BEGIN:VCALENDAR
VERSION:2.0
METHOD:PUBLISH
CALSCALE:GREGORIAN
PRODID:-//WordPress - MECv7.9.0//EN
X-ORIGINAL-URL:https://laboratoire-albert-fert.cnrs-thales.fr/
X-WR-CALNAME:Laboratoire Albert Fert
X-WR-CALDESC:CNRS - Thales
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-PUBLISHED-TTL:PT1H
X-MS-OLK-FORCEINSPECTOROPEN:TRUE
BEGIN:VEVENT
CLASS:PUBLIC
UID:MEC-2417dc8af8570f274e6775d4d60496da@laboratoire-albert-fert.cnrs-thales.fr
DTSTART:20261203T130000Z
DTEND:20261203T150000Z
DTSTAMP:20261013T111500Z
CREATED:20261013
LAST-MODIFIED:20261013
PRIORITY:5
SEQUENCE:20
TRANSP:OPAQUE
SUMMARY:PhD defense – William Bouckaert
DESCRIPTION:On Thursday, December 3, at 14 h (TRT Auditorium), William Bouckaert will defend his PhD thesis titled “Role of artificial topographic defects and in-plane magnetic fields in the nucleation and propagation of magnetic skyrmions”, supervised by Nicolas Reyren and Vincent Cros.\nJury members:\nAlexandra Mougin, CNRS Research Director, LPS, Université Paris-Saclay, Examiner and Chair of the Jury\nDaria Gusakova, CNRS Research Scientist, SPINTEC, Examiner\nMohamed Belmeguenai, Professor, Université Sorbonne Paris Nord, Reviewer\nOlivier Boulle, CNRS Research Scientist, SPINTEC, Reviewer\nMathieu Mivelle, CNRS Research Scientist, INSP, Sorbonne Université, Invited Member\nAbstract: \nMagnetic skyrmions are topological spin textures. They consist of metastable magnetization configurations in a ferromagnetic material. They are stabilized by a competition between several micromagnetic interactions, in particular the Dzyaloshinskii-Moriya interaction. The latter favors a given chirality, i.e. a preferred sense of rotation of the magnetization. Extensive work at the Albert Fert Laboratory has already enabled the stabilization of such textures through fine tuning of the layers adjacent to the ferromagnetic material and of the number of repetitions in the multilayer stack. The current-induced motion of such structures has also been made possible by strong spin-orbit coupling, which enables the conversion of a charge current into a spin current.\nOne of the objectives of my thesis was to study the physical mechanisms involved in skyrmion nucleation. To this end, new types of topographic defects were designed in our skyrmion tracks: first, dots deposited on the substrate by focused electron-beam-induced deposition (FEBID), before deposition of the multilayer; second, holes milled directly through the multilayer using a focused ion beam (FIB). These nucleation sites make it possible to quantitatively tune the current threshold for nucleation. COMSOL simulations were used to understand the effect of their dimensions on the current-density distribution responsible for the nucleation.\nWe also showed that an external in-plane magnetic field provides an important additional degree of freedom for the nucleation probability. MuMax3 simulations enabled us to identify the mechanisms involved in this dependence and to relate it to the role of the damping-like (DL) spin-orbit torque (SOT).\nAnother important focus of my thesis was the study of the field-like component of the spin-orbit torque, and more generally the effect of an external in-plane magnetic field on the dynamics of skyrmions and domain walls. A field parallel to the current density was found to have only a weak effect on skyrmion dynamics, whereas a field perpendicular to the current showed a strong effect on both the magnitude and direction of their velocity, thereby modifying the skyrmion Hall angle (SkHA). The results showed that this dependence varies with current density. Domain-wall velocity was found to be even more strongly dependent on a transverse magnetic field.\nMuMax3 simulations were used to investigate these effects. We identified their origin and qualitatively reproduced the dependence of skyrmion velocity, showing a reorganization of their internal texture in all three spatial dimensions. These simulations also enabled us to study the strong dependence of domain-wall velocity on the external transverse field and to relate it to the DL component of the SOT.\nSkyrmion motion was also controlled in a second way: the FIB and FEBID techniques were used either to deposit a line on the substrate beneath the multilayer or to etch a line through the multilayer, parallel to the current, thereby guiding the skyrmions. Both techniques make it possible to reduce, or even suppress, the effect of the SkHA. The latter is responsible for the deflection of skyrmion trajectories towards the edge of the track, where they can be destroyed, thereby limiting their use in computing devices.\nFinally, the thermal conductivity of several substrates was investigated. We showed that a high-resistivity silicon (Si-HR) substrate, because of its higher thermal conductivity, allows larger current densities to be used for skyrmion motion before widespread nucleation occurs along the track, thereby enabling skyrmion velocities close to 150 m/s, a record value for this multilayer.\n
URL:https://laboratoire-albert-fert.cnrs-thales.fr/en/events/phd-defense-maxime-ardisson-857-916/
CATEGORIES:PhD defence
END:VEVENT
END:VCALENDAR