Publications (21)28.32 Total impact
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Article: Room temperature multiferroicity in Ga0.6Fe1.4O3:Mg thin films
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ABSTRACT: We report on the multiferroic behavior of 2%-magnesium-doped Ga0.6Fe1.4O3 thin film at room temperature. The sample was grown by pulsed laser deposition on a Pt-coated Yttrium-Stabilized Zirconia substrate. Magnetic measurements indicate a net magnetization of 105 emu/cm3 at 295 K, and the persistence of magnetic ordering above room temperature. Ferroelectric measurements show clear polarization switching with negligible contribution from leakage currents, with a polarization of 0.2 μC/cm−2 and a coercive field of 133 kV/cm. Scanning probe microscopy confirms the low leakage current and detects a stable piezoelectric signal. This could open original perspectives for the application of single-phased multiferroic systems.Journal of Applied Physics 06/2013; 113(21). · 2.17 Impact Factor -
Article: Nuclear magnetic resonance investigations of the structure and magnetic properties of metallic multilayers and nanocomposites
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ABSTRACT: As a probe of the short-range chemical and topological order, nuclear magnetic resonance (NMR) has proved useful to investigate the nanostructure of magnetic multilayers or granular systems and, in particular, to evaluate the nature, sharp or diffuse, of interfaces in such nanocomposites. These structural aspects are shortly reviewed in the paper. A larger emphasis is given to the magnetic properties that are accessed by the technique. As a first output of an NMR experiment in ferromagnets, the hyperfine field gives a direct insight on the local magnetization. Hence, for example, one can estimate the magnetization profile at a diffuse interface between a magnetic and nonmagnetic phase. In addition, NMR can probe selectively the magnetic anisotropy or exchange energy in different parts of a composite sample. Therefore NMR is a unique tool to investigate the correlation, at a local scale, between the nanostructure and the magnetic properties of a sample. For example, one can evidence the different magnetic hardness of the interface and bulk moments in multilayers, or of the magnetic clusters and alloyed regions in nanogranular alloys. Some relevant results are presented, which have been obtained in the course of investigations of Co-based multilayers, ultrathin films and granular systems.Applied Magnetic Resonance 04/2012; 19(3):447-460. · 0.75 Impact Factor -
Article: How to obtain a magnetic hard-soft architecture by pulsed laser deposition.
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ABSTRACT: In spin valve type systems, one ferromagnetic electrode must be magnetically hard to act as a reference layer while the other electrode must be magnetically soft to act as a sensor or storage layer. This magnetic hard-soft architecture can usually be obtained by four different methods: the use of two ferromagnets with different coercive fields (here CoFe(2) and Ni(80)Fe(20)), the use of an underlayer enhancing the coercive field of one of the two ferromagnets (here Ta and Ru), the use of a ferromagnet coupled to a ferrimagnet or antiferromagnet (here NiO/CoFe(2) and CoFe(2)O(4)/CoFe(2)), or the use of an artificial antiferromagnet (here CoFe(2)/Ru/CoFe(2)). We show that at least the first and the third methods seem to work with pulsed laser deposition in the thermodynamic conditions used.Nanotechnology 12/2007; 18(49):495708. · 3.98 Impact Factor -
Article: Epitaxial thin films of multiferroic GaFeO3 on conducting indium tin oxide (001) buffered yttrium-stabilized zirconia (001) by pulsed laser deposition
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ABSTRACT: Epitaxial films of an alternative multiferroic material, GaFeO3 (GFO), were grown by pulsed laser deposition on yttrium-stabilized zirconia (001) and on conducting buffer layers of indium tin oxide (001). They present a perfect epitaxial growth along the GFO [010] axis and six crystallographic variants in the film’s plane. Their magnetic properties are close to those of the bulk with an out-of-plane [010] hard direction and a Curie temperature of ∼ 200 K. The films did exhibit ferroelectric properties when characterized by electrostatic force microscopy.Applied Physics Letters 11/2007; 91(20):202504-202504-3. · 3.84 Impact Factor -
Chapter: Nuclear Magnetic Resonance in Ferromagnetic Multilayers and Nanocomposites: Investigations of Their Structural and Magnetic Properties
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ABSTRACT: In the past, nuclear magnetic resonance (NMR) studies have proved useful for structural investigations of magnetic multilayers in the direct space and at the atomic scale, complementing standard structural investigations [1]. Actually NMR provides with an original insight into the structural and magnetic characterization of composite nanostructured materials. Indeed the yield of NMR experiments is twofold. On one hand, the NMR spectrum, usually acquired in zero external field, reflects the distribution of hyperfine fields in the sample, and thus gives information about the different chemical configurations and site symmetries in the sample, the different phases, their structure, and their defects. On the other hand, the evolution of the spectral shape against the external field strength and orientation or against the radio frequency field strength probes the magnetic anisotropy or the magnetic stiffness of the electronic moments around the nucleus site, thus providing an information comparable to that given by ferromagnetic resonance (FMR) measurements. Therefore, combining both yields makes it possible to correlate the inhomogeneous magnetic properties of a composite sample to its different structural components [2]. The structural aspects of NMR studies are summarized in the first part of the chapter. Most of the chapter is devoted, though, to the analysis of NMR data in terms of local magnetic properties.12/2005: pages 1493-1498; -
Article: Structural defects in Sr2FeMoO6 double perovskite: Experimental versus theoretical approach
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ABSTRACT: The lower than expected magnetization of imperfect Sr2FeMoO6 (SFMO) double perovskites is usually attributed to the presence of Fe at antisite positions that would be antiferromagnetically coupled to their regular neighbors. However, ab initio calculations suggest strongly that such defective Fe sites would be ferromagnetically coupled and, consequently, the magnetization reduction would originate from other kinds of defects. The magnetic, hyperfine, and structural properties of SFMO perovskites prepared by solid-state reaction under a variety of conditions are reported and correlated with ab initio calculations of the magnetic moments and hyperfine fields of Mo and Fe ions in different local environments (antisites, antisite neighbors, and neighbors of an oxygen vacancy). When plotted against the order parameter the experimental magnetization is found to decrease at a rate of about −7.6μB per Mo–Fe antisite pair as in other previous experiments, where the theoretical calculation predicts −6.56μB per antisite pair if the moments of Fe antisites are antiparallel to the regular Fe moments. Unfortunately, the energy of this configuration is found to be 0.7 eV higher than that of the parallel configuration for which the magnetization reduction is only −0.19μB per antisite pair. Sources for the supplementary reduction of magnetization have then been considered. The presence of spurious phases cannot account for the observation. Oxygen vacancies do reduce significantly the magnetization (−2.00 μB/vacancy), but no significant sign of their effect is found in the Fe Mössbauer and Mo nuclear magnetic resonance spectra. Moreover, the position of the spectral lines of defects are compatible with the theoretical findings for Fe antisites in the antiparallel spin configuration.Journal of Applied Physics 08/2005; 98(3):033905-033905-11. · 2.17 Impact Factor -
Article: Room-temperature ferromagnetism in Zn1−xCoxO magnetic semiconductors prepared by sputtering
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ABSTRACT: We have used magnetron cosputtering to grow Zn1−xCoxO magnetic dilute semiconductors. The growth has been performed on SiO2/Si and Al2O3(0001) substrates. The Co concentration has been varied between 0.1 and 0.25 and the substrate temperature between room temperature and 600 °C. X-ray diffraction analysis has shown that for the films grown on Si substrates the structural quality of the film is improved by increasing the growth temperature and/or postgrowth annealing. The films are textured with c axis of the wurtzite structure along the growth direction. However, for the films grown on Al2O3 substrate quasi-epitaxial films have been obtained for 600 °C substrate temperature. Magnetization measurements have shown that the ferromagnetism is directly correlated to the structural quality and appears by increasing the growth temperature and/or postgrowth annealing. Moreover, for the highly textured film a clear magnetic perpendicular anisotropy has been evidenced with the easy magnetization axis along the growth direction. To evidence the intrinsic nature of the ferromagnetism in the films, transmission optical measurements have been used. They show three absorption bands that are characteristics of d-d transitions of tetrahedrally coordinated Co2+. This has been supported by nuclear magnetic resonance and magnetic thermal variation.Journal of Applied Physics 06/2005; 97(12):123908-123908-5. · 2.17 Impact Factor -
Article: Magnetic, transport and structural properties of Co/Ir multilayers grown by molecular beam epitaxy
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ABSTRACT: We report on the structural properties of a [Co30/Ir10]10× (Å) superlattice, as well as on the magnetic and transport properties of a Co15/Ir5/Co30 (Å) artificial ferrimagnetic system. The samples were grown by molecular beam epitaxy (MBE) on MgO(001) substrates covered with a Ir130 (Å) buffer layer. High resolution cross section and plan view transmission electron microscopy (TEM) images present a high quality epitaxial stack [100]MgO(001) ‖ [100]Ir(001) ‖ [100]Co(001), with a tetragonalization of the Co fcc structure, due to strains induced by the Ir buffer. TEM images also show that the Co/Ir interfaces are flat, while the layers are continuous and free of bridges. These observations are consistent with zero field nuclear magnetic resonance measurements which indicate an fcc structure of the Co layers, and an interface mixing between Co and Ir limited to one atomic layer. As a consequence the antiferromagnetically coupled Co/Ir/Co sandwich presents large saturation and coercive fields which exceed 20 kOe and 220 Oe, respectively. Annealing made on the same sandwich indicate that the magnetic and transport properties are stable up to 300 °C. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)physica status solidi (a) 09/2003; 199(2):161 - 168. · 1.21 Impact Factor -
Article: Electrodeposited cobalt films: hcp versus fcc nanostructuring and magnetic properties
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ABSTRACT: The crystallographic structure and morphology of electrodeposited cobalt films on Au(111) is found to be very sensitive on the electrolyte pH value and on the overpotential applied during deposition. The samples, 2 to 500 nm thick, where characterized by nuclear magnetic resonance (NMR), atomic force microscopy (AFM) and electron diffraction. The latter technique shows that the Co films grow in registry with the gold underlayer, reproducing the Au(111) texture. During the first stage of growth and depending on overpotential and pH value, either continuous hcp Co films or hcp Co islands are formed. Only the latter growth mode leads to an out of plane magnetization with 100% of remanence. Increasing the thickness, fcc Co becomes the prevailing phase. Eventually the fcc to hcp ratio saturates at the same value regardless the overpotential. The thickness for which the equilibrium fcc to hcp ratio is obtained as well as the sample structure and morphology before saturation, depend strongly on the overpotential value. In any case, the predominance of the fcc Co phase leads to an in plane magnetization of the thick samples. This study opens up new opportunities of engineering the properties of electrodeposited cobalt films.Physics of Condensed Matter 09/2000; 17(4):635-643. · 1.53 Impact Factor -
Article: The anisotropic first-neighbour contribution to the hyperfine field in hexagonal-close-packed Co: a nuclear magnetic resonance study of diluted alloys and multilayers
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ABSTRACT: NMR has been studied in CoCr, CoRu, CoMn and CoCu hexagonal alloys with impurity concentrations below 1 at.% and in two-dimensional alloys present at the interfaces of the corresponding Co/M multilayers, where Co adopts the hcp structure. Two low-frequency satellites have been observed for all of the alloys studied, whereas only one is observed for cubic alloys. Their origin is related to the presence of two inequivalent sites in the first coordination shell of Co, because hcp Co departs from the ideal compact structure. From the results on Co/Cr and Co/Ru multilayers it is deduced that the impurity neighbours out of the c-plane depress the Co hyperfine field less than the in-plane impurity neighbours. Comparison with the alloys CoCr and CoRu suggests a similar conclusion for CoMn alloys. As to CoCu systems, the situation is the opposite, although there is some ambiguity in the analysis of hcp Co/fcc Cu multilayers, because Co might be stacked in a fcc structure at the interface with Cu.Journal of Physics Condensed Matter 12/1998; 10(22):4919. · 2.55 Impact Factor -
Article: Overpotential driven perpendicular magnetization of electrodeposited ultrathin cobalt films
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ABSTRACT: Depending on the overpotential applied during electrodeposition of ultrathin cobalt films (η = 0.1–2.2 V), either in-plane or out-of-plane magnetization can be stabilized. The regime of high supersaturation in particular allows to engineer electrodeposited cobalt films on Au(111) that show perpendicular magnetization (in the thickness range from 2 to 8 atomic layers) exactly like their ultrahigh vacuum grown counterparts. The film topography depends on the overpotential as shown by atomic force microscopy: continuous films are obtained at low overpotential whereas high overpotential leads to the formation of islands. The perpendicular magnetization results from a subtle thickness dependent competition between the shape and the interface anisotropy. © 1998 American Institute of Physics.Journal of Applied Physics 05/1998; 83(11):7043-7045. · 2.17 Impact Factor -
Article: Structural properties and oscillatory magnetoresistance of Co(hcp)/Cu sandwiches
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ABSTRACT: We present structural and magnetoresistance studies for a series of Co(hcp)/Cu sandwiches. RHEED patterns obtained during growth indicate a hcp structure for at least the first Co layer. NMR measurements show a single resonance peak at a frequency of 228 MHz, clearly confirming the hcp structure of both Co layers. The occurrence of the hcp phase for the Co atoms is mainly due to the growth of a thin 8 Å Cu seed layer on the Ru buffer layer. We performed magnetoresistance studies at room temperature and found oscillatory behaviour of the magnetoresistance with a period of about 13 Å, which is smaller than the values usually observed for fcc (111)Co/Cu systems. The magnetoresistance value at the first maximum reaches 4% at room temperature, which indicates the good quality of these samples.Journal of Magnetism and Magnetic Materials. -
Article: Structural properties of electrodeposited Co/Cu multilayers
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ABSTRACT: Co/Cu multilayers have been grown by electrodeposition using a potentiostatic technique in a single electrolyte bath based on CoSO4, H3BO3 and CuSO4. X-ray diffraction performed on these multilayers have shown polycrystalline fcc structure of both Co and Cu layers with preferential (111) texture. Nuclear magnetic resonance spectrum has been recorded at 4.2 K on [Co(6 nm)/Cu(4 nm)]25 and has shown a resonance line at 216 MHz which confirms the fcc structure of Co layers. The analysis of the spectrum showed on one hand that the Co layers are not pure and contain approximately 1.5% of Cu, but on the other hand, the interfaces are of good quality. A cross-sectional on transmission electron micrograph showed a columnar growth morphology. Resistivity measurements performed on this sample presented a giant magnetoresistance (GMR) effect of about 4% at room temperature.Thin Solid Films. -
Article: NMR investigations of the nanostructure of … /Cu/Co/Cu/ … layers
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ABSTRACT: Layered … /Cu/Co/Cu … of various origins have been investigated by NMR. The paper reports on the influence of different preparation techniques (UHV evaporation, dc magnetron or rf diode sputtering), of different buffer layers and of Co and Cu thickness on the bulk and interface atomic structure of the Co layers.Journal of Magnetism and Magnetic Materials 126:16-18. · 1.78 Impact Factor -
Article: Growth and properties of electrodeposited cobalt films on Pt/Si(100) surface
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ABSTRACT: In this paper, the growth, structural and magnetic properties of cobalt (Co) films electrodeposited on a Pt/Si(1 0 0) substrate have been investigated. Co films with metallic appearance were obtained from aqueous solution of 0.1 M CoSO4, 10 mM CoCl2 as the source of metal ions and 1 M Na2SO4 as a supporting electrolyte with 0.5 M H3BO3 at pH 4.2. This electrochemical technique indicated a deposition peak signature of limited diffusion growth with the transition from progressive to instantaneous nucleation mechanism. The atomic force microscopy (AFM) images showed a granular structure of the electrodeposited layers. X-ray measurements (XRD) and nuclear magnetic resonance (NMR) indicate a small grain size with the presence of a mixture of Co hcp and fcc structures. The magnetic properties of the deposited films were investigated with a magnetic field in the parallel and perpendicular direction and showed that the easy magnetization axis is in the plane.Applied Surface Science 228:320-325. · 2.10 Impact Factor -
Article: Structural study of CoFe2/CoFe2O4 multilayers
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ABSTRACT: The study of the CoFe2/CoFe2O4 system is of great interest due to its potential integration in magneto-resistive devices. CoFe2/CoFe2O4 multilayers were elaborated by plasma oxidation of sputtered CoFe2 layers. Exclusive attention is paid, in this paper, to the study by high resolution transmission electron microscopy of the crystallographic relationships between the metal and the oxide networks. The oxide was observed to grow epitaxially from the metal with the following relationship : oxide (1 0 0)[1 0 0] ∥ metal (1 0 0)[1 1 0]. This epitaxial relationship was observed even though the metal (CoFe2 alloy) did not always present its (1 0 0) face to the surface and was oxidised by the violent process that is plasma oxidation. Our conclusion that the growth of epitaxial metal/oxide multilayers by sputtering only depends on the epitaxial growth of the first deposited metal layer is of major interest.Surface Science. 529:215-222. -
Article: Pulsed laser deposition of cobalt ferrite in a reactive O2:N2 atmosphere: effect of the deposition pressure and temperature
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ABSTRACT: Thin films of CoFe2O4 have been fabricated by pulsed laser ablation of a metallic CoFe2 target at two different temperatures (200 and 400 °C) and in various O2:N2, 20:80 pressures [from 0.7 Pa (5×10-3 Torr) up to 26.7 Pa (2×10-1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe2O4. A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe2O4 films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe2O4 films were, respectively, 200 °C and 6.7 Pa.Thin Solid Films 471:40-47. · 1.89 Impact Factor -
Article: Correlation between magnetic properties and nuclear magnetic resonance observations in Sr2FeMoO6 double perovskite
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ABSTRACT: We present the influence of the sintering temperature on the magnetic properties of Sr2FeMoO6 double perovskite, on the basis of magnetization and nuclear magnetic resonance (NMR) measurements. Interestingly, the saturation magnetization originating mainly from the Fe moments is correlated with the amount of Mo magnetic moments observed by NMR measurements. We show that there is an optimum temperature of 1000°C for which the reaction leading to the double perovskite becomes more advanced and/or the number of antisite defects is minimum.Journal of Magnetism and Magnetic Materials. -
Article: Room-temperature ferromagnetism in ZnCoO magnetic semiconductors prepared by sputtering
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ABSTRACT: We have used magnetron cosputtering to grow Zn 1−x Co x O magnetic dilute semiconductors. The growth has been performed on SiO 2 / Si and Al 2 O 3 0001 substrates. The Co concentration has been varied between 0.1 and 0.25 and the substrate temperature between room temperature and 600 ° C. X-ray diffraction analysis has shown that for the films grown on Si substrates the structural quality of the film is improved by increasing the growth temperature and/or postgrowth annealing. The films are textured with c axis of the wurtzite structure along the growth direction. However, for the films grown on Al 2 O 3 substrate quasi-epitaxial films have been obtained for 600 ° C substrate temperature. Magnetization measurements have shown that the ferromagnetism is directly correlated to the structural quality and appears by increasing the growth temperature and/or postgrowth annealing. Moreover, for the highly textured film a clear magnetic perpendicular anisotropy has been evidenced with the easy magnetization axis along the growth direction. To evidence the intrinsic nature of the ferromagnetism in the films, transmission optical measurements have been used. They show three absorption bands that are characteristics of d-d transitions of tetrahedrally coordinated Co 2+ . This has been supported by nuclear magnetic resonance and magnetic thermal variation. © 2005 American Institute of Physics. -
Article: Structure and oscillatory magnetoresistance of Co(hcp)Cu sandwiches
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ABSTRACT: We present structural and magnetoresistance studies performed on a series of sandwiches. We report reflection high-energy electron diffraction analysis and nuclear magnetic resonance measurements showing clearly the hcp structure of the Co layers and we find an oscillatory behaviour of the magnetoresistance with a period of about 13 Å.Thin Solid Films.
Top co-authors
Top Journals
Institutions
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1998–2012
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Institut de Physique et Chimie des Matériaux de Strasbourg
Strasbourg, Alsace, France
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2007
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Ewha Womans University
Seoul, Seoul, South Korea
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2005–2007
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French National Centre for Scientific Research
Lyon, Rhone-Alpes, France
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