel; Cebollada, Alfonso; Walko, D. A.; Lukaszew, R. A.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 351791 bytes; application/pdf
ENG
Relevância na Pesquisa
66.21%
We report on the time evolution of mass transport upon annealing nonequilibrium Fe-Pt nanocomposite films, leading to nucleation of L10 chemically ordered phase. The nonequilibrium nanocomposite films were fabricated by applying Fe+ ion implantation to epitaxial Pt films grown on (001) MgO substrates, yielding Fe nanoclusters embedded in a Pt matrix at a tailored penetration depth. Time-resolved x-ray diffraction studies were carried out using synchrotron radiation, allowing determination of the activation energy for nucleation of the FePt L10 phase within the segregated nanoclusters during annealing. The growth of the segregated L10 ordered phase was modeled using ideal grain-size law and found to be dominated by strain-driven surface nucleation. The activation energies were found to correlate with the nanocluster size. Magnetic characterization of selected annealed samples indicates perpendicular magnetic anisotropy with high coercive field coincident with high value of the chemical order parameter of the ordered phase within the magnetic nanoclusters.; Funding from NSF (Grant No. DMR-0355171), Research Corporation Cottrell Scholar Award, and the American Chemical Society under Grant No. PRF-41319-AC10 is acknowledged. Funding from different Spanish Institutions...

Temperature and thickness dependence at the onset of perpendicular magnetic anisotropy in FePd thin films sputtered on MgO(001)

Clavero Pérez, César; García-Martín, José Miguel; Costa Krämer, José Luis; Armelles Reig, Gaspar; Cebollada, Alfonso; Huttel, Yves; Lukaszew, R. A.; Kellock, A. J.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 427499 bytes; application/pdf
ENG
Relevância na Pesquisa
66.31%
The onset of chemical order (L10 phase) and perpendicular magnetic anisotropy in FePd(001) thin films sputtered on MgO(001) at temperatures from room temperature to 700 °C and thickness between 1.4 and 22 nm are investigated. It is found that the formation of the FePd ordered phase exhibiting high perpendicular magnetic anisotropy (L10 phase with the c axis in the growth direction) is affected by a two-dimensional to three-dimensional growth mode transition with increasing deposition temperatures, hindering higher chemical ordering at moderate and high temperatures. For 22-nm-thick films, the ordered phase is only obtained in a narrow range of growth temperature centered at 450 °C. This fact, together with strong surface morphology dependence on the deposition temperature, determines the magnetic and magneto-optical properties of the studied system. No dependence of the ordering degree on film thickness is found for films with thicknesses of 3, 7 and 22 nm grown at 450 °C, with a constant value indicating that chemical ordering occurs since the early stages of growth and does not improve as the growth proceeds. The samples consist of chemically ordered nanostructures that range in size from 30 to 200 nm average diameter and 0.5–30 nm height as the film becomes thicker...

Magnetic anisotropy of epitaxial MgO/Fe/MgO films studied by network analyzer ferromagnetic resonance

Counil, G.; Joo-Von Kim; Devolder, T.; Crozat, P.; Chappert, C.; Cebollada, Alfonso
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 258934 bytes; application/pdf
ENG
Relevância na Pesquisa
56.25%
The dynamic magnetic properties of MgO/Fe epitaxial thin films are investigated through a network analyzer ferromagnetic resonance in the 0–26-GHz range. The high-frequency response is measured for applied in-plane magnetic fields comparable to the fourfold magnetocrystalline anisotropy of the film, resulting in large-angle in-plane quasistatic motion of the magnetization. We show that the variation of the resonance frequency with both the amplitude and the direction of the external field is in good agreement with the ferromagnetic resonance equations, allowing precise determination of the anisotropy.; This work was supported by the European Communities Human Potential program under Contract No. HRPN-CT-2002-00318 ULTRASWITCH and by the Spanish Commission of Science and Technology. The authors would like to thank J. L. Costa-Krämer for his help with Kerr measurements and J. L. Menendez for helpful discussions.; Peer reviewed

Effect of a capping layer on the magnetic properties of island nanostructured Fe(110)

Calleja, J. F.; Contreras, M. C.; Matarranz, R.; Navarro, E.; Huttel, Yves; Cebollada, Alfonso; Armelles Reig, Gaspar
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 79014 bytes; application/pdf
ENG
Relevância na Pesquisa
56.33%
We present a study on the magnetic anisotropy and magnetization reversal of Fe(110) islands grown on Al2O3 versus the island size, the island size distribution, and the magnetic interaction between islands. For small islands magnetically connected via a polarizable capping layer, the samples behave as a uniform film with an induced uniaxial in-plane anisotropy. Magnetically isotropic samples are obtained when the islands size is increased. Transverse susceptibility measurements show that the magnetic anisotropy of the particles is macroscopically averaged due to the interisland magnetic interaction. The island size distribution is correlated to the magnetic anisotropy field dispersion. When the capping layer material is Al, a superparamagnetic behavior is found due to the absence of the interisland interaction.; The Spanish Commission of Science and Technology is acknowledged for financial support. One of the authors sY.H.d thanks the “Ramón y Cajal” program.; Peer reviewed

Magnetic polarization of copper in Cu-capped Co clusters

García, L. M.; Bartolomé, Fernando; Bartolomé, Juan; Luis, Fernando
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 10752 bytes; application/octet-stream
ENG
Relevância na Pesquisa
56.21%
4 pages, 4 figures.- et al.; Magnetic anisotropy of Co nanoparticles homogeneously dispersed in alumina is increased by capping the particles with copper. In the present work, we investigate this effect by measuring X-ray magnetic circular dichroism (XMCD) at the K and L2,3 edges of Co and Cu atoms. We demonstrate that orbital-to-spin ratio at the Co 3d states is increased by capping with Cu, explaining the observed enhancement of the macroscopic anisotropy. Hybridization between Co and Cu at the interface produces an electronic transfer between them. Clear induced magnetic moments are observed in copper, both in the 4p states and in the 3d states.; Peer reviewed

Pinned synthetic ferrimagnets with perpendicular anisotropy and tuneable exchange bias

Sort Viñas, Jordi; Rodmacq, B.; Auffret, S.; Dieny, B.
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2003 ENG
Relevância na Pesquisa
56.25%
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.; Pinned synthetic ferrimagnets (syFerri) with perpendicular-to-plane magnetic anisotropy, of the form AP1/Ru/AP2/FeMn [where AP1 and AP2 are (Co/Pt) multilayers], have been prepared and characterized. The magnitudes of the exchange bias fields of both AP1 and AP2 can be tuned at room temperature by simply varying the relative number of (Co/Pt) repeats in each multilayer. This effect can be quantitatively interpreted by considering the different energy contributions involved during magnetization reversal. Moreover, from the values of these fields, the characteristic parameters of the system (i.e., coupling strength through the Ru and AP2/FeMn pinning energy), can be evaluated. Interestingly, an extended plateau with a virtually constant magnetization is observed around zero field when the number of Co/Pt repeats in AP1 is equal or larger than in AP2. This is very appealing for field sensor or memories applications using spin valves or tunnel junctions with perpendicular anisotropy, since it offers a large dynamic range over which the magnetic configuration of the syFerri remains stable.

Magnetocaloric effect in random magnetic anisotropy materials

Bohigas i Janoher, Xavier; Tejada, J.; Torres Canals, Francesc; Arnaudas, José Ignacio; Joven, Enrique; Del Moral, Agustín
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2002 ENG
Relevância na Pesquisa
56.17%
In this letter we report the results of entropy variations in random anisotropy magnets composed of TbxY1−xAl2, with x=0.15, 0.20, 0.25, 0.35, 0.40, and 0.50. We discovered large entropy variation associated with the spin glass to paramagnetictransition. Both temperature transition and entropy changes were studied at different temperatures and with different compositions. Our conclusion is that these materials are suitable candidates for use as magnetic refrigerants in a temperature range below 40 K.