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Search Results: 1 - 10 of 219351 matches for " C. Deranlot "
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Enhancement of the Spin Accumulation at the Interface Between a Spin-Polarized Tunnel Junction and a Semiconductor
M. Tran,H. Jaffres,C. Deranlot,J. -M. George,A. Fert,A. Miard,A. Lemaitre
Physics , 2008, DOI: 10.1103/PhysRevLett.102.036601
Abstract: We report on spin injection experiments at a Co/Al$_2$O$_3$/GaAs interface with electrical detection. The application of a transverse magnetic field induces a large voltage drop $\Delta V$ at the interface as high as 1.2mV for a current density of 0.34 nA.$\mu m^{-2}$. This represents a dramatic increase of the spin accumulation signal, well above the theoretical predictions for spin injection through a ferromagnet/semiconductor interface. Such an enhancement is consistent with a sequential tunneling process via localized states located in the vicinity of the Al$_2$O$_3$/GaAs interface. For spin-polarized carriers these states act as an accumulation layer where the spin lifetime is large. A model taking into account the spin lifetime and the escape tunneling time for carriers travelling back into the ferromagnetic contact reproduces accurately the experimental results.
Coupling efficiency for phase locking of a spin transfer oscillator to a microwave current
B. Georges,J. Grollier,M. Darques,V. Cros,C. Deranlot,B. Marcilhac,A. Fert,G. Faini
Physics , 2008, DOI: 10.1103/PhysRevLett.101.017201
Abstract: The phase locking behavior of spin transfer nano-oscillators (STNOs) to an external microwave signal is experimentally studied as a function of the STNO intrinsic parameters. We extract the coupling strength from our data using the derived phase dynamics of a forced STNO. The predicted trends on the coupling strength for phase locking as a function of intrinsic features of the oscillators i.e. power, linewidth, agility in current, are central to optimize the emitted power in arrays of mutually coupled STNOs.
Anisotropic magneto-Coulomb effect versus spin accumulation in a ferromagnetic single-electron device
A. Bernand-Mantel,P. Seneor,K. Bouzehouane,S. Fusil,C. Deranlot,F. Petroff,A. Fert
Physics , 2011, DOI: 10.1103/PhysRevB.84.180413
Abstract: We investigate the magneto-transport characteristics of nanospintronics single-electron devices. The devices consist of single non-magnetic nano-objects (nanometer size nanoparticles of Al or Cu) connected to Co ferromagnetic leads. The comparison with simulations allows us attribute the observed magnetoresistance to either spin accumulation or anisotropic magneto-Coulomb effect (AMC), two effects with very different origins. The fact that the two effects are observed in similar samples demonstrates that a careful analysis of Coulomb blockade and magnetoresistance behaviors is necessary in order to discriminate them in magnetic single-electron devices. As a tool for further studies, we propose a simple way to determine if spin transport or AMC effect dominates from the Coulomb blockade I-V curves of the spintronics device.
Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles
R. López-Ruiz,F. Luis,J. Sesé,J. Bartolomé,C. Deranlot,F. Petroff
Physics , 2011, DOI: 10.1209/0295-5075/89/67011
Abstract: We study, by means of magnetic susceptibility and magnetic aging experiments, the nature of the glassy magnetic dynamics in arrays of Co nanoparticles, self-organized in N layers from N=1 (two-dimensional limit) up to N=20 (three-dimensional limit). We find no qualitative differences between the magnetic responses measured in these two limits, in spite of the fact that no spin-glass phase is expected above T=0 in two dimensions. More specifically, all the phenomena (critical slowing down, flattening of the field-cooled magnetization below the blocking temperature and the magnetic memory induced by aging) that are usually associated with this phase look qualitatively the same for two-dimensional and three-dimensional arrays. The activated scaling law that is typical of systems undergoing a phase transition at zero temperature accounts well for the critical slowing down of the dc and ac susceptibilities of all samples. Our data show also that dynamical magnetic correlations achieved by aging a nanoparticle array below its superparamagnetic blocking temperature extend mainly to nearest neighbors. Our experiments suggest that the glassy magnetic dynamics of these nanoparticle arrays is associated with a zero-temperature spin-glass transition.
Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers
A. V. Ramos,M. -J. Guittet,J. -B. Moussy,R. Mattana,C. Deranlot,F. Petroff,C. Gatel
Physics , 2007, DOI: 10.1063/1.2787880
Abstract: We report direct experimental evidence of room temperature spin filtering in magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via tunneling magnetoresistance (TMR) measurements. Pt(111)/CoFe2O4(111)/gamma-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown in order to obtain a high quality system, capable of functioning at room temperature. Spin polarized transport measurements reveal significant TMR values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a unique bias voltage dependence that has been theoretically predicted to be the signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4 tunnel barriers therefore provide a model system to investigate spin filtering in a wide range of temperatures.
Hysteretic magnetic pinning and reversible resistance switching in High-Tc superconductor/ferromagnet multilayers
C. Visani,P. J. Metaxas,A. Collaudin,B. Calvet,R. Bernard,J. Briatico,C. Deranlot,K. Bouzehouane,J. E. Villegas
Physics , 2011, DOI: 10.1103/PhysRevB.84.054539
Abstract: We study a high-TC superconducting (YBa2Cu3O7-d) / ferromagnetic (Co/Pt multilayer) hybrid which exhibits resistance switching driven by the magnetic history: depending on the direction of the external field, a pronounced decrease or increase of the mixed-state resistance is observed as magnetization reversal occurs within the Co/Pt multilayer. We demonstrate that stray magnetic fields cause these effects via i) creation of vortices/antivortices and ii) magnetostatic pinning of vortices that are induced by the external field.
Microwave excitations associated with a wavy angular dependence of the spin transfer torque : model and experiments
O. Boulle,V. Cros,J. Grollier,L. G. Pereira,C. Deranlot,F. Petroff,G. Faini,J. Barnas,A. Fert
Physics , 2007, DOI: 10.1103/PhysRevB.77.174403
Abstract: The spin transfer torque (STT) can lead to steady precession of magnetization without any external applied field in magnetic spin valve where the magnetic layer have very different spin diffusion length. This effect is associated with an unusual angular dependence of the STT, called "wavy" (WAD-STT), predicted in the frame of diffusive models of spin transfer. In this article, we present a complete experimental characterization of the magnetization dynamics in the presence of a WAD-STT. The results are compared to the prediction of the magnetization dynamics obtained by single domain magnetic simulations (macrospin approximation). The macrospin simulations well reproduced the main static and dynamical experimental features (phase diagram, R(I) curves, dependence of frequency with current and field) and suggest that the dynamical excitations observed experimentally are associated with a large angle out-of-plane precession mode. The present work validates the diffusive models of the spin transfer and underlines the role of the spin accumulation and the spin relaxation effects on the STT.
Extrinsic Spin Hall Effect Induced by Iridium Impurities in Copper
Y. Niimi,M. Morota,D. H. Wei,C. Deranlot,M. Basletic,A. Hamzic,A. Fert,Y. Otani
Physics , 2011, DOI: 10.1103/PhysRevLett.106.126601
Abstract: We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, $(2.1 \pm 0.6)$% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy.
Shaped angular dependence of the spin transfer torque and microwave generation without magnetic field
O. Boulle,V. Cros,J. Grollier,L. G. Pereira,C. Deranlot,F. Petroff,G. Faini,J. Barnas,A. Fert
Physics , 2007, DOI: 10.1038/nphys618
Abstract: The generation of oscillations in the microwave frequency range is one of the most important applications expected from spintronics devices exploiting the spin transfer phenomenon. We report transport and microwave power measurements on specially designed nanopillars for which a non-standard angular dependence of the spin transfer torque (wavy variation) is predicted by theoretical models. We observe a new kind of current-induced dynamics that is characterized by large angle precessions in the absence of any applied field, as this is also predicted by simulation with such a wavy angular dependence of the torque. This type of non-standard nanopillars can represent an interesting way for the implementation of spin transfer oscillators since they are able to generate microwave oscillations without applied magnetic field. We also emphasize the theoretical implications of our results on the angular dependence of the torque.
Giant Spin Hall Effect Induced by Skew Scattering from Bismuth Impurities inside Thin Film CuBi Alloys
Y. Niimi,Y. Kawanishi,D. H. Wei,C. Deranlot,H. X. Yang,M. Chshiev,T. Valet,A. Fert,Y. Otani
Physics , 2012, DOI: 10.1103/PhysRevLett.109.156602
Abstract: We demonstrate that a giant spin Hall effect (SHE) can be induced by introducing a small amount of Bi impurities in Cu. Our analysis based on a new 3-dimensional finite element treatment of spin transport shows that the sign of the SHE induced by the Bi impurities is negative and its spin Hall (SH) angle amounts to -0.24. Such a negative large SH angle in CuBi alloys can be explained by applying the resonant scattering model proposed by Fert and Levy [Phys. Rev. Lett. 106, 157208 (2011)] to 6p impurities.
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