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114 results on '"Vaurès A"'

3. Spin injection in a single metallic nanoparticle: a step towards nanospintronics

Author

Bernand-Mantel, A., Seneor, P., Lidgi, N., Munoz, M., Cros, V., Fusil, S., Bouzehouane, K., Deranlot, C., Vaures, A., Petroff, F., and Fert, A.

Subjects
Condensed Matter - Materials Science
Abstract

We have fabricated nanometer sized magnetic tunnel junctions using a new nanoindentation technique in order to study the transport properties of a single metallic nanoparticle. Coulomb blockade effects show clear evidence for single electron tunneling through a single 2.5 nm Au cluster. The observed magnetoresistance is the signature of spin conservation during the transport process through a non magnetic cluster., Comment: 3 pages

Published
2006
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4. Magnetization reversal by injection and transfer of spin: experiments and theory

Author

Fert, A., Cros, V., George, J. -M., Grollier, J., Jaffres, H., Hamzic, A., Vaures, A., Faini, G., Youssef, J. Ben, and Gall, H. Le

Subjects
Condensed Matter - Materials Science
Abstract

Reversing the magnetization of a ferromagnet by spin transfer from a current, rather than by applying a magnetic field, is the central idea of an extensive current research. After a review of our experiments of current-induced magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we have worked out for the calculation of the current-induced torque and the interpretation of the experiments.

Published
2003
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5. Switching a spin-valve back and forth by current-induced domain wall motion

Author

Grollier, J., Boulenc, P., Cros, V., Hamzic, A., Vaures, A., Fert, A., and Faini, G.

Subjects
Condensed Matter - Materials Science
Abstract

We have studied the current-induced displacement of a domain wall (DW) in the permalloy (Py) layer of a Co/Cu/Py spin valve structure at zero and very small applied field. The displacement is in opposite direction for opposite dc currents, and the current density required to move DW is only of the order of 10^6 A/cm^2. For H = 3 Oe, a back and forth DW motion between two stable positions is observed. We also discuss the effect of an applied field on the DW motion., Comment: 4 pages, 3 figures

Published
2003
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6. Switching the magnetic configuration of a spin valve by current induced domain wall motion

Author

Grollier, J., Lacour, D., Cros, V., Hamzic, A., Vaures, A., Fert, A., Adam, D., and Faini, G.

Subjects
Condensed Matter - Materials Science
Abstract

We present experimental results on the displacement of a domain wall by injection of a dc current through the wall. The samples are 1 micron wide long stripes of a CoO/Co/Cu/NiFe classical spin valve structure. The stripes have been patterned by electron beam lithography. A neck has been defined at 1/3 of the total length of the stripe and is a pinning center for the domain walls, as shown by the steps of the giant magnetoresistance curves at intermediate levels (1/3 or 2/3) between the resistances corresponding to the parallel and antiparallel configurations. We show by electric transport measurements that, once a wall is trapped, it can be moved by injecting a dc current higher than a threshold current of the order of magnitude of 10^7 A/cm^2. We discuss the different possible origins of this effect, i.e. local magnetic field created by the current and/or spin transfer from spin polarized current., Comment: 3 pages, 3 figures

Published
2002
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7. Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions

Author

Luis, F., Torres, J. M., Garcia, L. M., Bartolome, J., Stankiewicz, J., Petroff, F., Fettar, F., Maurice, J. -L, and Vaures, A.

Subjects
Condensed Matter - Materials Science
Abstract

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared to previous structural characterizations. The distribution of activation energies was independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal is shown to proceed classically down to the lowest temperature investigated (1.8 K)., Comment: 13 figures submitted to Phys. Rev. B

Published
2001
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17. A magnetometry study of Co oxidation in Co/MgO bilayers grown by sputtering.

Author

Lu, Y., Deranlot, C., Vaurès, A., Petroff, F., and George, J-M.

Subjects
OXIDATION, SPUTTERING (Physics), MAGNETIC properties, MAGNETORESISTANCE, QUANTUM tunneling, MAGNESIUM, OXIDES
Abstract

One of the critical challenges during fabrication of magnetic tunnel junctions is to avoid the magnetic bottom electrode oxidation, considered as a spin depolarization source that lowers the tunneling magnetoresistance effect. In this paper, we present a study of the magnetic properties of Co/MgO bilayers as a function of several sputtering growth parameters by using a superconducting quantum interference device magnetometer. We demonstrate the high sensitivity of the magnetic properties to the oxidation of the Co layer and identify the relevant parameters to optimize the MgO growth process. [ABSTRACT FROM AUTHOR]

Published
2008
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19. Inverse Tunnel Magnetoresistance inCo/SrTiO3/La0.7Sr0.3MnO3: New Ideas on Spin-Polarized Tunneling

Author

François Montaigne, Agnès Barthélémy, R. Lyonnet, Albert Fert, A. Vaurès, Pierre Seneor, J.-P. Contour, and J. M. De Teresa

Subjects
Physics, Condensed matter physics, Spin polarization, Spin polarized tunneling, General Physics and Astronomy, Inverse, Electron, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Condensed Matter::Materials Science, Tunnel magnetoresistance, Density of states, Condensed Matter::Strongly Correlated Electrons, Quantum tunnelling, Spin-½
Abstract

We report tunnel magnetoresistance (TMR) measurements on $\mathrm{Co}/{\mathrm{SrTiO}}_{3}/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ junctions. The half-metallic ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ electrode is used as a spin analyzer. The large $(\ensuremath{-}50%)$ inverse TMR indicates a negative spin polarization of Co, in agreement with the density of states (DOS) of the $d$ band in Co. The bias dependence of the TMR, with a maximum inverse TMR at $\ensuremath{-}0.4\mathrm{V}$ and a crossover to normal TMR above $+0.8\mathrm{V}$, reflects the structure of this DOS. Our results demonstrate that the choice of the insulating barrier can strongly influence and even reverse the spin polarization of tunneling electrons.

Published
1999
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20. Spin-transfer-induced domain wall motion in a spin valve.

Author

Grollier, J., Boulenc, P., Cros, V., Hamzic, A., Vaurès, A., Fert, A., and Faini, G.

Subjects
MAGNETIC fields, SPIN valves, MOTION, POLARIZATION (Nuclear physics), NANOWIRES, PHYSICS
Abstract

We have studied the current-induced displacement of a domain wall (DW) in the permalloy (Py) layer of a Co/Cu/Py spin-valve structure. At zero and very small applied fields (<10 Oe), the displacement is in opposite direction for opposite dc currents, and the current density required to move DW is of the order of a few 106 A/cm2. At higher applied magnetic fields, the DW motion, even though triggered by the current, has its direction controlled by the field. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
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21. Competitive effects of dipolar interactions and a bias magnetic field on the magnetic relaxation times of Co clusters.

Author

Luis, F., Bartolomé, J., Petroff, F., Garcıa, L. M., Vaurès, A., and Carrey, J.

Subjects
MAGNETIC fields, PARAMAGNETISM, MAGNETICS, MAGNETIC dipoles
Abstract

We have investigated, by means of ac susceptibility experiments, the magnetic relaxation of layers of Co nanoclusters (D ≃ 2.6 nm) embedded in Al[SUB2]O[SUB3]. Superparamagnetic blocking takes place at higher temperatures as the number of layers increases. These results are interpreted using a simple model in which dipole--dipole interactions between nearest neighbor particles increase the relaxation time. The influence of interactions is affected by the application of bias magnetic field H. As the magnetic moments of the particles become polarized by H, the blocking temperature approaches the behavior expected for noninteracting particles. [ABSTRACT FROM AUTHOR]

Published
2003
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24. Magnetic relaxation of interacting co clusters: crossover from two- to three-dimensional lattices

Author

Jeremie Torres, Frédéric Petroff, Luis Miguel García, José F. Bartolomé, Fernando Luis, Julian Carrey, and A. Vaurès

Subjects
Magnetization, Materials science, Degree (graph theory), Condensed matter physics, Crossover, General Physics and Astronomy, Magnetic relaxation, Activation energy, k-nearest neighbors algorithm, Layered structure
Abstract

The influence that dipole-dipole interactions exert on the dynamics of the magnetization of nanometer-sized Co clusters has been studied by means of ac and dc susceptibility experiments. These clusters grow in a quasiordered layered structure, where all relevant parameters can be tailored and measured independently. Our data show without ambiguity that the magnetic relaxation becomes slower as the degree of interaction increases. The effective activation energy increases linearly with the number of nearest neighbor clusters, evolving from the value for a 2D layer to the fully 3D behavior, which is nearly reached for five layers. The experimental results agree quantitatively with the predictions of a simple model.

Published
2001

25. Growth of Au clusters on amorphous Al2O3: evidence of cluster mobility above a critical size

Author

J, Carrey, J L, Maurice, F, Petroff, and A, Vaurès

Abstract

We study the 3D growth of clusters during the deposition of Au atoms on amorphous Al2O3. By comparing transmission electron microscopy images of the growth with Monte Carlo simulations, we show that nucleation takes place on substrate defects, but that further stages of growth imply that clusters leave the defects after they have reached a given critical size, and diffuse. An interesting consequence of this property is that, in contrast to intuition, and in a certain range of size, larger clusters are more mobile than smaller ones in this system.

Published
2000

26. Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

Author

Comisión Interministerial de Ciencia y Tecnología, CICYT (España), European Commission, Luis, Fernando, Torres, J. M., García, L. M., Bartolomé, Juan, Stankiewicz, Jolanta, Petroff, F., Fettar, F., Maurice, J.-L., Vaurès, A., Comisión Interministerial de Ciencia y Tecnología, CICYT (España), European Commission, Luis, Fernando, Torres, J. M., García, L. M., Bartolomé, Juan, Stankiewicz, Jolanta, Petroff, F., Fettar, F., Maurice, J.-L., and Vaurès, A.

Abstract

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.2 nm (25–7000 atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared with previous structural characterizations. The distribution of activation energies has been independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal process is shown to proceed classically down to the lowest temperature investigated (1.8 K).

Published
2002

27. Magnetic characterization of granular Co/Al2O3 multilayers

Author

European Commission, Comisión Interministerial de Ciencia y Tecnología, CICYT (España), Torres, J. M., Luis, Fernando, García, L. M., Bartolomé, Juan, Stankiewicz, Jolanta, Petroff, F., Fettar, F., Vaurès, A., European Commission, Comisión Interministerial de Ciencia y Tecnología, CICYT (España), Torres, J. M., Luis, Fernando, García, L. M., Bartolomé, Juan, Stankiewicz, Jolanta, Petroff, F., Fettar, F., and Vaurès, A.

Abstract

We study the magnetic properties of Co clusters with diameters between 0.8 and 3 nm prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data. Comparing this to the distribution of activation energies, obtained from the AC susceptibility, we have determined accurately the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and it increases as the average particle size decreases.

Published
2002

29. Using half-metallic manganite interfaces to reveal insights into spintronics

Author

Bowen, M, primary, Maurice, J-L, additional, Barthélémy, A, additional, Bibes, M, additional, Imhoff, D, additional, Bellini, V, additional, Bertacco, R, additional, Wortmann, D, additional, Seneor, P, additional, Jacquet, E, additional, Vaurès, A, additional, Humbert, J, additional, Contour, J-P, additional, Colliex, C, additional, Blügel, S, additional, and Dederichs, P H, additional

Published
2007
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35. Tunnel magnetoresistance in nanojunctions based on Sr2FeMoO6

Author

Bibes, M., primary, Bouzehouane, K., additional, Barthélémy, A., additional, Besse, M., additional, Fusil, S., additional, Bowen, M., additional, Seneor, P., additional, Carrey, J., additional, Cros, V., additional, Vaurès, A., additional, Contour, J.-P., additional, and Fert, A., additional

Published
2003
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37. Luiset al.Reply

Author

Luis, F., primary, Petroff, F., additional, Torres, J. M., additional, García, L. M., additional, Bartolomé, J., additional, Carrey, J., additional, and Vaurès, A., additional

Published
2003
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