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11.
G. Alvarez H. Montiel D. de Cos A. García-Arribas R. Zamorano J.M. Barandiarán R. Valenzuela 《Journal of Non》2008,354(47-51):5195-5197
Microwave absorption measurements on a NiFe/Au/NiFe multilayer film were carried out at X-band (8.8–9.8 GHz). The angular dependence of microwave absorption, both in ferromagnetic resonance (FMR) and low-field microwave absorption (LFA), is investigated in two orientations. In both cases the film plane is orientated parallel to the AC field. In the longitudinal orientation, the film axis makes angles between 0° and 90° with the DC magnetic field (Hdc). In the transverse orientation, the film axis is always perpendicular to Hdc, marking angles between 0° to 90° with the axis of the induced transverse anisotropy. For the longitudinal orientation, FMR spectra suggested a compound absorption mode that can be interpreted as the combination of two different magnetic phases. Additionally, these measurements showed an increase in the resonance field as a function of the angle, which can be explained in terms of a contribution of shape anisotropy field (SAF). For this same orientation, the LFA spectra exhibited a compound antisymmetric shape around zero field with double peaks, which we associated with each one of the magnetic phases. The separation of these peaks increased as a function of the angle between the DC field and the multilayer film axis, suggesting also a contribution from SAF. In the transverse orientation, we observed an additional contribution of induced transverse anisotropy field (ITAF) in FMR measurements. The LFA measurements exhibited differences with the longitudinal orientation which are also associated with ITAF. 相似文献
12.
Non-isothermal equations describing the liquid-crystal transformation are derived using the isothermal Avrami equations. A theoretical expression for the critical cooling rate for the formation of a glass is found. Calculations based on this expression are in better agreement with experimental values than those derived from TTT (time-temperature-transformation) curves. A study performed on typical glass forming materials enables the glass forming ability (GFA) to be determined by experimentally measuring crystallization temperatures at different cooling rates which are easily accessible with commonly available technology. The behaviour of the rate constant for crystallization is also obtained from the same data in the experimental range considered. In both cases no previous knowledge of the parameters involved is needed.With some assumptions the values of the viscosity in the crystallization temperature range can be estimated.Although the study was performed for an Avrami index of 4 an extension to other values of n is made under some restricted conditions and a more general treatment is outlined. 相似文献
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Diverging pathways to topologically complex polycyclic bis-acetals and their ring system interchange
Castillo RR Aquino M Gandara Z Safir I Elkhayat Z Retailleau P Arseniyadis S 《Organic letters》2012,14(6):1628-1631
Carbinol-tethered octalin-diols (1), which differ only by the C11 configuration at the angular position, were transformed selectively to three types of structurally unrelated original scaffolds such as unsymmetrical octahydroanthracenes (5/7), furofuranes (6), or spirans (8/9) via a two-step protocol. The 11S* configuration ensures a C13-C4 Friedel-Crafts type C-C bonding (through an unprecedented oxidative cleavage-triggered domino process) while the 11R* configuration allows for a C13-C2 Marson-type Friedel-Crafts C-C bonding (through a nucleophilic acetal opening). 相似文献
15.
Pilar Puebla Zoila Honores Manuel Medarde Esther Caballero Arturo San Feliciano Lourdes Morn 《Journal of heterocyclic chemistry》1999,36(4):1097-1099
Enaminones are widely employed in the synthesis of heterocycles, however heterocyclic enaminones and their use in the synthesis of more complex systems have been less studied. The reaction between 4-chloroacetylacetate and aliphatic or aromatic 1,2-aminoalcohols, 1,2-aminothiols or 1,2-diamines, yields in one pot a six-membered 1,4-heterocyclic system containing the enaminone moiety. 相似文献
16.
T. HernÁndez F. Plazaola J. M. Barandiarán J. M. Greneche 《Hyperfine Interactions》2005,161(1-4):113-122
We have synthesized by sol–gel method the following polycrystalline double perovskite samples: Sr2Fe1?x Sc x ReO6 (x = 0, 0.05, 0.1). The results of the Rietveld refinements presented single double perovskite phases with orthorhombic symmetry for the system Sr2Fe1?x Sc x ReO6, the differences in atomic radii between Fe3+ and Sc3+ cause a lowering in symmetry with respect to the parent Sr2FeReO6 tetragonal compound. The Curie temperatures are found at about 426 and 436 (±5) K for Sr2Fe0.9Sc0.1ReO6 and Sr2Fe0.9Sc0.05ReO6, respectively. The Mössbauer spectra measured at 77 K show complex hyperfine structures resulting from different magnetic contributions at Fe3+ sites; the average hyperfine field is estimated 50 T and the isomer shift at 0.5 mm/s. At room temperature an intermediate valence state for Fe is also observed. 相似文献
17.
J. M. Barandiarán J. J. Del Val J. Colmenero C. Lacabanne D. Chatain J. Millán 《Journal of Macromolecular Science: Physics》2013,52(5-6):645-663
Thermally stimulated currents (TSC) have been measured in several samples of poly(vinyl chloride) differing in tacticity and molecular weight as a result of polymerizing them at different temperatures. This has allowed us to characterize the relaxation behavior of PVC. No dielectric relaxation can be observed by this experimental technique at temperatures between liquid helium and liquid nitrogen. The β relaxation is observed around 173°K, with similar parameters in all samples studied. Around the glass transition the relaxation times isolated in the α peak follow a compensation law. Molecular weight and tacticity have a strong influence on the temperature of the maximum and the intensity of this relaxation, respectively. 相似文献
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P. Lázpita J. M. Barandiarán J. Gutiérrez M. Richard S. M. Allen R. C. O'Handley 《The European physical journal. Special topics》2008,158(1):149-154
Structural and magnetic transition temperatures of
ferromagnetic shape memory alloys present a strong dependence on
slight departures from the stoichiometry, as does the mobility of
twin boundaries responsible for the large magnetic field induced
strains. In this work we study four non stoichiometric Ni-Mn-Ga
polycrystalline alloys with compositions of 43–52 at.% nickel,
excess manganese and deficient in gallium, and a single crystal of
composition Ni52Mn26Ga22. Those compounds are of
technical interest due to the observed large room temperature
magnetic field induced strains. Calorimetric and magnetic
measurements determined the martensitic transition and Curie
temperatures of the alloys (AS = 331 K and
TCurie = 366 K for 52 at.% nickel alloy).
Nickel defective alloys present a martensitic transition region
broader than excess nickel ones. Neutron powder diffraction analysis
confirmed orthorhombic martensitic structures for nickel defective
alloys, and tetragonal for excess nickel ones. In the 52 atomic %
nickel alloys case the crystallographic structure of the martensitic
phase was also obtained on a single crystal with the same
composition, trained to get a single variant in agreement with
determined in the powder sample. 相似文献
20.
Pérez-Landazábal JI Recarte V Sánchez-Alarcos V Chernenko VA Barandiarán JM Lázpita P Rodriguez Fernández J Righi L 《J Phys Condens Matter》2012,24(27):276004
The magnetic, magnetocaloric and thermal characteristics have been studied in a Ni(50.3)Mn(20.8)Ga(27.6)V(1.3) ferromagnetic shape memory alloy (FSMA) transforming martensitically at around 40?K. The alloy shows first a transformation from austenite to an intermediate phase and then a partial transformation to an orthorhombic martensite, all the phases being ferromagnetically ordered. The thermomagnetization dependences enabled observation of the magnetocaloric effect in the vicinity of the martensitic transformation (MT). The Debye temperature and the density of states at the Fermi level are equal to θ(D)?=?(276?±?4)?K and 1.3?states/atom?eV , respectively, and scarcely dependent on the magnetic field. The MT exhibited by Ni-Mn-Ga FSMAs at very low temperatures is distinctive in the sense that it is accompanied by a hardly detectable entropy change as a sign of a small driving force. The enhanced stability of the cubic phase and the low driving force of the MT stem from the reduced density of states near the Fermi level. 相似文献