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DTSTART;TZID=Europe/Paris:20260619T140000
DTEND;TZID=Europe/Paris:20260619T160000
DTSTAMP:20260617T115337
CREATED:20260529T145132Z
LAST-MODIFIED:20260529T145509Z
UID:10000175-1781877600-1781884800@sfp-alpes.fr
SUMMARY:Soutenance de Thèse de Marco BIAGI (IRIG/Spintec)
DESCRIPTION:Exploration of orbital-to-spin conversion materials and integration in 3-terminal spin-orbit torque magnetic tunnel junctions\nRésumé : \nThe development of electrically controlled nanomagnets for spintronic applications\, particularly non-volatile magnetic memories (MRAM)\, is attracting strong interest due to the limitations of CMOS-based memories such as SRAM and eDRAM. Spin–orbit torque (SOT) MRAMs are promising candidates for addressing SRAM specifications; however\, current materials still suffer from limited efficiency and high resistivity\, leading to unmet write-current requirements. Recently\, studies have highlighted orbital phenomena as a potential route to enhance SOT efficiency\, owing to their larger magnitudes and availability in a broader set of materials. However\, orbital currents do not couple to magnetization in the absence of spin–orbit coupling\, requiring an orbital-to-spin conversion layer\, which motivates studies of conversion mechanisms and associated physics. \nIn this PhD work\, we evaluate promising orbital/HM/FM material systems for SOTMRAM applications. We present a comprehensive study of Ru/HM/FeCoB and Ta/W/ FeCoB systems\, where Ru and Ta act as orbital current sources\, while Ta\, W\, and Pt serve as orbital-to-spin conversion layers. Ru is predicted to exhibit one of the largest orbital Hall angles among transition metals while maintaining low resistivity. Ta\, a heavy metal with a large spin Hall effect\, is predicted to exhibit an orbital Hall angle approximately one order of magnitude larger than its spin counterpart. When a heavy metal is used as a conversion layer\, multiple spin-current contributions can coexist and add linearly to the total effective spin Hall conductivity\, potentially enhancing the overall SOT efficiency. \nWe characterized key parameters relevant to SOT magnetic tunnel junctions (MTJ) devices\, including saturation magnetization\, effective anisotropy field\, and resistivity\, and we quantified damping-like (ξDL) and field-like (ξFL) SOT efficiencies as a function of orbital and conversion layer thickness\, both in as-deposited and 300°C annealed samples. These metrics are benchmarked against reference HM/FeCoB systems to isolate the effect of the additional orbital layer. For Ru/Ta and Ru/W stacks\, limited enhancement ξFL of ξDL is observed relative to reference systems. In contrast\, Ru/Pt exhibits a twofold increase in ξDL compared to Pt alone. This difference is attributed to the stronger SOC in Pt\, which enables more efficient orbital-to-spin conversion. The independence of ξDL on Ru thickness further suggests an interfacial origin of the orbital contribution in Ru/Pt. However\, thermal annealing strongly degrades ξDL\, limiting its applicability for SOT-MRAM. In Ta/W systems\, we observe a strong enhancement of ξDL by a factor of 4.4 relative to Ta and 3.2 relative to W. A parallel-resistor model indicates that conventional SHE contributions cannot fully account for this increase\, pointing to an additional orbital-related mechanism. Extending the study to 400 °C annealing shows that ξDL remains largely stable\, indicating good thermal robustness while maintaining perpendicular magnetic anisotropy. \nLeveraging these advantages\, we further integrate the Ta/W system into SOT-MTJs and benchmark it against standard W-based MTJs. We investigate the pulse-length dependence of the critical switching current and provide a first demonstration of integrated orbital-to-spin conversion in SOT-MTJs. Ta/W devices exhibit switching currents comparable to W-based devices but have a lower switching current density and improved perpendicular magnetic anisotropy stability. Finally\, we present a proof-of-concept for vertical non-local switching of SOT-MTJ using orbital torques\, simplifying bottom-pinned SOT-MRAM fabrication. Overall\, these results demonstrate that orbital physics can be exploited to enhance SOT-MTJ performance\, simplify fabrication\, and provide a promising route toward scalable bottom-pinned MRAM technologies. \nPlus d’information : https://www.spintec.fr/phd-defense-exploration-of-orbital-to-spin-conversion-materials-and-integration-in-3-terminal-spin-orbit-torque-magnetic-tunnel-junctions/ \nPour suivre la soutenance ​​​en visioconférence : https://univ-grenoble-alpes-fr.zoom.us/j/98769867024?pwd=dXNnT3RMeThjYStybGVQSUN0TVdJdz09 \n_ \n\n\nP​resential access to the confere​nce room at CEA in Gre​​noble requires an entry authorization\, request to admin.spintec@cea.fr
URL:https://sfp-alpes.fr/event/soutenance-de-these-marco-biagi-irig-spintec/
LOCATION:CEA – Salle de Séminaire IRIG (1005 – 445)\, Laboratoire Irig/Spintec\, salle de séminaire 445\, bâtiment 1005\, CEA-Grenoble\, Grenoble
CATEGORIES:Soutenance,Soutenance de Thèse
ORGANIZER;CN="IRIG - CEA":MAILTO:odile.rossignol@cea.fr
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260622T133000
DTEND;TZID=Europe/Paris:20260622T153000
DTSTAMP:20260617T115337
CREATED:20260604T143528Z
LAST-MODIFIED:20260604T143528Z
UID:10000188-1782135000-1782142200@sfp-alpes.fr
SUMMARY:Soutenance de Thèse de Khadeeja MUBASHIRA (CEA-Irig/IBS)
DESCRIPTION:Étude de la séparation de phase de la phosphoprotéine du virus de la rage et de sa régulation par LC8\nRésumé : \nRabies virus (RABV) replication occurs in cytoplasmic\, membrane-less compartments known as Negri bodies (NBs)\, formed through liquid-liquid phase separation (LLPS) of viral components. The phosphoprotein (RABV P) is a central\, intrinsically disordered scaf fold of the viral replication machinery. This thesis investigates the structural\, biophysical\, and dynamic properties of RABV P\, with emphasis on its phase separation behavior and interactions with molecular partners. To enable this\, recombinant expression and purification protocols were optimized to produce stable\, high-quality protein samples for reproducible analyses. \nWe first characterized the intrinsic phase behavior of RABV P in vitro. The protein undergoes thermoresponsive LLPS with a lower critical solution temperature (LCST)\, forming reversible condensates within a narrow range of protein and salt concentrations. This process is driven by multivalent interactions within a heterogeneous ensemble of conformations\, where dimers assemble into higher-order oligomers prior to phase separation. The resulting phase diagram reveals a complex\, reentrant system governed by a balance between electrostatic repulsion and attractive dipole-dipole interactions. \nThe role of ionic conditions was further examined. While NaCl induced reentrant phase separation\, LLPS strongly depended on ion identity rather than ionic strength alone. Chloride salts promoted condensate formation\, whereas bromide salts did not\, indicating ion-specific (Hofmeister-type) effects. Systematic trends showed that fluoride enhances phase separation\, while cation effects are weaker. Divalent ions also promoted LLPS\, highlighting valency contributions. Chemical perturbations confirmed that condensates are stabilized by weak interactions: 1\,6-hexanediol partially disrupted droplets\, whereas ATP fully dissolved them. Notably\, RABV P intrinsically phase separates even in water\, modulated by pH\, protein concentration\, and ionic conditions. \nTime-resolved small-angle X-ray scattering (SAXS) revealed the structural evolution underlying LLPS. Following a temperature jump\, RABV P undergoes a hierarchical assembly process\, transitioning from dispersed species to larger structures. Early conformational rearrangements precede the formation of intermediate clusters\, followed by growth into larger assemblies. These structures remain disordered and liquid-like\, supporting a multistep nucleation-and-growth mechanism. \nThe host protein LC8 was investigated as a regulator of RABV P condensation. LC8 binds a conserved motif in RABV P with high affinity\, forming a defined complex and partitioning into condensates. Functionally\, LC8 enhances phase separation by increasing condensate size\, enriching RABV P in the dense phase\, and broadening the phase-separation window. It shifts phase boundaries toward lower concentrations and temperatures while preserving liquid-like properties. These results indicate that LC8 actively promotes condensation by stabilizing interaction-competent conformations and enhancing intermolecular connectivity. \nTo assess whether LC8 can compensate for intrinsic multivalency\, a truncated RABV P lacking the dimerization domain was analyzed. Although LC8 bound this construct\, the interaction was weaker and failed to restore robust phase separation. Only weak condensation was observed under crowding conditions\, demonstrating that LC8 cannot substitute for the native dimerization-driven multivalency.\nOverall\, this work establishes RABV P as a finely tuned multivalent scaffold whose phase behavior arises from the interplay of intrinsic disorder\, ion-specific effects\, and hierarchical assembly. LLPS emerges as a multistep\, non-ideal process rather than a simple binary transition. LC8 acts as a key host regulator that enhances phase separation without altering condensate dynamics\, while intrinsic multivalency remains essential. These findings provide a mechanistic framework for understanding viral condensate formation and highlight potential avenues for antiviral intervention. \n_ \nContact : alain.farchi@cea.fr
URL:https://sfp-alpes.fr/event/soutenance-de-these-de-khadeeja-mubashira-cea-irig-ibs/
LOCATION:Amphi A de Biologie\, Rue de la Piscine\, Saint-Martin-d'Hères\, 38400\, France
CATEGORIES:Soutenance,Soutenance de Thèse
ORGANIZER;CN="IRIG - CEA":MAILTO:odile.rossignol@cea.fr
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20260626T140000
DTEND;TZID=Europe/Paris:20260626T160000
DTSTAMP:20260617T115337
CREATED:20260529T140204Z
LAST-MODIFIED:20260529T140307Z
UID:10000170-1782482400-1782489600@sfp-alpes.fr
SUMMARY:Soutenance de Thèse de Henri GRÖGER (Irig/IBS)
DESCRIPTION:Structural and functional characterisation of the vaccinia virus PLD- fold endonuclease K4\, telomere-binding protein i1 and the DNA polymerase complex E9A20D4\nRésumé : \n\nPoxviruses\, such as the vaccinia virus (VACV) and the monkeypox virus\, are large\, enveloped dsDNA viruses from the orthopoxvirus genus that replicate entirely within the host cytoplasm. The 2022 and 2024 outbreaks of mpox\, caused by clade IIb and Ib\, respectively\, have revealed the lack of efficient antivirals and underlined the urgency of understanding poxvirus biology. The poxvirus genome is flanked by short\, inverted complementary hairpin telomeres that feature mismatched bases and insertions essential for viral replication. ​\n​\nThis thesis presents the structural and functional characterisation of three proteins central to poxvirus DNA metabolism : the E9A20D4 DNA polymerase holoenzyme\, and two telomere-interacting proteins\, the PLD-fold nuclease K4 and I1. The project initially focused on the VACV polymerase holoenzyme\, but was reoriented towards the telomere-interacting proteins following the publication of numerous competing mpox polymerase structures. ​\n​\nHaving established that VACV polymerase activity requires K+ and is inhibited by Na+\, I undertook a structure determination of the E9A20D4 polymerase holoenzyme bound to template DNA\, primer and incoming nucleotide in the presence of K+\, using single-particle cryogenic electron microscopy (cryo-EM). I obtained both the structure of the complex E9exo−A20D4 as well as the structure of E9exo− alone bound to the primer-template DNA. The structures in the presence of K+ appear identical to published structures in the presence of Na+. However\, I identified an ion binding site in the exonuclease domain of E9. The thumb domain is disordered in the DNA-free structure\, partially disordered in DNA-bound E9 and ordered in the holoenzyme-DNA complex. SAXS data indicate conformational flexibility\, with more open conformations of E9A20D4 lacking an E9-D4 interface\, while mass photometry reveals partial dissociation of E9A20D4 at low concentrations\, even in the presence of substrate. ​\n​\nUsing cryo-EM\, I report the first structures of K4 in both apo and DNA-bound states\, revealing that the active site is occluded by an orthopoxvirus-specific C-terminal extension of the PLD fold that is displaced upon DNA binding. Biochemical characterisation demonstrates that K4 functions as a DNA-specific endonuclease with a preference for single-stranded DNA and hairpin loops. ​\n​\nI also report the first cryo-EM structure of I1 bound to DNA. I1 is known to bind to viral telomeres and is essential for virion maturation. Cryo-EM data showed the presence of dimers where the head domains 2 and 3 of I1 interact with the DNA duplex through electrostatic interactions\, while the N-terminal domain predicted to be α-helical remains disordered. In solution\, isolated I1 or I1 bound to DNA forms higher-order assemblies\, predominantly tetramers\, but also octamers. ​\n​\n​ Altogether\, these findings substantially advance the molecular understanding of poxvirus biology\, providing a foundation for future mechanistic studies and the rational development of antiviral strategies against emerging orthopoxvirus infections.\n​​\n\n\nLes séminaires et soutenances sont ouverts à tous\, notez toutefois que l’accès au campus EPN nécessite un avis de rendez-vous. Merci de remplir ce formulaire  et de l’adresser\, plus de 48h à l’avance\, à ibs.seminaires@ibs.fr. Pensez à vous munir d’une pièce d’identité le jour de votre visite.\n\n  \n  \n  \n  \n  \n 
URL:https://sfp-alpes.fr/event/soutenance-de-these-de-henri-groger-irig-ibs/
LOCATION:Salle des séminaires du CIBB\, EPN Campus - 71 avenue des Martyrs\, Grenoble\, 38000\, France
CATEGORIES:Soutenance,Soutenance de Thèse
ORGANIZER;CN="IRIG - CEA":MAILTO:odile.rossignol@cea.fr
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