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| 2. |
- Ahlberg, Martina, et al.
(författare)
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Influence of boundaries on magnetic ordering in Fe/V superlattices
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:21, s. 214429-
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Tidskriftsartikel (refereegranskat)abstract
- We study the role of surface boundaries on the magnetic properties of [Fe/V](n) superlattice structures, with n=2-10. Using the magneto-optical Kerr effect and polarized neutron reflectivity measurements, we examine the evolution of both the total and the layer-resolved magnetizations as a function of temperature. By varying n, we observe a large shift in the transition temperatures T-c and a substantial change in the total magnetization critical exponent beta. In particular, the thicker samples exhibit nonuniversal exponent values. By resolving the magnetization as a function of position within the superlattice, we show that this behavior arises from contributions of the surfaces. Furthermore, we attribute the large shift in T-c to long-ranged interactions present in the superlattice.
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| 3. |
- Björck, Matts, et al.
(författare)
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The effect of strain and interfaces on the orbital moment in Fe/V superlattices
- 2007
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 313:1, s. 230-235
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the Fe orbital moment on strain and interfaces in Fe/V superlattices has been investigated by X-ray magnetic circular dichroism (XMCD). The orbital moment was determined to be lower at the interfaces than in the bulk, which we attribute to Fe–V hybridization. An enhancement of the orbital moment with increasing strain in the Fe layers was observed. This enhancement is attributed to an unquenching of the orbital moment. Consequently, the orbital moment of Fe in Fe/V is concluded to be influenced by two competing parameters. It is lowered by increasing interface density, and enhanced by increasing strain.
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| 4. |
- Granroth, Sari, et al.
(författare)
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Investigation of interface properties of Ni/Cu multilayers by high kinetic energy photoelectron spectroscopy
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 80:9
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Tidskriftsartikel (refereegranskat)abstract
- High kinetic-energy photoelectron spectroscopy (HIKE) or hard x-ray photoelectron spectroscopy has been used to investigate the alloying of Ni/Cu (100) multilayers. Relative intensities of the corelevels and their chemical shifts derived from binding energy changes are shown to give precise information on physicochemical properties and quality of the buried layers. Interface roughening, including kinetic properties such as the rate of alloying, and temperature effects on the processes can be analyzed quantitatively. Using HIKE, we have been able to precisely follow the deterioration of the multilayer structure at the atomic scale and observe the diffusion of the capping layer into the multilayer structure which in turn is found to lead to a segregation in the ternary system. This is of great importance for future research on multilayered systems of this kind. Our experimental data are supplemented by first-principles theoretical calculations of the core-level shifts for a ternary alloy to allow for modeling of the influence of capping materials on the chemical shifts.
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| 5. |
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| 6. |
- Kvashnina, Kristina, et al.
(författare)
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Changes in electronic structure of copper films in aqueous solutions
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:22, s. 226002-
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Tidskriftsartikel (refereegranskat)abstract
- The possibilities for using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the Cu oxidation state and changes in the electronic structure during interaction between copper and ground-water solutions were examined. Surface modifications induced by chemical reactions of oxidized 100 Å Cu films with Cl−, SO42− and HCO3− ions in aqueous solutions with various concentrations were studied in situ using liquid cells. Copper corrosion processes in ground water were monitored for up to nine days. By comparing Cu 2p–3d, 4s transitions for a number of reference substances previously measured, changes in electronic structure of the Cu films were analysed. The XAS and RIXS spectral shape at the Cu edge, the chemical shift of the main line for Cu2+, and the energy positions of the observed satellites served as a tool for monitoring the changes during the reaction. It was found that the pH value and the Cl− concentration in solutions strongly affect the speed of the corrosion reaction.
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| 7. |
- Kvashnina, Kristina O., et al.
(författare)
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In situ X-ray absorption study of copper films in ground water solutions
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 447:1-3, s. 54-57
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Tidskriftsartikel (refereegranskat)abstract
- This study illustrates how the damage from copper corrosion can be reduced by modifying the chemistry of the copper surface environment. The surface modification of oxidized copper films induced by chemical reaction with Cl− and in aqueous solutions was monitored by in situ X-ray absorption spectroscopy. The results show that corrosion of copper can be significantly reduced by adding even a small amount of sodium bicarbonate. The studied copper films corroded quickly in chloride solutions, whereas the same solution containing 1.1 mM prevented or slowed down the corrosion processes.
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| 8. |
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| 9. |
- Marcellini, Moreno, 1976-
(författare)
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Magnetic Ordering in Layered Magnets
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The preparation of layered magnets needs the knowledge of growth techniques which are focused on the growth of Fe/V(001) superlattices. Such films have been structurally investigated by X-rays reflectivity and diffraction. The magnetic investigations have been carried out by magneto-optic Kerr effect (MOKE), Superconducting Quantum Interference Device (SQUID) magnetometry and polarized neutron reflectivity (PNR). This latter technique has been used in cooperation with the Institute Laue Langvin (Grenoble, France) and Ruhr Universität (Bochum, Germany). The cross-over in universality class is shown in a series of layered magnets where a δ-doping layer of Fe has been embedded between two layers of Pd showing that the magnetization depends on the effective magnetic thickness of the polarized Pd. A model for the cross-over has been developed in terms of magnetic excitations. The interlayer exchange coupling (IEC) mediated by a non-magnetic spacer has been reviewed focusing the attention on the recent theoretical and experimental works based on Fe/V(001) superlattices. The IEC can be tailored at will by reversibly alloying of the spacer with H: this has been proved in Fe/V(001) double layers showing that in the two dimensional limit, the universality class is not affected by the coupling. The magnetic order-disorder transitions in Fe/V(001) superlattices do not seem to belong to any universality class. A phenomenological model which accounts for the effective coupling at the boundaries has been developed. The influence of the inherent ordering temperatures of single magnetic layers has been investigated in Fe/V(001) superlattices proving that the weakest ferromagnetic layer affects the overall magnetic ordering. A new kind of layered magnet has been developed to increase the effect of the boundaries. PNR measurements show that the universality class depends on which length-scale is investigated.
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| 10. |
- Marcellini, Moreno, et al.
(författare)
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The influence of interlayer exchange coupling on the magnetic ordering in Fe/V superlattices
- 2009
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 321:9, s. 1214-1220
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Tidskriftsartikel (refereegranskat)abstract
- The relation between the interlayer exchange coupling and magnetic order is addressed, using Fe/V(0 0 1) superlattices as a model system. Large decrease in the ordering temperature (Tc) is observed with decreasing interlayer exchange coupling. The effective exponents of the magnetization were determined to be larger than 0.5 for all the samples, which is strongly deviating from the classical values of both two- and three-dimensional systems. This effect can partially be ascribed to the presence of boundaries, invoked by the finite number of magnetic layers.
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