Domain wall propagation and pinning induced by current pulses in cylindrical modulated nanowires.

The future developments in 3D magnetic nanotechnology require the control of domain wall dynamics by means of current pulses. While this has been extensively studied in 2D magnetic strips (planar nanowires), few reports on this exist in cylindrical geometry, where Bloch point domain walls are expected to have intriguing properties. Here, we report an investigation on cylindrical magnetic Ni nanowires with geometrical notches. An experimental work based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with photoemission electron microscopy (PEEM) indicates that large current densities induce domain wall nucleation, while smaller currents move domain walls preferably antiparallel to the current direction. In the region where no pinning centers are present, we found a domain wall velocity of about 1 km s-1. Thermal modelling indicates that large current densities temporarily raise the temperature in the nanowire above the Curie temperature, leading to nucleation of domain walls during the system cooling. Micromagnetic modelling with a spin-torque effect shows that for intermediate current densities, Bloch point domain walls with chirality parallel to the Oersted field propagate antiparallel to the current direction. In other cases, domain walls can be bounced from the notches and/or get pinned outside their positions. We thus found that current is not only responsible for domain wall propagation, but also is a source of pinning due to the Oersted field action.

Evidence of Skyrmion-Tube Mediated Magnetization Reversal in Modulated Nanowires.

Magnetic nanowires, conceived as individual building blocks for spintronic devices, constitute a well-suited model to design and study magnetization reversal processes, or to tackle fundamental questions, such as the presence of topologically protected magnetization textures under particular conditions. Recently, a skyrmion-tube mediated magnetization reversal process was theoretically reported in diameter modulated cylindrical nanowires. In these nanowires, a vortex nucleates at the end of the segments with larger diameter and propagates, resulting in a first switching of the nanowire core magnetization at small fields. In this work, we show experimental evidence of the so-called Bloch skyrmion-tubes, using advanced Magnetic Force Microscopy modes to image the magnetization reversal process of FeCoCu diameter modulated nanowires. By monitoring the magnetic state of the nanowire during applied field sweeping, a detected drop of magnetic signal at a given critical field unveils the presence of a skyrmion-tube, due to mutually compensating stray field components. That evidences the presence of a skyrmion-tube as an intermediate stage during the magnetization reversal, whose presence is related to the geometrical dimensions of the cylindrical segments.

Plasmonic coupling in closed-packed ordered gallium nanoparticles.

Plasmonic gallium (Ga) nanoparticles (NPs) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narrowing the NP size distribution among other factors. With this purpose, our last work demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region. The quantitative analysis of the optical properties by spectroscopic ellipsometry confirmed an outstanding improvement of the LSPR intensity and full width at half maximum (FWHM) due to the imposed ordering. Here, by engineering the template dimensions, and therefore by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions. More interestingly, the factors that cause this optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. The results allow us to conclude that the plasmonic coupling between NPs originated in the ordered systems is the main cause for the optimized optical response.

Investigation of split CoFeB/Ta/CoFeB/MgO stacks for magnetic memories applications.

We report on the static and dynamic magnetic properties of W/CoFeB/Ta/CoFeB/MgO stacks, where the CoFeB layer is split in two by a 0.3 nm-thick Ta "dusting" layer. A total CoFeB thickness between 1.2 and 2.4 nm is studied. Perpendicular magnetic anisotropy is obtained for thickness below 1.8 nm even at the as-deposited stacks, and it is enhanced after annealing. Saturation magnetization is 1520 (1440) kA/m before (after) annealing, increased compared to non-split CoFeB layers. Ferromagnetic resonance measurements show that high magnetic anisotropy energy may be achieved (effective anisotropy field 0.571 ± 0.003 T), combined to a moderate Gilbert damping (0.030 ± 0.001). We argue that the above characteristics make the split-CoFeB system advantageous for spintronics applications.

Multisegmented Nanowires: a Step towards the Control of the Domain Wall Configuration.

Cylindrical nanowires synthesized by controlled electrodeposition constitute excellent strategic candidates to engineer magnetic domain configurations. In this work, multisegmented CoNi/Ni nanowires are synthesized for tailoring a periodic magnetic structure determined by the balance between magnetocrystalline and magnetostatic energies. High-resolution Transmission Electron Microscopy confirms the segmented growth and the sharp transition between layers. Although both CoNi and Ni segments have similar fcc cubic crystal symmetry, their magnetic configuration is quite different as experimentally revealed by Magnetic Force Microscopy (MFM) imaging. While the Ni segments are single domain with axial magnetization direction, the CoNi segments present two main configurations: a single vortex state or a complex multivortex magnetic configuration, which is further interpreted with the help of micromagnetic simulations. This original outcome is ascribed to the tight competition between anisotropies. The almost monocrystalline fcc structure of the CoNi segments, as revealed by the electron diffraction patterns, which is atypical for its composition, contributes to balance the magnetocrystalline and shape anisotropies. The results of MFM measurements performed under in-plane magnetic field demonstrate that it is possible to switch from the multivortex configuration to a single vortex configuration with low magnetic fields.

Doubling of the magnetic energy product in ferromagnetic nanowires at ambient temperature by capping their tips with an antiferromagnet.

We present an approach to prepare free-standing tips of micrometer-long nanowires electrodeposited in anodic aluminum oxide nanopores. Such open tips can be further processed, e.g. for vertical interconnects of functional layers or for tailoring the magnetization reversal of ferromagnetic nanowires. The magnetic switching of nanowires is usually initiated by vortex or domain formation at the nanowire tips. We show that coating the tips of Fe30Co70 nanowires (diameter 40 nm, length 16 µm) with thin antiferromagnetic Fe50Mn50 capping layers (thickness ≈10 nm) leads to magnetic hardening with a more than doubled energy product at ambient temperature.

Co/Au multisegmented nanowires: a 3D array of magnetostatically coupled nanopillars.

Arrays of multisegmented Co/Au nanowires with designed segment lengths and diameters have been prepared by electrodeposition into aluminum oxide templates. The high quality of the Co/Au interface and the crystallographic structure of Co segments have determined by high-resolution transmission electron microscopy. Magnetic hysteresis loop measurements show larger coercivity and squareness of multisegmented nanowires as compared to single segment Co nanowires. The complementary micromagnetic simulations are in good agreement with the experimental results, confirming that the magnetic behavior is defined mainly by magnetostatic coupling between different segments. The proposed structure constitutes an innovative route towards a 3D array of synchronized magnetic nano-oscillators with large potential in nanoelectronics.

[Medical certificates for driving licence, for safety belt]. / Certificats en matière de permis de conduire, de port de ceinture de sécurité.

Concerning driving licence, there are two groups of medical criteria determined by "arrêté royal" according to the type of driving licence. In order to be declared a qualified driver, the candidate has to fulfil the minimal norms determined in the annex 6 of the "arrêté royal" of 23 March 1998 concerning visual faculty and must be free from any disease or physical abnormality or psychological disorders likely to jeopardize the security while driving. For the candidates of the first group, only an honor statement is required. If the candidate does not know if he plainly fulfils the norms to sign that statement, he has to go and see a physician of his own choice. According to the candidate's pathology, the doctor may refer him to a specialist. The latter will have one or several complementary tests done. According to the medical examinations' result, the physician will then make the statement--total ability, partial ability or disability--and fill in the form provided to that end. Concerning the exemption of the use of safety belt, the "arrêté royal" of 13 May 1975, still applicable today, does not determine any criterium. The physician is only required to state that there is a serious medical contra-indication against the use of safety belt.