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S. Couet,
J. Demeter,
E. Menéndez,
R. Rüffer,
C. J. Kinane,
B. Laenens, A. Teichert,
S. Tripathi,
F. Almeida,
A. Vantomme,
K. Temst
Journal of Applied Physics 01/2013; 113:013909. · 2.17 Impact Factor
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ABSTRACT: Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system
of composition Cu(32nm)/ V(40nm)/Fe(1nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied
and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e., preparing
the V(40nm)/Fe(1nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively. A new
magnetic state of the system was observed at temperatures below 0.7T
C manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature
from 0.7T
C to T
C, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. This behavior can be explained
in a natural way by the polarization of the superconducting electrons upon the SC transition, i.e., an appearance of additional
induced magnetization within the SC, due to the proximity of the FM layer.
KeywordsProximity effects–Superconductors–Ferromagnets–Polarized neutron reflectometry–Waveguides
Journal of Superconductivity and Novel Magnetism 04/2012; 24(1):961-968. · 0.65 Impact Factor
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ABSTRACT: Magnesium hydride has high storage capacity (7.6 wt % H) but very slow sorption kinetics. Addition of catalytic phases on the surface as well as alloying with transition metals is known to improve the properties. In this study, the sorption kinetics of a 50-nm Mg layer and Mg-10%Cr-10%V layer, capped with a CrV/Pd bilayer catalyst, are compared using a combination of neutron reflectometry (NR), X-ray diffraction (XRD), and atomic force microscopy to elucidate the effects of alloying on the hydrogen storage properties of Mg at room temperature. From NR it is found that the Cr?V alloyed layer shows both a delay in expansion in the first absorption cycle and a delay in contraction in the first desorption, which indicates a delay in nucleation of MgD2 and formation of substoichiometric MgD2-δ, respectively. Compared to pure Mg, the kinetics are strongly improved as no blocking MgD2 layer is formed. XRD showed a strong reduction in the Mg grain size for the Cr?V alloyed layer after one cycle. For pure Mg,
The Journal of Physical Chemistry C 02/2012; 116(9):5868-5880. · 4.80 Impact Factor
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ABSTRACT: Magnesium hydride has high storage capacity (7.6 wt % H) but very slow sorption kinetics. Addition of catalytic phases on the surface as well as alloying with transition metals is known to improve the properties. In this study, the sorption kinetics of a 50-nm Mg layer and Mg-10%Cr-10%V layer, capped with a CrV/Pd bilayer catalyst, are compared using a combination of neutron reflectometry (NR), X-ray diffraction (XRD), and atomic force microscopy to elucidate the effects of alloying on the hydrogen storage properties of Mg at room temperature. From NR it is found that the Cr–V alloyed layer shows both a delay in expansion in the first absorption cycle and a delay in contraction in the first desorption, which indicates a delay in nucleation of MgD2 and formation of substoichiometric MgD2-δ, respectively. Compared to pure Mg, the kinetics are strongly improved as no blocking MgD2 layer is formed. XRD showed a strong reduction in the Mg grain size for the Cr–V alloyed layer after one cycle. For pure Mg, the grain size is almost unchanged although the film becomes nanocrystalline in the hydrided state. NR is shown to be highly sensitive to both the deuterium distribution as well as the layer thickness, which makes it a valuable tool for studying reaction mechanisms and quantification of the expansion of both crystalline and amorphous energy storage materials.
The Journal of Physical Chemistry C. 01/2012; 116(9):5868-5880.
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Journal of Physics D Applied Physics 01/2012; 45(40):405004. · 2.54 Impact Factor
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Solid State Communications 01/2012; 152:292-295. · 1.65 Impact Factor
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J. Demeter, A. Teichert,
K. Kiefer,
D. Wallacher,
H. Ryll,
E. Menéndez,
D. Paramanik,
R. Steitz,
C. Van Haesendonck,
A. Vantomme,
K. Temst
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ABSTRACT: A novel experimental facility to carry out simultaneous polarized neutron reflectometry (PNR) and anisotropic magnetoresistance (AMR) measurements is presented. Performing both techniques at the same time increases their strength considerably. The proof of concept of this method is demonstrated on a CoO/Co bilayer exchange bias system. Although information on the same phenomena, such as the coercivity or the reversal mechanism, can be separately obtained from either of these techniques, the simultaneous application optimizes the consistency between both. In this way, possible differences in experimental conditions, such as applied magnetic field amplitude and orientation, sample temperature, magnetic history, etc., can be ruled out. Consequently, only differences in the fundamental sensitivities of the techniques can cause discrepancies in the interpretation between the two. The almost instantaneous information obtained from AMR can be used to reveal time-dependent effects during the PNR acquisition. Moreover, the information inferred from the AMR measurements can be used for optimizing the experimental conditions for the PNR measurements in a more efficient way than with the PNR measurements alone.
Review of Scientific Instruments 02/2011; 82(3):033902-033902-7. · 1.37 Impact Factor
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C. Fleischmann,
F. Almeida,
J. Demeter,
K. Paredis, A. Teichert,
R. Steitz,
S. Brems,
B. Opperdoes,
C. Van Haesendonck,
A. Vantomme,
K. Temst
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ABSTRACT: We have investigated the correlation between magnetic and structural properties in exchange coupled polycrystalline CoO/Fe thin films. It has been found that an increase in interface roughness increases the exchange bias field as well as the coercivity. The magnetization reversal mechanism is also influenced by the interfacial morphology. Smooth interfaces are characterized by an asymmetric hysteresis loop, which is associated with domain wall motion for the first magnetization reversal after field cooling and spin rotation in all subsequent reversals. This asymmetry diminishes as the interface roughness increases, i.e., all magnetization reversals are dominated by spin rotation. Moreover, we have observed that the blocking temperature decreases with increasing interface roughness. We also report on a logarithmic time dependence of the magnetization which is different for both branches of the hysteresis loop of smooth CoO/Fe bilayers.
Journal of Applied Physics 07/2010; · 2.17 Impact Factor
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ABSTRACT: We present a neutron reflectometry study of deuterium absorption in thin films of Al containing Mg alloys capped with a Ta Pd, Ni Pd and Ti Pd catalyst bilayer. The measurements were performed at room temperature over the 0 1 bar pressure range under quasi equilibrium conditions. The modeling of the measurements provided a nanoscale representation of the deuterium profile in the layers at different stages of the absorption process. The absorption mechanism observed was found to involve spillover of atomic deuterium from the catalyst layer to the Mg alloy phase, followed by the deuteration of the Mg alloy. Complete deuteration of the Mg alloy occurs in a pressure range between 100 and 500 mbar, dependent on the type of bilayer catalyst. The use of a Ti Pd bilayer catalyst yielded the best results in terms of both storage density and kinetic properties
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ABSTRACT: An original approach for the formation of an exchange bias system is presented. Alternative to surface oxidation or deposition for the formation of Co CoO bilayer exchange bias systems, implantation of oxygen ions into Co films is applied. The implantation results in the formation of CoxOy embedded in a Co matrix. Comparison with noble gas implantation unambiguously demonstrates that the observed exchange bias effect is induced by the implanted oxygen. Opposed to bilayers formed by surface oxidation, the implantation results in a different morphology of the interface between Co and CoxOy and also gives rise to a radically different magnetization reversal mechanism
