F. Fettar

Publications (7)7.69 Total impact

• Source

  Available from: 144.206.159.178

  Article: Three-dimensional magnetization profile and multiaxes exchange bias in Co antidot arrays

  F. Fettar, L. Cagnon, N. Rougemaille
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  ABSTRACT: Magnetic properties of Cu/Co/Cu trilayers deposited on nanoporous alumina membranes are investigated using a superconducting quantum interference device. Hysteresis loops of the resulting Co antidot arrays show two-step magnetization reversal. Due to oxidation when samples are exposed to air, CoO forms and exchange bias is observed, whether the cooling field is applied within or perpendicular to the surface plane. In the former case, the exchange bias changes sign close to the blocking temperature of Co/CoO. We attribute these effects to the local, crescent shape of the Co films induced by the surface morphology of the membranes, which leads to a three-dimensional magnetization distribution.
  Applied Physics Letters 12/2010; · 3.84 Impact Factor
• Source

  Available from: Nicolas Rougemaille

  Article: 3D magnetization profile and multi-axes exchange bias in Co antidot arrays

  F. Fettar, L. Cagnon, N. Rougemaille
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  ABSTRACT: Cu/Co/Cu trilayers have been deposited on nanoporous alumina membranes. Magnetic properties of the resulting Co antidot arrays are investigated using SQUID magnetometry. Hysteresis loops of these arrays show two-step magnetization reversal. In addition, exchange bias is observed, whether the cooling field is applied within or perpendicular to the surface plane. In the former case, the exchange bias changes sign close to the blocking temperature, and becomes positive. We attribute these effects to the local, crescent shape of the Co films, induced by the surface morphology of the alumina membranes. This morphology leads to a three-dimensional magnetization distribution at the nanoscale. Comment: 3 pages, 3 figures
  08/2010;
• Article: Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

  F. Luis, J. M. Torres, L. M. García, J. Bartolomé, J. Stankiewicz, F. Petroff, F. Fettar, J.-L. Maurice, A. Vaurès
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  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).
  Phys. Rev. B. 02/2002; 65(9).
• Source

  Available from: F. Luis

  Article: Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions

  F. Luis, J. M. Torres, L.M. Garcia, J. Bartolome, J. Stankiewicz, F. Petroff, F. Fettar, J. -L. Maurice, A. Vaures
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  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
  08/2001;
• Source

  Available from: trt.thalesgroup.com

  Article: Evidence for a self-organized growth in granular Co/Al2O3 multilayers

  D. Babonneau, F. Petroff, J.-L. Maurice, F. Fettar, A. Vaurès, A. Naudon
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  ABSTRACT: By sequential deposition of thin layers of cobalt and alumina by sputtering, we have fabricated granular multilayers consisting of successive planes of nanosized cobalt clusters separated by alumina along the growth direction. Combining grazing-incidence small-angle x-ray scattering and transmission electron microscopy experiments, we show that, in a given range of thickness, the vertical arrangement of clusters from plane to plane is not random but shows a topology-induced self-organization. © 2000 American Institute of Physics.
  Applied Physics Letters 05/2000; 76(20):2892-2894. · 3.84 Impact Factor
• Source

  Available from: thalesgroup.com

  Article: Temperature and voltage dependence of the resistance and magnetoresistance in discontinuous double tunnel junctions

  F Fettar, S.-F Lee, F Petroff, A Vaures, P Holody, L F Schelp, A Fert
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  ABSTRACT: We have studied the electric and magnetotransport properties of Co//Al 2 O 3 /Co I /Al 2 O 3 //(Co or Cu) tunnel double junctions, in which the intermediate Co I layer is either granular or percolated clusters and the top electrode is either Co or Cu. In granular junctions, spin-dependent tunneling with Coulomb-blockade effect was observed. The temperature dependence of the resistance can be attributed to two conduction channels in parallel between electrodes via granules and via other channels such as metallic impurities in the insulating layer. Voltage and temperature dependences of the tunnel magnetoresistance are discussed. The Coulomb blockade and the improvement of the antiparallel alignment at low temperature both enhanced the TMR effects.
  652350(75).
• Article: Temperature and voltage dependence of the resistance and magnetoresistance in discontinuous double tunnel junctions

  F. Fettar
  [show abstract] [hide abstract]
  ABSTRACT: We have studied the electric and magnetotransport properties of Co//Al2O3/CoI/Al2O3//(CoorCu) tunnel double junctions, in which the intermediate CoI layer is either granular or percolated clusters and the top electrode is either Co or Cu. In granular junctions, spin-dependent tunneling with Coulomb-blockade effect was observed. The temperature dependence of the resistance can be attributed to two conduction channels in parallel between electrodes via granules and via other channels such as metallic impurities in the insulating layer. Voltage and temperature dependences of the tunnel magnetoresistance are discussed. The Coulomb blockade and the improvement of the antiparallel alignment at low temperature both enhanced the TMR effects.
  Phys. Rev. B. 65(17).