138 research outputs found
Interface effects and elastic constants of Ag/Ni superlattices studied by Brillouin scattering
No full textThermomechanical Behaviour of AgNi Multilayers and Magnetoelastic Effects
No full textABSTRACTThe elastic and anelastic properties of AgNi multilayers prepared by sputtering were investigated during the course of anneal cycles. The respective temperature variations of some of the elastic constants and moduli were followed by Brillouin scattering and dynamical methods based on use of a torsion pendulum and a vibrating-reed system. The last two enabled to investigate the internal damping associated with the presence of two-dimensional defects. It appears that the motion of interfaces and grain boundaries is inhibited by the high defect density. In contrast, substantial effects associated with the motion of the magnetic domain walls were evidenced. Concurrently, internal stresses were studied by in situ deflection measurements. Flow stress values on the order of 1 GPa were observed. Dilatometry experiments showed that a large part of the non-recoverable modifications in the state of stress induced by thermal cycling originates in the densification of the material.</jats:p
Selective determination of the C11 elastic constant in unsupported Ag/Ni superlattices by Brillouin scattering
No full textThe first selective determination of the effective elastic constant c11 in thick, unsupported metallic superlattice samples has been achieved using Brillouin light scattering. This enabled Young's modulus to be estimated. Measurements of the macroscopic Young's modulus were also performed on identical samples using a tensil micromachine. The two approaches, surface phonons and static elasticity, give results mutually consistent in the Ag/Ni superlattices studied. In addition, no significant dependence on period was found in either case. © 1992
Pinned synthetic ferrimagnets with perpendicular anisotropy and tuneable exchange bias
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Pinned synthetic ferrimagnets (syFerri) with perpendicular-to-plane magnetic anisotropy, of the form AP1/Ru/AP2/FeMn [where AP1 and AP2 are (Co/Pt) multilayers], have been prepared and characterized. The magnitudes of the exchange bias fields of both AP1 and AP2 can be tuned at room temperature by simply varying the relative number of (Co/Pt) repeats in each multilayer. This effect can be quantitatively interpreted by considering the different energy contributions involved during magnetization reversal. Moreover, from the values of these fields, the characteristic parameters of the system (i.e., coupling strength through the Ru and AP2/FeMn pinning energy), can be evaluated. Interestingly, an extended plateau with a virtually constant magnetization is observed around zero field when the number of Co/Pt repeats in AP1 is equal or larger than in AP2. This is very appealing for field sensor or memories applications using spin valves or tunnel junctions with perpendicular anisotropy, since it offers a large dynamic range over which the magnetic configuration of the syFerri remains stable
Proceedings of the Joint European Magnetic Symposia JEMS'01 ; 28 August - 1 September 2001, Grenoble, France
No full textTHE MEDIUM RANGE STRUCTURE OF HYDROGENATED Cu-Ti AMORPHOUS ALLOYS STUDIED BY ANOMALOUS SMALL-ANGLE SCATTERING OF X-RAYS AND NEUTRON DIFFRACTION
No full textLes alliages amorphes Cu-Ti donnent une forte diffusion centrale après hydrogénation. Celle-ci est analysée par diffusion anomale des rayons X sur les seuils K du cuivre et du titane. On peut alors conclure à la présence de très petits agrégats d'hydrure de titane de composition TiH2. Ces résultats sont en accord avec ceux obtenus par diffraction des neutrons en utilisant soit l'hydrogène (b 0) pour l'hydrogénation des échantillons.Amorphous Cu-Ti alloys, when hydrogenated, reveal a strong small-angle scattered intensity. The anomalous X-ray scattering effect is used to analyse this SAS intensity on both copper and titanium edges. It allows to assert the presence of very small clusters of titanium hydride having the TiH2 composition. These results are in good agreement with those obtained by neutron scattering experiments when using either hydrogen (b 0) for the hydrogenation of the samples
Size effects on exchange bias in sub-100 nm ferromagnetic-antiferromagnetic dots deposited on prepatterned substrates
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Exchange bias effects have been investigated in ferromagnetic (FM)-antiferromagnetic (AFM) square dots, with lateral sizes of 90 nm, sputtered on a prepatterned Si substrate. The magnetic behavior of the dots has been compared with that of a continuous FM-AFM bilayer with the same composition. Along the unidirectional direction, the dots exhibit square hysteresis loops and preserve an exchange bias field, HE, of 70 Oe at room temperature, which is about 40% smaller than HE in the continuous film. In addition, the distribution of blocking temperatures in the nanostructures is found to be shifted toward lower values with respect to that in the continuous film. These results can be interpreted assuming that the reduced lateral dimensions of the nanostructures impose some constraints on the formation and pinning of domain walls in the AFM layer
Mössbauer investigations of Nafion membranes
No full textMössbauer experiments have been performed on Nafion ion exchange membranes neutralized with iron chloride. The recoilless fraction falls to zero at a temperature which depends on the water content, showing that the rigidity of the local ion environment is greatly influenced by the amount of water retained in these membranes. Two different iron sites are defined, whose relative intensities vary with water content. One of the doublets is attributed to a (Fe2+, H 2O complex whose hyperfine parameters are essentially independent of the quantity of water. The second doublet is attributed to a less hydrated species. No evidence of magnetic hyperfine structure is found, even at 4.2 K.Des expériences d'effet Mössbauer ont été réalisées sur des membranes Nafion neutralisées avec du chlorure de Fer. Le facteur f s'annule à une température qui dépend de la teneur en eau, ce qui montre que la rigidité de l'environnement local de l'ion est fortement influencée par la présence d'eau à l'intérieur de ces membranes. I1 est possible de définir deux sites différents de Fer dont les proportions relatives varient avec la concentration en eau. L'un des deux doublets est attribué à un complexe (Fe2+, H 2O dont les paramètres hyperfins sont à peu près indépendants de la teneur en eau. Le deuxième doublet est attribué à un ion moins hydraté. Les spectres ne révèlent pas la présence d'une structure magnétique hyperfine, même à 4,2 K
- …
