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Articles

1997


  • J. - P. Contour, M. Drouet, O. Durand, J. - L. Maurice, A. Gauzzi, Microstructure and strain relaxation in YBa2Cu3O7/PrBa2Cu3−xGaxO7 superlattices. Physica C: Superconductivity. 282–287, Part 2, 689–690 (1997).
    Résumé : We present X-ray diffraction and transmission electron microscopy observations of microstructure and strain relaxation in YBa2Cu3O7/PrBa2Cu3−xGaxO7 (x= 0.2) superlattices. This work follows a previous study on the influence of strain on the transition width ΔTc in these systems [1].

  • J. - P. Contour, M. Drouet, B. Fisher, L. Patlagan, D. Ravelosona, Structural and electrical properties of PrBa2Cu3-xGaxO7 (x=0.2) thin films and [PrBa2Cu3-xGaxO7)(M)/(YBa2Cu3O7)(N)](P) superlattices grown by pulsed laser deposition. Journal of Alloys and Compounds. 251, 209–212 (1997).
    Résumé : The low temperature resistivity (T \textbackslashtextbackslashtextbackslashtextless 200 K) of PrBa2Cu3-xGaxO7 (x = 0.2) thin films grown by pulsed laser deposition follows the Mott variable range hopping law. The positive lattice mismatch to SrTiO3 (Delta a/a = +0.15%) leads to alternately strained pseudomorphic superlattices with YBa2Cu3O7, when the elementary layer is ultra-thin (less than or equal to 5 nm). Chemical diffusion of gallium in YBa2Cu3O7/PrBa2Cu3-xGaxO7 heterostructures is neither detected from the refinement calculations of the XRD spectra nor from SIMS profile analysis. The T-c lowering of the superlattices is explained in terms of charge transfer effect. The shortest period superlattices without Josephson coupling between the YBa2Cu3O7 layers (M \textbackslashtextbackslashtextbackslashtextgreater 3, N less than or equal to 4) show Kosterlitz-Thouless bidimensional fluctuations due to the strong anisotropy of the structure.
    Note Note
    <p>Symposium on High Temperature Superconductor Thin Films - Growth Mechanisms, Interfaces, Multilayers, at the 1996 Spring Meeting of the European-Materials-Society, STRASBOURG, FRANCE, JUN 04-07, 1996</p>

  • V. Cros, S. - F. Lee, G. Faini, A. Cornette, A. Hamzic, A. Fert, Detection of the magnetization reversal in submicron Co particles by GMR measurements. Journal of Magnetism and Magnetic Materials. 165, 512–515 (1997).
    Résumé : Co particles were obtained by patterning trilayers such as Co/Cu/Co and NiFe/Cu/Co grown by sputtering. Using electronic lithography, we can design on these layers a microsensor for transport measurements and a Co particle on the top layer. The Co particle and the sublayers form a spin-valve structure due to their different coercivity. We used GMR measurements to detect the magnetization reversal in Co particles with sizes between 100 × 50 μm2 and 180 × 20 nm2. We present the size dependence of the GMR ratio and of the reversal magnetic field. For the smallest size, we do not find a Stoner- Wolfahrt-like rotation (i.e. uniform rotation) of the Co particle magnetization, but GMR displays staircase curves indicating discrete variation of this magnetization.

  • V. Cros, F. Petroff, J. Vogel, A. Fontaine, J. - P. Kappler, G. Krill, A. Rogalev, J. Goulon, Palladium magnetism in Pd/Fe multilayers studied by x-ray magnetic circular dichroism at the Pd L2,3 edges (abstract). Journal of Applied Physics. 81, 3774 (1997).

  • S. Dubois, J. - M. Beuken, L. Piraux, J. - L. Duvail, A. Fert, J. - M. George, J. - L. Maurice, Perpendicular giant magnetoresistance of NiFe/Cu and Co/Cu multilayered nanowires. Journal of Magnetism and Magnetic Materials. 165, 30–33 (1997).
    Résumé : We report a comparative study of the giant magnetoresistance (GMR) in CPP (current perpendicular to the planes) geometry in two different types of multilayered nanowire systems: Co/Cu and Ni80Fe20/Cu. The nanowires were produced in the cylindrical pores of a polymer membrane using a pulsed electrodeposition technique. A GMR ratio as large as 78% was obtained for Ni80Fe20/Cu multilayered nanowires. Using the results of the Valet-Fert model for perpendicular transport, we deduce the bulk and interface spin asymmetry coefficients and comparison is made between the two systems.

  • S. Dubois, J. - L. Duvail, A. Fert, J. - M. George, J. - L. Maurice, L. Piraux, Perpendicular giant magnetoresistance in Co/Cu and permalloy/Cu multilayered nanowires (abstract). Journal of Applied Physics. 81, 4569 (1997).

  • S. Dubois, C. Marchal, J. - M. Beuken, L. Piraux, J. - L. Duvail, A. Fert, J. - M. George, J. - L. Maurice, Perpendicular giant magnetoresistance of NiFe/Cu multilayered nanowires. Applied Physics Letters. 70, 396–398 (1997).
    Résumé : We have prepared by electrodeposition Ni 80 Fe 20 /Cu multilayered nanowires into the pores of polymer membranes and performed giant magnetoresistance(GMR)measurements in the current perpendicular to the layer planes geometry. GMR ratios as high as 80% have been obtained at 4.2 K. Two types of structure have been studied: conventional Ni 80 Fe 20 /Cu multilayers and multilayers composed of Ni 80 Fe 20 /Cu/Ni 80 Fe 20 trilayers magnetically isolated by long Cu rods.

  • V. Dupuis, J. Tuaillon, B. Prevel, A. Perez, P. Melinon, G. Guiraud, F. Parent, L. B. Steren, R. Morel, A. Barthélémy, A. Fert, S. Mangin, L. Thomas, W. Wernsdorfer, B. Barbara, From the superparamagnetic to the magnetically ordered state in systems of transition metal clusters embedded in matrices. Journal of Magnetism and Magnetic Materials. 169, 42–45 (1997).
    Résumé : One of the interests in systems of ultrafine particles embedded in matrices is to adjust the size of the nanoparticles and the mean distance between them separately to study cluster interactions in a controlled environment. The synthesis of iron and cobalt clusters embedded in an insulating or metallic matrix has been realized by the co-deposition of both beams arriving at the same time on a 45°-tilted substrate. The nanoparticles were produced from an intense cluster beam of selected size (centered around 300 atoms per cluster) produced from a laser vaporization source. We used a Knudsen cell to evaporate the matrix. From the ratio of the deposition rates of both beams, we were able to continuously adjust the atomic concentrations of the clusters in the matrix from 3 to 70%. In situ electrical conductivity measurements confirmed a 3D percolation threshold of around 25%. The typical size distribution of embedded clusters determined from HRTEM observations revealed nanocrystallized grains with a very narrow dispersion in size. Two local environments emerge from EXAFS simulations: core atoms in the cluster with the density of bulk and surface atoms with a dilated parameter. In agreement with structural considerations, we clearly observed by magnetoresistance and magnetization measurements versus temperature and concentration a magnetic percolation threshold of around 25% for Co clusters in a Ag matrix (maximum of 12% GMR) corresponding to the transition from the superparamagnetic to the magnetically ordered state.

  • J. Durrell, G. Hauchecorne, J. Bok, J. Bouvier, A. - C. Boccara, J. - P. Contour, J. - P. Roger, Study of the birefringence by optical reflectivity in YBa2Cu3O7 and its variation with a superconducting current. Physica C: Superconductivity. 282, 1025–1026 (1997).
    Résumé : The birefringence of c-axis thin films of YBa2Cu3O7 has been evaluated by the change in polarization of reflected light. It has been observed that the flow of an electric current through superconducting YBCO thin film induces an increase in the optical birefringence. That is tentatively explained by a the shift of the oxygens in the chains. The polarization and the complex refractive index have been computed as a function of the shift of the O atoms: the result is in good agreement with the experimental relative phase difference.
    Note Note
    <p>International Conference on Materials and Mechanisms of Superconductivity - High Temperature Superconductors V, BEIJING, PEOPLES R CHINA, FEB 28-MAR 04, 1997</p>

  • A. Encinas, F. Nguyen Van Dau, M. Sussiau, A. Schuhl, P. Galtier, Contribution of current perpendicular to the plane to the giant magnetoresistance of laterally modulated spin values. Applied Physics Letters. 71, 3299–3301 (1997).
    Résumé : Giant magnetoresistance(GMR)effects up to 10% have been observed in Co/Cu/FeNi spin valve structures grown onto step bunched vicinal Si(111) substrates misoriented towards [11-2]. The step bunching is activated using a simple thermal treatment which leads to surfaces where terraces alternate with facets at the nanometer scale. GMR of the spin valve structures is investigated with the current applied parallel or perpendicular to the steps. An in-plane uniaxial magnetic anisotropy is induced in each magnetic layer with the easy axis parallel to the steps. This results in square GMR behavior when the field is applied along the easy axis. Specific features observed when the field is applied along the hard axis are also shown to be the consequence of this anisotropy. When the initial misorientation angle of the substrate becomes higher than 4°, we observe an enhancement of the room-temperature GMR when the current is applied perpendicular to the steps. The origin of this enhancement is discussed based on the temperature dependence of this effect.

  • R. Ferré, K. Ounadjela, J. - M. George, L. Piraux, S. Dubois, Magnetization processes in nickel and cobalt electrodeposited nanowires. Physical Review B. 56, 14066–14075 (1997).

  • A. Fert, S. - F. Lee, Spin injection: theory and application to Johnson's spin switch. Journal of Magnetism and Magnetic Materials. 165, 115–120 (1997).
    Résumé : We apply the formalism of the model worked out by Valet and Fert for perpendicular transport in multilayers to the problem of Johnson's spin switch. We find that, when the spin relaxation in the ferromagnetic layers is taken into account, the output voltage does not diverge when the nonmagnetic thickness tends to zero, but tends to a constant value governed by the spin relaxation in the ferromagnet. We also find that there is complete correspondence between the theoretical expressions for Johnson's spin switch and CPP-MR of multilayers. However, comparing and discussing experimental results on spin switch and CPP-MR structures leads to the puzzling result that the spin diffusion lengths required to account for spin switch data are much larger than those derived from CPP-MR measurements.

  • A. Fert, R. Morel, A. Barthélémy, V. Cros, J. - L. Duvail, J. - M. George, F. Parent, F. Petroff, C. Vouille, Magnétorésistance géante dans les nanostructures magnétiques. Le Journal de Physique IV. 07, C6–151–C6–161 (1997).

  • A. Filipe, H. - J. Drouhin, G. Lampel, Y. Lassailly, J. Peretti, V. I. Safarov, A. Schuhl, dans Symposium M – Magnetic Ultrathin Films, Multilayers, and Surfaces – 1997 (1997)vol. 475 of MRS Online Proceedings Library Archivep. .
    Résumé : ABSTRACTWe observe spin-dependent transmission of hot electrons through the ferromagnetic metallic layer of a Schottky diode. A 25% spin-polarized electron beam is produced in vacuum by a GaAs photocathode under illumination with circularly polarized light. The photoemitted electrons are then injected from the vacuum into the sample: a 3.5 nm-thick Fe layer deposited on a n-doped GaAs substrate. We measure a transmission coefficient of the order of a few 10-4. Using an incident energy above the Fermi level equal to 5 eV, a 5% asymmetry in the transmitted current is observed by changing the spin-polarization of the incident electrons (i.e. the light polarization) and/or reversing the Fe-layer magnetization. This corresponds to a transmission spin-dependence of 20% for a 100% spin-polarized incident beam.

  • A. Filipe, A. Schuhl, Magnetism of Fe thin layers on GaAs (001). Journal of Applied Physics. 81, 4359–4361 (1997).
    Résumé : We study the magnetic properties of Fe thin films epitaxially grown on GaAs (001) for a large range of substrate temperature. Magnetization deficiency has been detected and studied. Its dependence with both thickness and temperature clearly show the existence of a nearly half-magnetized phase at the interface, covered by “as-bulk” Fe. In order to inhibit this interdiffusion, we study several methods. Using previous O 3 oxidation of GaAs, the Fe layer is fully magnetized even for deposition at 200 °C.

  • A. Filipe, A. Schuhl, P. Galtier, Structure and magnetism of the Fe/GaAs interface. Applied Physics Letters. 70, 129–131 (1997).
    Résumé : We study the magnetic properties of Fe thin films epitaxially grown on GaAs (001) for a large range of substrate temperature. Magnetization deficiency has been observed and studied. Its dependence on both thickness and temperature clearly show the existence of a nearly half-magnetized phase at the interface, covered by “as-bulk” Fe. Furthermore, reflection high-energy electron diffraction studies show a transition between two bcc structures with different crystalline parameters. Transmission electron microscopy confirms the formation of this interfacial phase, for which the compound Fe 3 Ga 2−x As x seems to be the best candidate.

  • S. Y. Hsu, A. Barthélémy, P. Holody, R. Loloee, P. A. Schroeder, A. Fert, Towards a Unified Picture of Spin Dependent Transport in and Perpendicular Giant Magnetoresistance and Bulk Alloys. Physical Review Letters. 78, 2652–2655 (1997).
    Résumé : From data on (Fe1−xVx/Cu/Co/Cu)N multilayers, we show that Fe doped with V gains a negative spin asymmetry for bulk scattering (β\textbackslashtextbackslashtextless0), which, combined with the positive asymmetry of Co, accounts for the inverse current perpendicular to the plane (CPP) giant magnetoresistance (GMR) we observe. More precisely, the competition between positive and negative asymmetries for interface and bulk scatterings in FeV leads to inverse (normal) GMR for layers thicker (thinner) than a compensation thickness. The negative β of FeV is consistent with theoretical predictions and bulk alloy data. The current in the plane (CIP) GMR is not reversed, which illustrates the role of channeling in CIP.

  • Y. Lemaitre, D. Mansart, B. Marcilhac, J. Garcia-Lopez, J. Siejka, J. - C. Mage, Evidence of a “notch effect” in microwave surface resistance versus deposition temperature for Y1Ba2Cu3O7−x thin film on MgO (100) substrate. Journal of Alloys and Compounds. 251, 166–171 (1997).
    Résumé : The effect of deposition temperature of Y1Ba2Cu3O7−x thin film on the microwave surface resistance Rs has been studied for films deposited in-situ by cathodic sputtering on MgO (100) single crystal substrate and compared to results obtained on LaAlO3 (100) single crystal substrates. The measurements of Rs were performed at 10 GHz and 77 K using the dielectric resonator method. It was found that YBa2Cu3O7−8 films where Rs values are lower than 0.5 mΩ were obtained on MgO substrate within an extremely narrow temperature range (1–2 °C). The presence of the lowest Rs values were found to be correlated with the lowest RBS yield in channelling geometry (χmin) and with the lowest quantity of misaligned c-axis grains.

  • J. - L. Maurice, P. Schwander, F. H. Baumann, A. Ourmazd, Real-space analysis of lattice images and its link to conventional theory. Ultramicroscopy. 68, 149–161 (1997).
    Résumé : We show that real-space analysis of lattice images in terms of multidimensional vectors rests on a small number of physically significant dimensions, each representing the contribution of a characteristic pattern forming a basis vector. In many cases, these basis vectors can be linked to “spatial periodicities”, and expressed in terms of conventional formalisms of dynamical scattering. This provides a link between the more abstract (but convenient) real-space image analysis and the more familiar formalisms of image formation in terms of Bloch waves. Within this framework, the simplest implementations of QUANTITEM and Chemical Mapping may be viewed as limiting cases of a more general approach. This helps delineate the application domain for each. The paper is illustrated by reference to the AlxGa1 − xAs system in the 〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉 projections. The historically popular 〈1 1 0〉 projection is shown to be the most complex for quantitative data extraction.

  • J. Nassar, M. Viret, M. Drouet, J. - P. Contour, C. Fermon, A. Fert, dans Symposium V – Science & Technology of Magnetic Oxides (1997)vol. 494 of MRS Online Proceedings Library Archivep. .
    Résumé : ABSTRACTLarge magnetoresistance values are obtained on tunnel junctions epitaxially deposited by pulsed-laser deposition and consisting of ferromagnetic manganite La0.67Sr0.33MnO3 electrodes separated by various tunnel barriers: SrTiO3, PrBaCu2.8Ga0.2O7 and CeO2. The magnetoresistance can be decomposed into a low-field and a high-field contribution. The latter is attributed to the presence of canted interfacial manganite phases, as confirmed by the temperature behaviour of the resistance. A low-field magnetoresistance ratio of 450% below 100 Oe is obtained on a sample with a SrTiO3 barrier, indicating a spin polarization value in excess of 0.83 for the manganite.

  • F. Nguyen Van Dau, M. Sussiau, A. Schuhl, P. Galtier, Magnetic thin films having a lateral nanostructural periodicity. Journal of Applied Physics. 81, 4482–4484 (1997).
    Résumé : Magnetic and magnetoresistive properties of thin filmsdeposited on periodically structured substrates are studied. We used a thermodynamical heat treatment to activate the step bunching phenomena on vicinal Si(111) substrates misoriented towards [112̄]. Then, Co or FeNi magnetic layers have been grown, with thicknesses ranging between 20 and 100 Å. Transmission electron microscopy experiments reveal a lateral pseudoperiodic variation of the epitaxial relationship of the metallic layers. Magnetometry measurements reveal an in-plane uniaxial magnetic anisotropy with the easy axis parallel to the step direction. We discuss the relative contributions of magnetocrystalline and shape effects to the anisotropy. Surprisingly, the angular dependance of the anisotropic magnetoresistance reveal a single-domain behavior and a magnetization reversal by rotation, with an active area as large as 700 μm×100 μm. We discuss the influence of the magnetic layer thickness on the magnetization reversal process.

  • K. Ounadjela, R. Ferré, L. Louail, J. - M. George, J. - L. Maurice, L. Piraux, S. Dubois, Magnetization reversal in cobalt and nickel electrodeposited nanowires. Journal of Applied Physics. 81, 5455 (1997).

  • G. Palasantzas, J. Barnas, Surface-roughness fractality effects in electrical conductivity of single metallic and semiconducting films. Physical Review B. 56, 7726–7731 (1997).
    Résumé : Surface-roughness effects in electrical conductivity of thin metallic and semiconducting films with self-affine fractal surfaces are considered in the framework of the Born approximation. The surface roughness is described by the k-correlation model, and is characterized by the roughness exponent H (0 less than or equal to H less than or equal to 1), the in-plane correlation length xi, and the rms roughness amplitude Delta. In the case of metallic films the conductivity is shown to increase monotonically with H increasing from H=0 to H=1 and with decreasing ratio Delta/xi. For semiconducting quantum wells the conductivity shows a peculiar interplay of quantum-mechanical effects and scattering due to surface roughness.

  • F. Parent, J. Tuaillon, L. B. Stern, V. Dupuis, B. Prevel, A. Perez, P. Melinon, G. Guiraud, R. Morel, A. Barthélémy, A. Fert, Giant magnetoresistance in Co-Ag granular films preparedby low-energy cluster beam deposition. Physical Review B. 55, 3683–3687 (1997).
    Résumé : In this paper, we report on structural, magnetic, and magnetoresistive properties of Co-Ag granular films made by low-energy cluster beam deposition (LECBD). With this technique, we can grow granular films of cobalt clusters embedded in silver or other matrix materials, with independent control of the size and concentration of the clusters. Moreover, we show, from TEM, grazing-incidence small-angle x-ray diffraction, and magnetic measurements, that the size of the clusters is the same, whatever the matrix. We measured the giant magnetoresistance (GMR) and magnetic properties of cobalt clusters in silver, and found them similar to those of granular alloys made by codeposition of atoms. Then, taking advantage of the independent control on the size and distribution of the clusters allowed with LECBD, we studied the concentration dependence of the GMR. Its variation at low cobalt content seems to indicate that GMR in the granular geometry is intermediate between CIP and CPP.

  • F. Petroff, L. - F. Schelp, S. - F. Lee, F. Fettar, P. Holody, A. Vaurès, J. - L. Maurice, A. Fert, Spin-dependent tunneling in granular magnetic tunnel junctions. Journal of Magnetism and Magnetic Materials. 175, 33 (1997).

  • L. Piraux, S. Dubois, E. Ferain, R. Legras, K. Ounadjela, J. - M. George, J. - L. Maurice, A. Fert, Anisotropic transport and magnetic properties of arrays of sub-micron wires. Journal of Magnetism and Magnetic Materials. 165, 352–355 (1997).
    Résumé : We report a comparative study of anisotropic magnetoresistance and magnetic properties in arrays of sub-micron Ni and Co wires electro-deposited in the cylindrical pores of track-etched polymer membranes. The variation of coercivity and squareness as a function of wire diameter for arrays of almost isolated sub-micron wires is reported in the range 30–500 nm. The Ni and Co-based systems demonstrate different magnetic and magnetoresistive behaviors except for the smallest diameter. It is believed that the observed difference originates from the presence of competing crystal anisotropy in the Co-based system.

  • K. Postava, H. Jaffrès, A. Schuhl, F. Nguyen Van Dau, M. Goiran, A. - R. Fert, Linear and quadratic magneto-optical measurements of the spin reorientation in epitaxial Fe films on MgO. Journal of Magnetism and Magnetic Materials. 172, 199–208 (1997).
    Résumé : We have undertaken a detailed study by magneto-optical techniques of in-plane magnetization reversal behaviour in epitaxial Fe films grown by MBE on (10 0) oriented MgO substrate. We measure MH loops for both orthogonal in-plane magnetization components Mt (component parallel to the magnetic field) and Mt (component perpendicular to the field) and for various orientations of the magnetic field with respect to the crystalline axis. These measurements show the classical four-fold cubic anisotropy for large Fe film thickness and confirm the appearance of weak uniaxial in-plane anisotropy superimposed for thinner films (t = 20 Å). We have demonstrated the appearance of strong asymmetrical hysteresis loop for p-polarized incident light. We explain this behaviour as the mixing of transverse magnetization contribution to the longitudinal magnetization measurements on the basis of quadratic magneto-optical effects. The calculation of these effects based on eigenmode propagation in anisotropic layered media are developed by including the second-order magneto-optical terms in the permittivity tensor characteristic of a cubic crystal. The second-order reflection coefficients are discussed in the case of the normal incidence of the laser beam and for the magnetic field along the hard axis of the Fe film.

  • L. Ressier, H. Jaffrès, A. Schuhl, F. Nguyen Van Dau, M. Goiran, J. - P. Redoules, J. - P. Peyrade, A. - R. Fert, dans Symposium M – Magnetic Ultrathin Films, Multilayers, and Surfaces – 1997 (1997)vol. 475 of MRS Online Proceedings Library Archivep. .
    Résumé : ABSTRACTThe method has been successfully used to cut a Fe thin film, epitaxially grown onto a (001) MgO substrate, into stripes (widths ranging from 1 μm to 100 nm) and boxes (lateral sizes ranging from 1 μm to 3 μm). A structural analysis of these magnetic structures by atomic force microscopy has shown that their geometries are controlled by the plastic strain. A magnetooptical study of the Fe stripes has revealed a surprising uniaxial magnetic anisotropy with an in-plane easy axis perpendicular to the stripes. This strong anisotropy can be explained by an anisotropie relaxation of the misfit between the starting Fe film and the MgO substrate, induced by the cutting into stripes. Magnetooptical experiments on boxes have revealed that the initial cubic symmetry is recovered since, in this case, the relaxation is similar in perpendicular directions. They have also proved that their magnetization reversal is governed by nucleation phenomena.

  • L. Ressier, A. Schuhl, F. Nguyen Van Dau, K. Postava, M. Goiran, J. - P. Peyrade, A. - R. Fert, Strong uniaxial magnetic anisotropy of nanostripes obtained by cutting thin epitaxial Fe layer using the atomic saw method. Journal of Applied Physics. 81, 5464–5466 (1997).
    Résumé : We have applied the “atomic saw” method developed on semiconductorheterostructures to cut thin epitaxial Fe filmsdeposited on (001) MgO substrate into Fe nanostripes. This method is based on dislocation slipping. We have controlled the slip along the (110) MgO planes and obtained Fe stripes along the [110] direction. We present the magnetic study of 2- and 5-nm-thick Fe films which have been cut by this method, with a deformation up to 8%. The surface of the deformed film, studied by atomic force microscopy, is characterized by regular steps, a few nm high, and from 50 nm to 2 μm wide, depending on the slipping plane density. Strong uniaxial magnetic anisotropy has been observed by magneto-optical measurements. Surprisingly, the easy magnetic axis is perpendicular to the nanostripes. Various possible mechanisms are discussed. However, it results probably in the relaxation of the elastic strain field at the Fe/MgO interface.

  • L. - F. Schelp, A. Fert, F. Fettar, P. Holody, S. - F. Lee, J. - L. Maurice, F. Petroff, A. Vaurès, Spin-dependent tunneling with Coulomb blockade. Physical Review B. 56, R5747–R5750 (1997).

  • L. - F. Schelp, S. - F. Lee, F. Fettar, F. Nguyen van Dau, F. Petroff, A. Vaurès, A. Fert, Spin-dependent tunneling between ferromagnetic metals in a new type of tunnel junction (abstract). Journal of Applied Physics. 81, 5508 (1997).

  • M. Sussiau, A. Encinas, F. Nguyen Van Dau, A. Vaurès, A. Schuhl, P. Galtier, dans Symposium M – Magnetic Ultrathin Films, Multilayers, and Surfaces – 1997 (1997)vol. 475 of MRS Online Proceedings Library Archivep. .
    Résumé : ABSTRACTMagnetic and magnetoresistive properties of magnetic thin films deposited on periodically structured substrates have been studied. By using a thermodynamical heat treatment, we activate the step bunching phenomenon on vicinal Si(111) substrates misoriented towards [112] which results in a laterally modulated surface with a period around 0.1 μm. Epitaxial magnetic thin films deposited on these substrates exhibit an in-plane uniaxial anisotropy and a specific magnetoresistive behavior which characterizes the magnetization reversal process. In this contribution, we demonstrate that these properties can also be observed in non-epitaxial structures grown either by molecular beam epitaxy or by sputtering. In particular, magnetotransport measurements show that by varying parameters such as the nature of the magnetic metal, the layer thickness or the strength of the induced anisotropy, we can modulate the interplay between the anisotropy and the exchange stiffness, and, consequently, observe gradual magnetization reversal behaviors between a Stoner-Wohlfarth uniform mode and a non-uniform mode.

  • M. Sussiau, F. Nguyen Van Dau, P. Galtier, A. Encinas, A. Schuhl, Bicrystalline magnetic lateral superlattices. Journal of Magnetism and Magnetic Materials. 165, 1–4 (1997).
    Résumé : We have studied the correlations between structural, magnetic and transport properties of bicrystalline lateral magnetic superlattices grown by molecular beam epitaxy on vicinal Si(111) substrates misoriented towards [112]. The substrates were thermally pre-treated in order to activate the step bunching phenomena, which results in a laterally modulated surface topology with a period of ≈ 1000 Å and an amplitude up to 80 Å. 100 Å thick Co or FeNi magnetic layers grown on such substrates exhibit an in-plane uniaxial anisotropy with the easy axis parallel to the step direction. Transmission electron microscopy experiments reveal that this anisotropy can be associated with a lateral pseudo-periodic variation of the epitaxial relationship of the metallic layers. Magneto-resistance measurements on a 700 μm × 100 μm active area surprisingly reveal a single-domain behaviour with a magnetization reversal by rotation.
  • W. Szuszkiewicz, M. Jouanne, J. - F. Morhange, M. - A. Kanehisa, H. Mariette, J. - M. Hartmann, E. Dynowska, G. Karczewski, T. Wojtowicz, J. Kossut, J. Barnas, Raman characterization of MBE-grown layered MnTe/CdTe structures. Acta Physica Polonica A. 92, 1021–1024 (1997).
    Résumé : Raman scattering measurements on (MnTe)(8)/(Cd0.64Zn0.36Te)(8) multilayer grown by MBE method and on various (MnTe)(n)/(CdTe)(12) multilayers (where n = 8, 12, 16, 24) were performed at low temperatures. In the (z) over bar(x,x)z polarization, structures corresponding to folded acoustic phonons were found. In (z) over bar(x,y)z polarization new complex structures were observed in the low-frequency part of Raman scattering spectra. A possible magnetic origin of these structures is discussed.
    Note Note
    <p>XXVI International School on Physics of Semiconducting Compounds, JASZOWIEC, POLAND, JUN 06-13, 1997</p>

  • M. Viret, M. Drouet, J. Nassar, J. - P. Contour, C. Fermon, A. Fert, Low-field colossal magnetoresistance in manganite tunnel spin valves. Europhysics Letters. 39, 545–550 (1997).

  • J. Vogel, A. Fontaine, V. Cros, F. Petroff, J. - P. Kappler, G. Krill, A. Rogalev, J. Goulon, Structure and magnetism of Pd in Pd/Fe multilayers studied by x-ray magnetic circular dichroism at the Pd L2,3 edges. Physical Review B. 55, 3663–3669 (1997).
    Résumé : We have measured the L2,3 absorption edges of Pd in Pd/Fe multilayers with different Pd interlayer thicknesses. The spectral features observed after the L3 and L2 white lines indicate that in the atomic layer adjacent to Fe the Pd atoms have a local structure different from fcc. X-ray magnetic circular dichroism (XMCD) at these edges shows that the atoms directly at the interface are strongly polarized with a total moment of about 0.4μB /atom. The orbital moments are found to be small (0.0–0.04μB ). The thickness dependence of the XMCD shows that Pd atoms carry a magnetic moment up to four layers from the interface. The magnetic interface appears larger than the crystallographic one.

  • J. Vogel, A. Fontaine, V. Cros, F. Petroff, J. - P. Kappler, G. Krill, A. Rogalev, J. Goulon, Palladium magnetism in Pd/Fe multilayers studied by XMCD at the PdL2,3 edges. Journal of Magnetism and Magnetic Materials. 165, 96–99 (1997).
    Résumé : We have performed direct measurements of the Pd4d orbital and spin moments in Pd/Fe multilayers with different Pd interlayer thicknesses using X-ray magnetic circular dichroism (XMCD) at the L2,3 absorption edges of Pd. The atoms directly at the interface are strongly polarized with a total moment of 0.4μB/atom. The orbital moments are found to be small (0.0–0.04μB). The thickness dependence of the XMCD shows that Pd atoms are magnetically polarized up to four layers from the interface.

  • C. Vouille, A. Fert, A. Barthélémy, S. Y. Hsu, R. Loloee, P. A. Schroeder, Inverse CPP-GMR in (A/Cu/Co/Cu) multilayers (A=NiCr, FeCr, FeV) and discussion of the spin asymmetry induced by impurities. Journal of Applied Physics. 81, 4573–4575 (1997).
    Résumé : We present CPP-GMR experiments on a series of multilayers of the type (A/Cu/Co/Cu)×N where A is a layer of NiCr, FeCr, or FeV alloys with concentrations of Cr or V between 2.5 and 30 at. %. The inverse GMR effects we observe can be accounted for by the opposite scattering spin asymmetries in Co (positive spin asymmetry) and A (negative spin asymmetry). As the spin asymmetry in A is positive for interface scattering and negative for bulk scattering, the inverse GMR is observed only for thicknesses greater than one at which interface and bulk scattering compensate. We determine the magnitude and sign of the spin asymmetry coefficients, and we notice the agreement with previous data on dilute alloys and with theoretical calculations.

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