C. Gatel

Publications (6)7.57 Total impact

• Article: Crystalline structure of oxide-based epitaxial tunnel junctions

  C. Mocuta, A. Barbier, A. V. Ramos, M.-J. Guittet, J.-B. Moussy, S. Stanescu, C. Gatel, R. Mattana, C. Deranlot, F. Petroff
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  ABSTRACT: Epitaxial metal/oxide based magnetic tunnel-junctions (MTJ) are valuable model systems to investigate the influence of the crystallinity of individual layers on the magnetic properties. We have non-destructively studied the effect of the optical lithography procedure on the crystalline structure of MTJ’s with lateral spatial resolution by performing local x-ray diffraction experiments using a microfocused x-ray spot. We demonstrate that the lithography process produces distortion effects on the crystalline structure of the layers near the edges of the lithographed junction. These distortions are present on all the constituent layers and are most probably driven by the elastic constants of the materials. They translate into tilts of the crystalline planes in the vicinity of the edges and propagate towards the center of the junction; the tilt’s amplitude (up to several degrees) and sign (concave or convex) depend on the junction’s shape, size and the type of materials (interfaces) used. We report results for junctions made with two types of metal-oxide interfaces (Co/CoFe2O4 and Co/Fe3O4), with sizes from 10 to 150 μm and various shapes (square-, rectangle- and disk-like).
  The European Physical Journal Special Topics 05/2012; 167(1):53-58. · 1.56 Impact Factor
• Source

  Available from: ArXiv

  Article: 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
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  ABSTRACT: The authors report direct experimental evidence of room temperature spin filtering in magnetic tunnel junctions (MTJs) containing Co Fe ₂ O ₄ tunnel barriers via tunneling magnetoresistance (TMR) measurements. Pt (111)/ Co Fe ₂ O ₄(111)/γ- Al ₂ O ₃(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. Co Fe ₂ O ₄ tunnel barriers therefore provide a model system to investigate spin filtering in a wide range of temperatures.
  Applied Physics Letters 10/2007; · 3.84 Impact Factor
• Article: Magnetotransport properties of Fe3O4 epitaxial thin films: Thickness effects driven by antiphase boundaries

  A. V. Ramos, J.-B. Moussy, M.-J. Guittet, A. M. Bataille, M. Gautier-Soyer, M. Viret, C. Gatel, P. Bayle-Guillemaud, E. Snoeck
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  ABSTRACT: We present an in-depth study of the magnetotransport properties of epitaxial Fe3O4 films as a function of film thickness. The films, grown on α-Al2O3(0001) single crystals by atomic-oxygen assisted molecular beam epitaxy, exhibit high structural order and abrupt interfaces. These films contain antiphase boundaries (APBs), the density of which is strongly dependent on film thickness. A series of resistivity and magnetoresistance measurements demonstrate a systematic evolution of these properties with decreasing film thickness, revealing the impact of APBs on the transport properties in the films. We present a model based on the spin-polarized transport across an antiferromagnetically coupled APB in order to successfully reproduce our experimental data over a large range of applied magnetic fields. The comparison of this model with experimental results further clarifies the mechanism of the anomalous magnetotransport behavior in Fe3O4.
  Journal of Applied Physics 11/2006; 100(10):103902-103902-8. · 2.17 Impact Factor
• Article: Thickness dependence of anomalous magnetic behavior in epitaxial Fe_ {3} O_ {4}(111) thin films: Effect of density of antiphase boundaries

  J.-B. Moussy, S. Gota, A. Bataille, M.-J. Guittet, M. Gautier-Soyer, F. Delille, B. Dieny, F. Ott, T. D. Doan, P. Warin, P. Bayle-Guillemaud, C. Gatel, E. Snoeck
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  ABSTRACT: We study the magnetic behavior of Fe3O4(111) thin films with thicknesses between 5 nm and 50 nm. The films are epitaxially grown on α-Al2O3(0001) single crystals by atomic-oxygen-assisted molecular beam epitaxy. The Fe3O4(111) thin films exhibit high structural order with sharp interfaces and low roughness and exhibit a Verwey transition for thicknesses above 8 nm. However, the samples have magnetic properties that deviate from the bulk ones. The magnetic moment varies between 2.4μB for 5-nm-thick film and 3.2μB for 50-nm-thick film in a field of 1.2 T, which is lower than that of bulk samples (4.1μB∕Fe3O4 formula). Still the magnetic saturation is never reached, even in fields as large as 2 T. The thinner the film, the slower the approach to saturation. Structural analysis, performed using high-resolution transmission electron microscopy, reveals the presence of antiphase boundaries (APB’s), the density of which decreases when the thickness increases. Using a model of ferromagnetic domains separated by antiferromagnetically sharp interfaces, we show that the slow approach to saturation observed in the films as a function of thickness is driven by the APB density.
  Phys. Rev. B. 70(17).
• Article: Influence of a metallic or oxide top layer in epitaxial magnetic bilayers containing CoFe_ {2} O_ {4}(111) tunnel barriers

  A. V. Ramos, J.-B. Moussy, M.-J. Guittet, M. Gautier-Soyer, C. Gatel, P. Bayle-Guillemaud, B. Warot-Fonrose, E. Snoeck
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  ABSTRACT: We investigate the interaction of CoFe2O4(111) tunnel barriers with Co and Fe3O4 electrodes in light of their potential as room temperature spin filters. The question of the exchange coupling that often prohibits the independent switching between a magnetic tunnel barrier and its magnetic electrode is addressed, as is the difference between an oxide/metal and oxide/oxide system. Our study of the magnetic reversal in the CoFe2O4∕Co and CoFe2O4∕Fe3O4 bilayers, supported by a detailed structural and chemical analysis of the samples and their interfaces, clearly evidences the effect of a metallic or an oxide interface. An unusual exchange spring magnet behavior arises in the case of the CoFe2O4∕Fe3O4 samples due to the superexchange interactions found in these ferrimagnetic oxides. This unique exchange phenomenon at the oxide-oxide interface ultimately leads to a bilayer system displaying a two-phase magnetization loop without the insertion of a nonmagnetic spacer.
  Phys. Rev. B. 75(22).
• Article: Epitaxial growth and ferrimagnetic behavior of MnFe(2)O(4)(111) ultrathin layers for room-temperature spin filtering

  S Matzen, J -B Moussy, R Mattana, K Bouzehouane, C Deranlot, F Petroff, J C Cezar, M -A Arrio, Ph. Sainctavit, C Gatel, B Warot-Fonrose, Y Zheng
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  ABSTRACT: We report on the epitaxial growth and physical properties of spinel MnFe(2)O(4)(111) thin films with thicknesses down to 2 nm. The thin films, grown on alpha-Al(2)O(3)(0001) single crystals or Pt(111) buffer layers by oxygen-assisted molecular beam epitaxy, exhibit high structural order with sharp interfaces and low roughness. The electrical and magnetic properties are carefully investigated and it is shown that MnFe(2)O(4)(111) ultrathin films keep an insulating and ferrimagnetic behavior at room temperature. Special attention is given to the iron/manganese valence state and the cationic ordering. X-ray absorption spectroscopy and magnetic circular dichroism measurements reveal that thin films contain mainly Fe(3+) and Mn(2+) cations, distributed predominantly in a normal spinel structure. This study proves the high potential of MnFe(2)O(4) to be used as a magnetic tunnel barrier for spin filtering applications at room temperature.
  PHYSICAL REVIEW B. 83(18).