Transformations of the quasi-crystalline icosahedral phases formed in the melt-spun AlMn(Si) alloys Al90Mn10, Al86Mn14 and Al75Mn20Si5 have been studied at high temperatures (300-1000 K) by combined measurements of resistivity, differential scanning calorimetry and X-ray diffraction. In Al86Mn14 a direct crystallisation of both the icosahedral phase and the intergranular AlMn solid solution into o-Al6Mn is observed. It is preceded by a 'relaxation' phenomenon, as seen by the DSC curve. The amplitude and temperature dependence of resistivity are well understood by taking into account the different phase contributions to resistivity during the transformation. The same analysis accounts for the measurements of the Al90Mn10 sample. The crystallisation of Al75Mn20Si5 into beta -Al9Mn3Si is more complex and involves several intermediate crystalline phases, in particular the alpha -Al12Mn3Si. Finally, the better stability of the icosahedral phase in Al75Mn20Si5 ( approximately 700 K) compared with AlMn samples ( approximately 600 K) suggests possible structural and electronic differences between the two icosahedral phases.

2014 Les propriétés physiques, température de transition supraconductrice, susceptibilité magnétique, résistivité électrique et pouvoir thermoélectrique de poudres frittées de SmBa2Cu3O7-x, ont été étudiées en fonction des conditions de préparation et donc de la stoéchiométrie en oxygène.Le champ critique Bc2 a été estimé à partir de mesures de résistivité en champ maximum de 8 T et la pente (dBc2/dT)Tc a été trouvée voisine de 4 T K-1 dans les échantillons à plus haut Tc.Une étude de la résistivité sous pression hydrostatique (0-18 kbar) montre que Tc augmente avec la pression (dTc/dp = 0,5 K kbar-1).Enfin des mesures de caractéristique courant-tension indiquent que des jonctions de type Josephson ou de type S-I-N (Supraconducteur-isolant-métal normal) existent à l'intérieur des échantillons, par suite de l'inhomogénéité de composition.Abstract.-Sintered powders of SmBa2Cu3O7-x have been prepared and characterized.The physical properties, superconducting temperature transition, up to 92 K, magnetic susceptibility, electrical resistivity and thermopower have been studied as a function of the preparation conditions and therefore of oxygen stoichiometry.The upper critical field has been estimated from resistivity measurements in fields up to 8 T and the slope (dBc2/dT)Tc found to be close to 4 TK-1 for the highest Tc samples.Studies of the electrical resistivity under hydrostatic pressures up to 18 kbar show an increase of Tc under pressure with dTc/dp ~ 0.5 K kbar-1.Finally measurements of voltage-current characteristics indicate that either Josephson junctions or superconductor-insulator-normal metal junctions can be found inside the samples, as expected in inhomogeneous materials.

Powders of Yb-Ba-Cu-O, Tm-Ba-Cu-O and Sm-Ba-Cu-O have been synthetized. Electrical resistivity and magnetic susceptibility measurements show that they are superconducting with onset transition temperatures in the range 91 K – 85 K. The thermopower, in these oxides as well as in SrxLa2−xCuO4−δ and Ba2YCu3O7−δ, is found to be positive between Tc and 300 K. Hysteresis of the diamagnetic magnetization is also reported.

Ion mixing of FeNi-Si multilayers is performed at the same dose of 3.1015 Xe+ cm−2 with either of the three energies 200, 300 or 400 keV. The irradiation is done at liquid nitrogen temperature (LNT) or at room temperature (RT). The mixed layers are characterized by reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM), Rutherford backscattering (RBS), secondary ion mass spectroscopy (SIMS) and ferromagnetic resonance (FMR). Films made at 400 keV are more reproducible and as homogeneous as the best amorphous films realized up to now, using sputtering techniques.

2014 The electrical and magnetic properties between 2 K and 300 K, the low temperature specific heat and the crystal structure at 300 K have been studied on single crystals of K0.9Mo6O17 grown by the electrolytic reduction technique. K0.9Mo6O17 is found to be a quasi two-dimensional metal; this is consistent with the structural data. The transition which takes place below 120 K is due to the partial opening of a gap at the Fermi surface, possibly related to the onset of a charge density wave. J. Physique LETTRES 43 (1982) L-59 L-65 15 JANVIER 1982, Classification Physics Abstracts 72.15E 61.60 65.40E

The titanium and vanadium suboxides MOx (where 1.5 < x < 2 and M is Ti or V) are particularly interesting compounds because many show metal-insulator transitions which result in interesting electrical, magnetic and spectroscopic phenomena. We have grown high purity crystals of the congruently melting compounds Ti2O3, Ti3O5 and V2O3 and mixed compounds using the tri-arc melting technique. Crystals were grown at speeds of 1-1.5 cm/h. The Magneli phases MnO2n-1 (n⩾4) do not melt congruently and therefore we have grown a number of these compounds using chemical vapor transport with TeC14 or NH4C1. Twinned needles typically larger than 1 cm long are grown by pulling transport in 3–5 days. The crystals have been characterized by X-ray diffraction, atomic absorption and gamma-ray activation analysis. In addition, the use of a scanning microcalorimeter made it possible to determine phase transitions on needles weighing as little as 2–10 mg. The stoichiometry was determined using X-ray diffraction, pycnometric density measurements and thermogravimetry.

Annealing shows very different behaviour for Te crystallites in an amorphous GexTe1−x matrix as a function of x (x = 0.1 … 0.5). For x ⩽ 0.2, annealing at increasing temperatures increases the number (size) of the Te crystallites with subsequent GeTe + Te crystallization. However for x ⩾ 0.3 there is first a disappearance of Te crystallites, then an appearance of GeTe crystallites, and subsequently GeTe + Te crystallization. Crystallites of either Te or GeTe act as extrinsic defects which add to the intrinsic ones. Activatioon energy decreases (increases) and conductance increases (decreases) as the number of defects increases (decreases). In all cases the final metallic state is obtained only when both GeTe and Te crystallites are present.

Magnetic properties of multilayer FeNi and Co films with PdCo alloy as intermediate layer are studied versus temperature in a range covering the Curie temperature of the PdCo alloy.

AbstractA study is made of the structural and magnetic properties of (111) films of permalloy (80% Ni, 20% Fe), produced epitaxially (111) Ag on mica. The orientation of the NiFe is parallel to that of the Ag. The anisotropy field is about 2 Oe, and the coercive force is slightly less than this value. The dispersion, α90, is of the order of a degree. The films are largely uniaxial, with a superimposed triaxial component. The presence of a triaxial component is demonstrated by the slow switching properties of the permalloy films, and by their domain structures. It seems that the reversal process, away from the easy axis, is a partial rotation.

AbstractA study is made of the domain‐wall structure of coupled uniaxial ferromagnetic films separated by a thin non‐magnetic layer. It is found that the walls in the two films are not always superimposed. After demagnetization in the hard direction they are separated but tend to cross frequently. After demagnetization in the easy direction, they may be separated and parallel or they may be superimposed. An explanation of this behaviour in terms of wall‐hyphen;quasi‐wall interactions is considered.