Showing papers by "Marc Respaud published in 1999"
TL;DR: The reaction of Ni(COD)2 with H2 (3 bar) in CH2Cl2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of ≈30 nm, composed of individual 3−4 nm fcc Ni particles.
Abstract: The reaction of Ni(COD)2 with H2 (3 bar) in CH2Cl2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of ≈30 nm, composed of individual 3−4 nm fcc Ni particles an...
231 citations
TL;DR: Very small nanometric oxide particles (CoO and Co3O4, around 2 nm in diameter) well dispersed inside a polymer matrix were prepared by solid-state oxidation of a metallic colloid precursor (1.6 nm).
Abstract: Very small nanometric oxide particles (CoO and Co3O4, around 2 nm in diameter) well dispersed inside a polymer matrix were prepared by solid-state oxidation of a metallic colloid precursor (1.6 nm ...
156 citations
TL;DR: In this paper, the authors derived the dynamical susceptibility of the system on the basis of an independent-grain model by using a rectangular approach and showed that the magnetic anisotropy is enhanced compared to the bulk value, and increases as the particle size decreases.
Abstract: We report on high-frequency (300-700 GHz) ferromagnetic resonance (HF-FMR) measurements on cobalt superparamagnetic particles with strong uniaxial effective anisotropy. We derive the dynamical susceptibility of the system on the basis of an independent-grain model by using a rectangular approach. Numerical simulations give typical line shapes depending on the anisotropy, the gyromagnetic ratio, and the damping constant. HF-FMR experiments have been performed on two systems of ultrafine cobalt particles of different sizes with a mean number of atoms per particles of 150 +/- 20 and 310 +/- 20. In both systems, the magnetic anisotropy is found to be enhanced compared to the bulk value, and increases as the particle size decreases, in accordance with previous determinations from magnetization measurements. Although no size effect has been observed on the gyromagnetic ratio, the transverse relaxation time is two orders of magnitude smaller than the bulk value indicating strong damping effects, possibly originating from surface spin disorders.
53 citations
TL;DR: In this article, the authors investigated the magnetic moment of noninteracting cobalt nanoparticles dispersed in a polymer and estimated the relaxation time of the magnetisation associated to the superparamagnetic properties of the particles.
Abstract: The dynamical properties of the magnetic moment of non-interacting cobalt nanoparticles dispersed in a polymer were investigated by ac-susceptibility (10 Hz < f < 104 Hz). We thus estimated the relaxation time of the magnetisation (τ) associated to the superparamagnetic properties of the particles. τ was found to follow the general Neel-Brown relaxation dynamics, with a pre-exponential relaxation time τ0 of 4(±2)·10−12 s for temperatures between 10 and 20 K. By combining the experimental results from ferromagnetic resonance, ac-susceptibility, and magnetisation, measurements giving the microscopic and macroscopic parameters, we demonstrate for the first time that the Coffey theoretical expressions were able to predict both τ and τ0 values. Finally, the thermal dependence of τ0 is discussed.
15 citations
TL;DR: The results of Shubnikov-de Haas (SdH) oscillation measurements on p-CoSb3 single crystals are presented in this paper, where the values of the cyclotron effective mass were determined.
Abstract: The results of Shubnikov–de Haas (SdH) oscillation measurements on p-CoSb3 single crystals are presented. The values of the cyclotron effective mass were determined. It was found that the effective mass increases from 0.11 m 0 to 0.15 m 0 with increasing hole concentration, indicating a non-parabolicity of the valence band of CoSb3. Using the two-band Kane model a band-edge effective mass of mn/m0=0.050±0.002 and an energy gap Eg=35±2 meV were estimated.
12 citations
TL;DR: In this paper, the authors focused on selected H-T phase diagrams and compared the results on Pr1/2Ca 1/2MnO3 with the ideal 1:1 electron/hole ratio, where the carrier concentration has been significantly reduced.
Abstract: Well characterized Ln1−xCaxMnO3 manganites (Ln=La, Pr, Nd, Sm) with x=1/2 and x=1/3 have been investigated by magnetization measurements in pulsed magnetic fields up to 50 T. Using such high fields all the CO phase boundaries were identified in the temperature range 4–300 K. The transition fields at 4.2 K have been determined in a series of polycrystalline samples with x=1/2 and different effective bandwidths. They vary from Hc=8 T for La to ≈30 T for Sm. In this article we have focused on selected H–T phase diagrams. In particular, the results on Pr1/2Ca1/2MnO3, with the ideal 1:1 electron/hole ratio, are compared with Pr2/3Ca1/3MnO3 where the carrier concentration has been significantly reduced. The observed anomalies in the Hc(T) curves are discussed in the light on neutron diffraction data.
6 citations