Cécile Autret-Lambert

Pulsed laser-deposited VO2 thin films on Pt layers

VO2 films were deposited on Pt (111)/TiO2/SiO2/Si (001) substrates by means of a pulsed laser deposition technique. An x-ray diffraction peak at 2θ = 39.9° was deconvoluted into two pseudo-Voigt profiles of Pt (111) and VOx-originated components. The VOx diffraction peak was more obvious in a VOx/Pt (111)/Al2O3 (0001) sample, having a narrower width compared with a VO2/Al2O3 (0001) sample. Temperature-controlled Raman spectroscopy for the VOx/Pt/TiO2/SiO2/Si sample has revealed the monoclinic VO2 phase at low temperature and the structural phase transition at about 72 °C in a heating process. The electronic conductive nature at the high temperature phase was confirmed by near normal incidence infrared reflectivity measurements. Out-of-plane current-voltage characteristics showed an electric field-induced resistance switching at a voltage as low as 0.2 V for a 50 nm-thick film. A survey of present and previous results suggests an experimental law that the transition voltage of VO2 is proportional to the sq...

Enhancement of piezoelectric response in Ga doped BiFeO3 epitaxial thin films

The piezoelectric properties of compositional spread (1 − x)BiFeO3-xGaFeO3 epitaxial thin films are investigated where Ga3+ substitution for Bi3+ is attempted in Bi1−xGaxFeO3 compounds. Ga content x was varied from 0 to 12% (atomic). Ferroelectric characterizations are reported at various length scales. Around 6.5% of Ga content, an enhancement of the effective piezoelectric coefficient d33eff is observed together with a change of symmetry of the film. Measured d33eff values in 135 nm thick films increased from 25 pm/V for undoped BiFeO3 to 55 pm/V for 6.5% Ga with no extrinsic contribution from ferroelastic domain rearrangement.

Cyclable and non-volatile electric field control of magnetism in BiFeO3 based magnetoelectric heterostructures

Room temperature manipulation of the ferromagnetic state via an electric field is investigated in Ni/BiFe0.95Mn0.05O3 thin film heterostructures. A 600% increase in the magnetic coercive field of the Ni layer is observed at the initial DC electrical poling of the ferroelectric BiFe0.95Mn0.05O3 layer. The magnetoelectric effect is remanent, and the magnetic coercive field can be modulated between a low value and a high value by successively switching the ferroelectric polarization. After the initial poling, the coercive field difference is decreased by subsequent back and forth switching. However, the magnetic bi-stability is preserved at least up to 250 cycles, which is promising for spintronic applications.

Cu-doping effect on dielectric properties of organic gel synthesized Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ}

Abstract Copper doped-Ba 4 Y Mn 3− x Cu x O 11.5± δ samples were synthesized by an organic gel assisted citrate process. X-ray diffraction of compositions with x =0.002, 0.005, 0.01, 0.02 and 0.04 does not reveal any change of hexagonal perovskite structure on doping. The effects of Cu-doping on the microstructure and dielectric properties were investigated. Cu doping modifies the electrical properties at the level of the impedance characteristics of both grain and grain boundary and to understand these different behaviours, we have carried out high-resolution transmission electron microscopy analysis. Among the Ba 4 Y Mn 3− x Cu x O 11.5± δ specimens studied, the composition x =0.002 shows a permittivity ( e ′ r ) higher than the undoped compound and a lower loss tangent (tan δ ) over several orders of magnitude of frequency.

Existence of a solid solution from brucite to {beta}-Co(OH){sub 2}

Abstract This study shows that between brucite (Mg(OH)2) and β-Co(OH)2, all the compositions are possible. The solid solution Mg1−xCox(OH)2 has been synthesized by an easy and fast coprecipitation route and characterized by XRD and TEM. Single phase powders have been obtained. The particles exhibit platelets morphology with a size close to one hundred nanometers. XRD analysis shows an evolution of the cell parameters when x increases and demonstrates that no ordering of the cations occurs. However, extra reflections on TEM electron diffraction patterns seem to indicate that local ordering can exist. The compounds issued from this solid solution could be good candidates as precursors in order to obtain Mg–Co mixed oxide with all possible cationic ratios.