Mireille Richard-Plouet

Influence of the sol-gel synthesis on the formation of spinel MgAl2O4

Spinel precursors have been obtained by sol-gel processing using either magnesium nitrate and chemically modified aluminum alkoxide or a double alkoxide as raw materials. The xerogels have been characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). It is proposed that the size of the particles is related to the functionality of the aluminum alkoxide. The use of the double alkoxide allowed pure spinel nanosized materials to be obtained.

Structure and magnetic properties of Co+-implanted silica

Abstract Cobalt has been implanted at 30 and 160 keV in three different silica-based substrates. TEM observations and magnetization measurements performed at RT and 5 K show that, after implantation, cobalt is present both as metal particles, few nanometers in size and as smaller oxide particles. Optical absorption measurements show that the presence of oxide particles is linked to the formation of Si–Si bonds during implantation. After thermal treatment under hydrogen, cobalt is entirely in the metallic form and saturation magnetization becomes close to its theoretical value. Last, the initial amount of oxide depends on the OH− content of the substrate.

Irradiations of implanted cobalt nanoparticles in silica layers

Abstract Cobalt ions have been implanted at an energy of 160 keV at fluences of 2×10 16 , 5×10 16 and 10 17 Co + xa0cm −2 in silica layers and at temperatures of 77, 295 and 873 K. The nanocomposites formed have further been irradiated with electrons and swift heavy ions. Magnetic properties of the nanoparticles studied by a SQUID magnetometer at 295 and 5 K have been related to the modification of particle size and size distribution, which have been observed by transmission electron microscopy.

Synthetic transition metal phyllosilicates and organic-inorganic related phases

We present a brief overview of the first-row transition metal phyllosilicates and their organically functionalised analogues obtained under autogenous pressure conditions. Some structural features of phyllosilicates are first recalled and the magnetic properties of Co2+ and Ni2+ phyllosilicates are described. In the second part, the state-of-the-art in organically functionalised phyllosilicates is reported, including our contributions on the structural and magnetic characterisation. The impetus is to enhance the potential of these new compounds as multi-property materials. Since our interest lies in low-dimensional magnetic properties, divalent transition metal cations are involved in the layered inorganic layers, whereas 3-aminopropyltriethoxysilane is used as the silicon source.

Nickel nano-particles in silica gel monoliths: control of the size and magnetic properties

Abstract Monolithic samples containing 1 and 5 mol% of nickel(II) have been prepared. After thermal treatment Ni(II) is reduced to metallic Ni particles, the size of the particles and the inter-particles distances have been controlled by the nickel content and treatment temperatures. The magnetic susceptibility exhibits a maximum (corresponding to blocking temperature TB) below the bifurcation point in the ZFC/FC data, consistent with the description of super-paramagnetism. The maximum shifts toward higher temperature with increasing Ni concentration. In the super-paramagnetic state (T>TB), the low field susceptibility does not follow a Curie–Weiss law. These phenomena could result to inter-particles dipolar interactions.

Magnetic structure and properties of Cu3(OH)4SO4 made of triple chains of spins s=1/2

Cu3(OH)4SO4, obtained by hydrothermal synthesis from copper sulfate and soda in aqueous medium, is isostructural with the corresponding antlerite mineral, orthorhombic, space group Pnma (62), with a=8.289(1) b=6.079(1) and c=12.057(1) A ˚ , V=607.5(2) A ˚ 3 , Z=4. Its crystalline structure has been refined from X-ray single crystal and powder neutron diffraction data at room temperature. It consists of copper (II) triple chains, running in the b-axis direction and connected to each other by sulfate groups. The magnetic structure, solved from powder neutron diffraction data at 1.4 K below the transition at 5 K evidenced by susceptibility and specific measurements, reveals that, inside a triple chain, the magnetic moments of the copper ions (mB=0.88(5) at 1.4 K) belonging to outer chains are oriented along the c-axis of the nuclear cell, with ferromagnetic order inside a chain and antiferromagnetic order between the two outer chains. No long-range magnetic order is obtained along the central chain with an idle spin behavior. r 2002 Elsevier Science (USA). All rights reserved.

Evidence of Eu3+O2− associates by luminescence study of some silicates and aluminosilicates

Abstract Unusual luminescence spectra with a strong 5D0 arr 7F0 line, a high position of the 5D0 level and the occurrence of two lines close to 16550 cm−1, i.e. in a frequency domain at the border between 5D0 → 7F2 and 5D0 → 7F1 transitions, have been evidenced in the case of cordierite, Mg2Al4Si5O18:Eu, mullite, 2Al2O3.SiO2:Eu and lanthanum disilicate, La2Si2 O7:Eu. By comparison with results on apatites and some fluorides, these unusual spectra have been attributed to the presence of a strong and anisotropic crystal field due to an Euue5f8O bonding.

On the nature of metallic nanoparticles obtained from molecular Co3Ru–carbonyl clusters in mesoporous silica matrices

We report on the impregnation of THF solutions of the low-valent heterometallic cluster NEt(4)[Co(3)Ru(CO)(12)] into two mesoporous silica matrices, amorphous xerogels and ordered MCM-41, and a study of its thermal decomposition into metallic nanoparticles by X-ray diffraction, transmission electron microscopy and in situ magnetic measurements under controlled atmospheres. The decomposition of the cluster was monitored as a function of temperature by examining the chemical composition of the particles, their size distributions and their structures as well as their magnetic properties. Treatment under inert atmosphere (i.e. argon) at temperatures below 200 degrees C resulted in the formation of segregated spherical particles of hcp-ruthenium (2.3 +/- 1.0 nm) and hcp-cobalt (3.1 +/- 0.9 nm). The latter is transformed to fcc-cobalt (3.2 +/- 1.0 nm) above 270 degrees C. At higher temperatures, Co-Ru alloying takes place and the Ru content of the particles increases with increasing temperature to reach the nominal composition of the molecular precursor, Co(3)Ru. The particles are more evenly distributed in the MCM-41 framework compared to the disordered xerogel and also show a narrower size distribution. Owing to the different magnetic anisotropy of hcp- and fcc-cobalt, which results in different blocking temperatures, we were able to clearly identify the products formed at the early stages of the thermal decomposition procedure.

Nuclear and magnetic structures and magnetic properties of synthetic brochantite, Cu4(OH)6SO4

Cu4(OH)6SO4 (1) and Cu4(OD)6SO4 (2) were obtained by hydrothermal syntheses from copper sulfate and sodium hydroxide in H2O and D2O, respectively. They crystallize in the monoclinic system, space group P2(1)/a (14), a = 13.1206(5), b = 9.8551(3), c = 6.0295(2) Angstroms, beta = 103.432(3) degrees, V = 758.3(1) Angstroms(3), Z = 4 and a = 13.1187(5), b = 9.8552(3), c = 6.0293(2) Angstroms, beta = 103.410(3) degrees, V = 758.3(1) Angstroms(3), Z = 4, respectively. They are iso-structural to the mineral brochantite and consist of double chains of edge-sharing copper octahedra that are connected to one another by corners to form corrugated planes along bc; these planes are in-turn bridged by the unprecedented mu7-sulfate tetrahedra to give a 3D-structure. All the hydrogen atoms were precisely located from refinement of the neutron powder diffraction data of the deuterated sample. Magnetic susceptibility data reveal a low-dimensional behavior at high temperature and the presence of both ferromagnetic and antiferromagnetic super-exchanges resulting in a 3D long-range antiferromagnetic ordering at 7.5 K accompanied by a small canting of the moments. The transition is confirmed by a lambda-peak in the specific heat. The magnetic structure at 1.4 K shows the moments are oriented perpendicular to the corrugated planes with alternation along +/-a for neighboring chains within the double chains. The enhanced incoherent scattering at low-angle suggests the existence of short-range ferromagnetic clusters.

Synthesis, structure and magnetic properties of copper hydroxysulfates

Abstract Cu 3 (OH) 4 SO 4 and Cu 4 (OH) 6 SO 4 , synthetic equivalent of antlerite and brochantite minerals, have been obtained by hydrothermal synthesis from copper sulfate, soda and H 2 O or D 2 O. Their structures have been refined from single crystal X-ray and/or powder neutron diffraction data. They consists of edge-shared copper octahedron infinite chains connected to each other to define either triple chains in the case of antlerite or corrugated planes in the case of brochantite. Sulfate groups connect the former copper entities. From magnetic susceptibility measurements, both samples reveal a transition towards a 3D antiferromagnetic long range order at low temperature. In the paramagnetic domain, AF interactions are predominant for brochantite whereas ferromagnetic ones are evidenced for antlerite. The magnetic structures have been determined from powder neutron diffraction data and reveal the presence of ferromagnetic chains AF coupled. The magnetic results have been related to the Cu-O-Cu bridge angle values.