Showing papers by "Marc Respaud published in 2000"
TL;DR: In this article, the reaction of Co(η3-C8H13) and Pt2(dba)3 (dba = bis-dibenzylidene acetone) under dihydrogen leads in the presence of poly(vinylpyrrolidone) to nanometric bimetallic particles CoxPt1-x.
Abstract: The reaction of Co(η3-C8H13)(η4-C8H12) and Pt2(dba)3 (dba = bis-dibenzylidene acetone) under dihydrogen leads in the presence of poly(vinylpyrrolidone) to nanometric bimetallic particles CoxPt1-x. The composition of the material is determined by the initial ratio of the two organometallic precursors. The bimetallic character of the particles is evidenced by magnetic, structural, and spectroscopic studies. Structural changes are evidenced both by HREM and WAXS: platinum rich particles adopt a fcc crystalline structure while cobalt rich particles adopt a non periodic polytetraedral arrangement. The magnetic properties of the materials have been investigated. ZFC/FC measurements show that the particles are superparamagnetic and that their size dispersity is very low. From isothermal magnetization measurements, the extrapolated value of the coercive field HC(T = 0) is shown to increase continuously with Pt concentration, which is characteristic of bimetallic particles.
122 citations
TL;DR: In this article, the coexistence of ferromagnetic metallic and antiferromagnetic charge-ordered (CO) states was investigated using zero-field muon spin relaxation, neutron diffraction, calorimetric, and magnetic measurements.
Abstract: The coexistence of ferromagnetic metallic and antiferromagnetic charge-ordered (CO) states in ${\mathrm{Pr}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ has been investigated using zero-field muon spin relaxation, neutron diffraction, calorimetric, and magnetic measurements. Calorimetric data evidence a high degree of disorder below the CO transition. The data are consistent with large antiferromagnetic (AFM) CO regions containing structural and magnetic inhomogeneities densely scattered. Below the charge order temperature ${(T}_{\mathrm{CO}}\ensuremath{\approx}220\mathrm{K})$ the dominant relaxation mechanism of the muon polarization is based on ferromagnetic Mn-Mn correlations and the spin-lattice relaxation rate is peaked at ${T}_{C}$ instead of ${T}_{N}.$ The results agree with a spatial distribution of ferromagnetic and AFM regions strongly interpenetrated. The presence of local magnetic order in the whole sample is only achieved just below ${T}_{C}\ensuremath{\approx}120\mathrm{K}.$
30 citations
TL;DR: In this paper, the Shubnikov-de Haas (SdH) effect has been studied in single-crystal samples of the CoSb in pulsed magnetic fields up to 35 T. From the temperature dependence of the amplitude of the SdH oscillations the values of cyclotron effective mass were determined.
Abstract: Shubnikov--de Haas (SdH) effect has been studied in single-crystal samples of $p\ensuremath{-}{\mathrm{CoSb}}_{3}$ in pulsed magnetic fields up to 35 T. From the temperature dependence of the amplitude of the SdH oscillations the values of cyclotron effective mass were determined. It was found that the effective mass increases from ${0.07m}_{0}$ to ${0.15m}_{0}$ with increasing of the hole concentration, taking part in the SdH effect, from 0.46 to $4.06\ifmmode\times\else\texttimes\fi{}{10}^{18}{\mathrm{cm}}^{\ensuremath{-}3},$ indicating a nonparabolicity of the valence band of ${\mathrm{CoSb}}_{3}.$ The fundamental band parameters, the band-edge effective mass ${(m}_{n}^{*}{/m}_{0}=0.049\ifmmode\pm\else\textpm\fi{}0.006),$ energy gap ${(E}_{g}=31\ifmmode\pm\else\textpm\fi{}5\mathrm{meV}),$ spin-orbit splitting $(\ensuremath{\Delta}=0.16\ifmmode\pm\else\textpm\fi{}0.06\mathrm{eV}),$ and the interband momentum matrix element $[P=(2.0\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\mathrm{eV}\mathrm{}\mathrm{cm}]$ were estimated using the three-band Kane model.
25 citations
TL;DR: In this article, the stability of the charge ordering phases of Ln 1/2 Ca 1 2 MnO 3 (Ln=La, Pr, Nd, Sm, Y, and Ho) and Bi 1/4 Ca 3/4 MnO3 was investigated and the magnetisation measurements showed a magnetic-field-induced transition which collapsed the antiferromagnetic or paramagnetic charge ordering phase to a ferromagnetic phase.
6 citations
TL;DR: In this article, it was shown that diffusive magnetic polarons compete with the particular orbital ordering of the Jahn-Teller distorted phase in the temperature interval 0.8
Abstract: Muon relaxation techniques have been used to investigate the spin dynamics and magnetic transitions of the La7/8Sr1/8MnO3 manganite. Competing orbital states cause changes in the ferromagnetic coupling strength and mechanism. The data suggest that diffusive magnetic polarons compete with the particular orbital ordering of the Jahn–Teller distorted phase in the temperature interval 0.8
5 citations
TL;DR: In this article, a comparative study of charge-ordered Mn perovskites with commensurate and incommensurate charge concentration was performed, where the ferromagnetic correlations were the dominant relaxation mechanism.
Abstract: Muon relaxation techniques are used in a comparative study of charge-ordered Mn perovskites with commensurate (Pr 1/2 Ca 1/2 MnO 3 ) and incommensurate (Pr 2/3 Ca 1/3 MnO 3 ) charge concentration. A strong modification of the spin dynamics is observed in Pr 2/3 Ca 1/3 MnO 3 for which the ferromagnetic correlations are the dominant relaxation mechanism.
1 citations