In this study, results are reported on the composition and the electrical and magnetic properties of thin films of nickel deposited by metal-organic CVD (MOCVD) from nickelocene. It was found that the films contain carbon, whose content decreases with increasing deposition pressure and hydrogen flow rate and with decreasing molar fraction of the precursor. Ferromagnetic properties, namely saturation magnetization, Curie temperature, and also electrical conductivity of the films decrease with increasing carbon content. The evolution of the saturation magnetization M-s of the films with measurement temperature follows Bloch's law. Carbon is found in the films in different forms, namely carbidic (interstitial), aliphatic, or cyclic. Deposition of these forms is discussed and is correlated with the variations of the properties of the films.

In this study, results are reported on the composition and the electrical and magnetic properties of thin films of nickel deposited by MOCVD from nickelocene. It was found that films contain carbon, whose content decreases with increasing deposition pressure. Part of the carbon atoms are found in interstitial position in the Ni lattice. Saturation magnetization, Curie temperature and electrical conductivity of the films decrease with increasing their carbon content. The evolution of the magnetization saturation Ms of the films with temperature follows Bloch's law. The different forms, namely carbidic (interstitial),;aliphatic, or cyclic, in which carbon is found are discussed, and are correlated with the variations of the properties of the films.

We report neutron scattering experiments on several Al-Pd-Mn liquid alloys with Mn content between 3.5 and 7.2 at. % which are in thermodynamical equilibrium with icosahedral quasicrystalline or approximant phases. The results reveal an overall similarity between the structure factor in the solid and in the liquid states, suggesting the presence of a strong icosahedral local order in the liquid state. Simulations of the structure factor at large momentum transfer support this interpretation. In addition, a marked increase of the neutron scattering cross section at small momentum transfer occurs on melting, revealing the appearance of paramagnetic scattering in the liquid state. A comparison with susceptibility measurements combined with additional neutron scattering experiments using polarized neutrons, demonstrates that magnetic moments are present in the liquid state and not in the solid state. In the liquid state, at a given temperature, the same spin value can be extracted from the paramagnetic scattering and the susceptibility data. The link between the evolution of the magnetic properties and that of the short- and medium-range order at the melting point is discussed. Surprisingly, the paramagnetism continues to increase with temperature in the liquid state. This remarkable behavior might be due either to an increase of the spin value with temperature as a consequence of thermal expansion or to the coexistence of magnetic and nonmagnetic Mn in temperature-dependent proportions. The origin of this behavior is discussed in relation to the evolution of the liquid structure.

Ni/Cr multilayers have been grown on Si(100) by dc triode sputtering. Three different samples have been investigated where the only purposely variable parameter is the superperiod: Λ = 52, 35 and 27 Å. The Ni:Cr ratio was kept constant equal to 1:1 and the total thickness is about 1200 Å. The quality of the layering is shown by the low-angle X-ray diffraction spectra which exhibit both thickness fringes and Bragg peaks. At large angles, weak superlattice peaks appear around the 110Cr/111Ni diffraction peak. Pole figure measurements indicate a fiber texture: <111> for Ni and <110> for Cr. The average stress in the stackings has been evaluated via curvature measurements: the samples are in a high state of compressive stress, larger than 1 GPa. Systematic magnetization measurements have been performed with a vibrating sample magnetometer as a function of temperature with the applied field parallel or perpendicular to the sample plane. All the multilayers exhibit in-plane anisotropy. The magnitude of the saturation magnetization indicates an important Ni-Cr intermixing at the interfaces. The temperature behaviour of the magnetic moment indicates two-dimensional effects.

Synthesis of compounds belonging to the FeRhP system reveal the existence of three main structures: hexagonal H3-Fe2P type, orthorhombic O10-NdCoB type, and hexagonal H12-FePdP type described as polytypes resulting from different packings of a pseudorhombohedral FeRhP subcell. High magnetic field magnetic measurements were carried out in the 4.2–300 K temperature range in fields up to 200 kOe. Very different magnetic properties were observed for the three phases. To explain the low saturation magnetization of both O10 and H12 phases compared to that of the H3 phase, a structural magnetic framework that leads to the formation of diamagnetic clusters within the ferromagnetic matrix is proposed.

YBa2Cu3O7 films, with thickness ranging between 0.08 and 0.48μm were deposited on SrTiO3 substrates, using a newly developed aerosol MOCVD method. The critical current density of these films was measured in magnetic fields up to 4T in the temperature range from 20 to 77K using magnetization and ac screening techniques.

The magnetization processes of two series of sandwiches of compositions Sm-Co/Co/Sm-Co′ and Sm-Co/Gd-Co/Sm-Co′ prepared by dc bias sputtering are presented. The layers of Sm-Co and Sm-Co′ have different compositions each with a different coercive field. The central layer consists of a soft magnetic material with a thickness varying from 500 to 5000 Å. In these systems, it is possible to stabilize a magnetic configuration with the magnetic moments of the external layers having opposite directions. Due to the magnetic coupling between the layers associated with the strong exchange interactions between cobalt atoms throughout the whole sample, a large planar Bloch wall is formed in the central layer. The width of this wall depends on the intrinsic properties of this central layer, but the magnetization processes vary with the relative magnitude of the wall width to the thickness of this layer. For a large thickness of the central layer, the Bloch wall is very mobile under applied field leading to a very large susceptibility.

A dia-paramagnetic transition comes before melting of the icosahedral phases Mn-Pd-Al. The transition and the increase in stability given by palladium result in the occurrence of diamagnetic clusters. Previously, a similar mechanism has been suggested to take place and allows description of the polytypisme encountered in MM'P and MM'As compounds.

The critical current density (J(c)) for zero magnetic field has been measured as a function of temperature in c-oriented thin layers of YBa2Cu3O7-x prepared by different synthesis methods. One direct and two indirect J(c)(T) methods were employed for each film: transport measurements on patterned film constrictions, DC remanent magnetization studies using the Bean model and non-linear AC screening analysis. Results from the indirect methods were calibrated against transport data. Possible origins of observed dependences are suggested and calibration procedures are discussed. The investigation demonstrated the feasibility of using AC screening analysis in rapid determinations of J(c)(T) close to T(c).

Nd2Fe14BHx micron-size loose particles have been synthetised through the well known oxide reduction-diffusion (ORD) technique. When excess Ca is used as reducing agent, an exothermic reaction is observed by washing under water, with the production of native hydrogen that diffuses in the interstitial sites of the alloy. Depending on the experimental conditions, different contents of hydrogen intercalation have been observed, with x ranging from x approximately 0 to x approximately 4-5. Cell parameters were observed quickly increasing with hydrogen uptake, resulting in a drastic and regular decrease of the coercivity.In order to understand the relation between the coercivity and the content of hydrogen uptake, 2 to 4 mum size powders of a highly coercive Nd2Fe14B industrial alloy have been submitted to a native hydrogen environment obtained through different chemical conditions. A very reliable relationship has been established between the cell parameters (and thus the content or interstitial hydrogen) and the coercivity of the alloy particles. The degradation of the coercivity of industrial magnets submitted to moisture corrosion could well result from the formation of low coercive layers -with a high hydrogen content- at the surface of grains, resulting in the possibility to initiate reverse nucleus domains.

Thin-film growth and compositional effects of c-axis oriented YBa2Cu3O7-x (YBCO) thin films synthesized by metalorganic chemical vapor deposition have been investigated. The formation of single cation films using tetramethylheptanedionate precursors was shown to be mass controlled, exhibiting a ratio of deposited to evaporated species in the increasing order Ba, Y, and Cu. The physical properties of off-stoichiometric YBCO films deposited on MgO substrates were measured in the compositional range 1.1 less-than-or-equal-to Ba/Y less-than-or-equal-to 2.3 and 1.5 less-than-or-equal-to Cu/Ba less-than-or-equal-to 4.6. While structural properties such as c-axis values and rocking curves appeared unaffected to variations in cation stoichiometry, morphology was observed to be extremely sensitive even to slight changes in composition. Off-stoichiometric layers with Cu/Ba > 1. 5 were observed to exhibit Cu-rich precipitates embedded in a 1:2:3 YBCO film matrix. The zero-resistivity temperatures were above 77 K for all cation film compositions measured. However, sharp ac-susceptibility transitions were restricted to a more narrow compositional range (1.9 < Cu/Ba < 3.6). The best superconducting properties [T(c) = 85 K, J(c) (77 K) > 10(6) A/cm2] were observed for films with relatively rough surface morphologies (Ba/Y = 1. 6 and Cu/Ba = 3.5). An optimum trade-off between smooth surfaces and superconducting properties was found for Ba/Y = 1.5 and Cu/Ba = 1.9, yielding T(c) = 81 K and J(C) (77 K) = 3 X 10(5) A/cm2.

Epitaxial thin layers of YBa2Cu3O7−x are synthesised by thermal decomposition (750 – 830 °C) of tetramethylheptanedionates of yttrium, barium and copper in the presence of oxygen. Argon is used as a carrier gas and the partial pressures of the different precursors are monitored via a careful control of the sources temperatures. The superconducting films with thicknesses ranging between 40 nm and 200 nm are grown on (100) SrTiO3, (012) LaA1O3 or (100) MgO. The growth rate varies between 2.7 nm/min and 4 nm/min. The layers are analysed by scanning and transmission electron microscopy, x-ray diffraction and Rutherford backscattering spectrometry. The normal — superconductor transition is investigated via DC and AC resistance, magnetization and AC susceptibility measurements as a function of temperature. Magnetisation hysteresis loops recordings, I–V measurements on microbridges and non linear susceptibility analysis are used to explore the irreversible properties of the layers. Typical parameters for MOCVD films grown on LaA1O3 are as follows: Tc = 90 K, ΔTc = 0.4 K and Jc (77 K) = 2 106 A cm−2.

We report the effect of hydrogen insertion and desorption on technologically formulated Sm2Co17-type compounds that are used for the production of sintered magnets. It is seen that coercivity, which is decreased upon hydrogenation, can be restored and even improved after hydrogen desorption. It has also been shown that this parameter is critically dependent upon the heat treatment. In addition, the effect of transition metal additions on magnetization and coercivity has been studied. Structural and magnetic characterizations have been carried out at each stage of the entire process. The factors that should be taken into consideration for the production of optimized materials are discussed.

Accounting for the d-p type hyhridization with phosphorus, the filling of the d state levels is achieved in the Ni2P-Co2P system with the compound Ni1.2Co0.8P that behaves diamagnetically. The negative contribution to the susceptibility is present apart from this composition and it has been correlated to the formation of diamagnetic clusters whose local ordering has been deduced from neutron diffraction experiments.

M-hexaferrite single crystals of chemical formulae BaFe12-2xIrxO19 with Me = Zn, Co and 0.3 < x < 0.9, were grown from a Bi2O3 flux. Crystal structure refinement studies showed that Ir and Zn cations are exclusively located on octahedral sites in R structural blocks. Saturation magnetizations of these ferrites are consistent with Gorter's spin arrangement, considering there to be a magnetic moment of 5μB on the Ir4+ cations.

For the system (Fe1-xMnx)2P(O<or=x<or=1), numerous previous studies have shown that Fe- and Mn-rich solid solutions crystallise with a hexagonal symmetry (H) and intermediate compositions are of orthorhombic type (O). The H and O phases are those generally encountered in the transition-metal pnictides of formula MM'X(M,M': transition metal; X:P or As). Analysis of the paramagnetic state at the highest temperatures reveals the stability of the H structure for the whole system. The magnetic transition observed at high temperature for intermediate ranges of composition can be related to the crystal O to or from H transformation already observed by neutron diffraction. In most of the cases, a metastable hexagonal phase can be retained by ensuring fast quenching. A complete phase diagram versus composition and temperature, is proposed. The reciprocal paramagnetic susceptibility behaviour as temperature is varied provides evidence for large magnetic correlations far above the ordering temperature for the hexagonal form only. For a given composition, a strong influence of the local metal environment on the magnetic couplings is thus emphasised for both H and O forms of the MM'X series.