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Search Results: 1 - 10 of 671577 matches for " J. -C. Rojas-Sánchez "
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Spin Pumping and Inverse Spin Hall Effect in Platinum: The Essential Role of Spin-Memory Loss at Metallic Interfaces
J. -C. Rojas-Sánchez,N. Reyren,P. Laczkowski,W. Savero,J. -P. Attané,C. Deranlot,M. Jamet,J. -M. George,L. Vila,H. Jaffrès
Physics , 2013, DOI: 10.1103/PhysRevLett.112.106602
Abstract: Through combined ferromagnetic resonance, spin-pumping and inverse spin Hall effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate consistent values of spin diffusion length $\ell_{\rm sf}^{\rm Pt}=3.4\pm0.4$ nm and of spin Hall angle $\theta_{\rm SHE}^{\rm Pt}=0.051\pm0.004$ for Pt. Our data and model emphasize on the partial depolarization of the spin current at each interface due to spin-memory loss. Our model reconciles the previously published spin Hall angle values and explains the different scaling lengths for the ferromagnetic damping and the spin Hall effect induced voltage.
Perpendicular magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers via the Spin Hall Effect of Pt
J. -C. Rojas-Sánchez,P. Laczkowski,J. Sampaio,S. Collin,K. Bouzehouane,N. Reyren,H. Jaffrès,A. Mougin,J. -M. George
Physics , 2015,
Abstract: We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 0.3 TA/m$^2$. In these experiments we demonstrate a full control of each stage: i)the {\O}rsted field controls the domain nucleation and ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and N\'eel like due to the interfacial Dzyaloshinskii-Moriya interaction.
Spin Pumping and Inverse Spin Hall Effect in Germanium
J. -C. Rojas-Sánchez,M. Cubukcu,A. Jain,C. Vergnaud,C. Portemont,C. Ducruet,A. Barski,A. Marty,L. Vila,J. -P. Attané,E. Augendre,G. Desfonds,S. Gambarelli,H. Jaffrès,J. -M. George,M. Jamet
Physics , 2013, DOI: 10.1103/PhysRevB.88.064403
Abstract: We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped $n$-Ge and we could estimate the spin Hall angle at room temperature to be $\approx$0.001.
Experimental evidences of a large extrinsic spin Hall effect in AuW alloy
P. Laczkowski,J. -C. Rojas-Sánchez,W. Savero-Torres,H. Jaffrès,N. Reyren,C. Deranlot,L. Notin,C. Beigné,A. Marty,J. -P. Attané,L. Vila,J. -M. George,A. Fert
Physics , 2014, DOI: 10.1063/1.4870835
Abstract: We report an experimental study of a gold-tungsten alloy (7% at. W concentration in Au host) displaying remarkable properties for spintronics applications using both magneto-transport in lateral spin valve devices and spin-pumping with inverse spin Hall effect experiments. A very large spin Hall angle of about 10% is consistently found using both techniques with the reliable spin diffusion length of 2 nm estimated by the spin sink experiments in the lateral spin valves. With its chemical stability, high resistivity and small induced damping, this AuW alloy may find applications in the nearest future.
Evaluation of the spin diffusion length of AuW alloy by spin absorption experiments in the limit of large spin-orbit interactions
P. Laczkowski,H. Jaffrès,W. Savero-Torres,J. -C. Rojas-Sánchez,Y. Fu,N. Reyren,C. Deranlot,L. Notin,C. Beigné,J. -P. Attané,L. Vila,J. -M. George,A. Marty
Physics , 2015,
Abstract: The knowledge of the spin diffusion length $\lambda_{A}$ is a prerequisite for the estimation of the spin Hall angle. We investigate spin current absorption of materials with small $\lambda_{A}$ using AuW stripes inserted in lateral spin-valves. Width variations of the AuW stripe lead to drastic changes of the spin absorption, which cannot be explained by conventional analysis. We show that the spin-current polarization and the spin accumulation attenuation in the vicinity of the spin absorber must to be precisely taken into account for accurate estimation of $\lambda_{A}$. We propose an analytical model supported by numerical calculations that allows to extract proper $\lambda_{A}$ values of spin Hall effect materials.
Spin-pumping into surface states of topological insulator α-Sn, spin to charge conversion at room temperature
J. -C. Rojas-Sánchez,S. Oyarzun,Y. Fu,A. Marty,C. Vergnaud,S. Gambarelli,L. Vila,M. Jamet,Y. Ohtsubo,A. Taleb-Ibrahimi,P. Le Fèvre,F. Bertran,N. Reyren,J. -M. George,A. Fert
Physics , 2015,
Abstract: We present experimental results on the conversion of a spin current into a charge current by spin pumping into the Dirac cone with helical spin polarization of the elemental topological insulator (TI) {\alpha}-Sn[1-3]. By angle-resolved photoelectron spectroscopy (ARPES) we first confirm that the Dirac cone at the surface of {\alpha}-Sn (0 0 1) layers subsists after covering with Ag. Then we show that resonant spin pumping at room temperature from Fe through Ag into {\alpha}-Sn layers induces a lateral charge current that can be ascribed to the Inverse Edelstein Effect[4-5]. Our observation of an Inverse Edelstein Effect length[5-6] much longer than for Rashba interfaces[5-10] demonstrates the potential of the TI for conversion between spin and charge in spintronic devices. By comparing our results with data on the relaxation time of TI free surface states from time-resolved ARPES, we can anticipate the ultimate potential of TI for spin to charge conversion and the conditions to reach it.
Algunas consideraciones sobre caries dental, fluoruros, su metabolismo y mecanismos de acción
Rojas-Sánchez,Fátima;
Acta Odontológica Venezolana , 2008,
Abstract: this article presents a review of the current vision about dental caries, and microorganisms associated to the development of dental caries. mechanisms of dental caries lesion, the role of fluoride through its mechanisms of action: demineralization, remineralization and antibacterial action. a scheme of the metabolism of fluorides, absorption, distribution and excretion is presented. some considerations about the initiation of the natural water fluoridation program in the world, and about the threshold dose of fluoride, and dental fluorosis.
Algunas consideraciones sobre caries dental, fluoruros, su metabolismo y mecanismos de acción
Fátima Rojas-Sánchez
Acta Odontológica Venezolana , 2008,
Abstract: El presente artículo esta dirigido a estudiantes y profesionales de la odontología interesados en profundizar sus conocimientos sobre caries dental y fluoruros. El objetivo primordial de la presente revisión es actualizar algunos conceptos sobre caries dental, su inicio y desarrollo, así como el papel principal que tienen los fluoruros como agente anticariogénico de primera elección para controlar o revertir la historia natural de la lesión cariosa. Se describe brevemente que son los fluoruros, origen, abundancia en la naturaleza y comportamiento químico, así como, los mecanismos de acción: inhibición de la desmineralización, remineralización y acción antibacteriana. De igual manera se mencionan aspectos relevantes sobre su metabolismo, absorción, distribución y excreción, así como su farmacocinética. This article presents a review of the current vision about dental caries, and microorganisms associated to the development of dental caries. Mechanisms of dental caries lesion, the role of fluoride through its mechanisms of action: demineralization, remineralization and antibacterial action. A scheme of the metabolism of fluorides, absorption, distribution and excretion is presented. Some considerations about the initiation of the natural water fluoridation program in the world, and about the threshold dose of fluoride, and dental fluorosis.
Efecto inhibitorio del nonanoato de potasio y el fluoruro de sodio en la acidogenicidad de la placa dental humana in vitro: Nonanoato de Potasio y Fluoruros como inhibidores de la placa dental
Rojas-Sánchez,Fátima; Lalaguna,Fernando; Infante,Yanira; Acevedo,Ana Maria;
Acta Odontológica Venezolana , 2000,
Abstract: nonanoic acid a saturated 9-carbon fatty acid, was earlier shown to reduce fissure caries in rats when included in their diet (hayes and berkovitz, 1979). griffiths in 1979 showed that potassium nonanoate added to sugar-rinses inhibits plaque bacteria in man. the aim of this study was to evaluate the effect of potassium nonanoate (nk), sodium fluoride (naf) and their combination on acid production, and this was assessed by back tritation using the method described by hayes and roberts, (1980). at ph 7.4 kn and naf added separately reduced acid production by 45.0% and 54.5%, respectively, compared to the control. the reduction in acid production when using the compounds in combination was 39%. at ph 5.5, both kn and naf alone showed 21.2% and 29.3% inhibition, respectively, and when combined this inhibition increased to 49.3%. at ph 5.5 a cumulative effect of kn and naf was observed. we conclude that at acid ph both compounds, kn+naf combined would be the best to be effective.
Efecto inhibitorio del nonanoato de potasio y el fluoruro de sodio en la acidogenicidad de la placa dental humana in vitro: Nonanoato de Potasio y Fluoruros como inhibidores de la placa dental
Fátima Rojas-Sánchez,Fernando Lalaguna,Yanira Infante,Ana Maria Acevedo
Acta Odontológica Venezolana , 2000,
Abstract: El ácido nonanoico es un ácido graso saturado de 9 carbonos el cual se ha demostrado reduce la aparición de caries de fisura en ratas cuando es incluido en la dieta (Hayes y Berkovitz, 1979). En 1979, Griffiths demostró que el nonanoato de potasio agregado en enjuagues con sacarosa inhibe la producción de ácidos por parte de las bacterias de la placa dental en humanos. El objetivo de esta investigación fue estudiar el efecto de ácidos grasos y fluoruros en la producción de cidos en placa dental de humanos in vitro. Para ello se recolectó placa dental en ayunas de 3 horas, en ni os con caries activa y con edades comprendidas entre los 5 y 12 a os. La producción de ácidos fue determinada por el método de titulación reportado por Hayes y Roberts (1980) luego de la adición de glucosa exógena. Los resultados demostraron que a pH 7,4 el NK (3mM) y el NaF (13 mM) produjeron una inhibición en la producción de ácidos en un 45,0% y 54,5% respectivamente, mientras que con la mezcla se observó una reducción de un 39%. A pH 5,5 el NK y el NaF a una concentración de 0,26 mM produjeron una inhibición de 21.2% y 29,3% respectivamente, y cuando se mezclaron esta inhibición se incrementó a 49,3%. Estos resultados sugieren que a pHs cercanos a la neutralidad (7,4) no hay efecto aditivo del NK y NaF, mientras que a pH ácido (5,5) la combinación de estos compuestos incrementó significativamente (p<0.01) su efectividad. Nonanoic acid a saturated 9-carbon fatty acid, was earlier shown to reduce fissure caries in rats when included in their diet (Hayes and Berkovitz, 1979). Griffiths in 1979 showed that potassium nonanoate added to sugar-rinses inhibits plaque bacteria in man. The aim of this study was to evaluate the effect of potassium nonanoate (NK), sodium fluoride (NAF) and their combination on acid production, and this was assessed by back tritation using the method described by Hayes and Roberts, (1980). At pH 7.4 KN and NaF added separately reduced acid production by 45.0% and 54.5%, respectively, compared to the control. The reduction in acid production when using the compounds in combination was 39%. At pH 5.5, both KN and NaF alone showed 21.2% and 29.3% inhibition, respectively, and when combined this inhibition increased to 49.3%. At pH 5.5 a cumulative effect of KN and NaF was observed. We conclude that at acid pH both compounds, KN+NaF combined would be the best to be effective.
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