Role of microstructure in the performance of sintered SmFe12-xMx magnets
The TR-Fe12 type and the ThMn12 quadratic structure have very interesting intrinsic properties (magnetocrystalline anisotropy HA, saturation magnetization Ms and Curie temperature TC). They are considered as the best alternative to NdFeB magnets, offering TR savings of around 35% by weight.
For Sm-based compounds of the Sm(Fe,Ti,V)12 type, it has been demonstrated that the formation of a phase at grain boundaries by the addition of additive elements can significantly increase coercivity up to 1.4 T. However, remanence remains low, below 1 T, which limits the field of application of these magnets. In this thesis, we propose a study of addition elements likely to increase both the remanence and coercivity of TR-Fe12 type magnets.
For Sm-Fe12 compounds, the additions studied will aim to increase the remanence of these magnets by reducing the rate of Fe substitution by stabilizing elements. They will also promote the formation of paramagnetic phases at grain boundaries to enhance coercivity.
Theoretical studies of orbitronic and spin-orbit phenomena in heterostructures comprising van der Waals materials, metals and oxides
The proposed PhD thesis aims at finding the best-unexplored combinations of transition metals, oxides and 2D materials (transition metal dichalcogenides, 2D magnets, graphene…) to help optimizing and providing scientific underpinnings of next generation energy efficient spintronic storage and memory devices based on emerging fields of spin-orbitronics and orbitronics. The latter is a fascinating new field of research that exploits orbital currents and their interaction with spin currents mediated by spin-orbit coupling.
Namely, using first principles calculations combined with tight-binding approach and linear response theory, we will screen the potential of aforementioned heterostructures not only for spin-orbit phenomena such as Dzyaloshinskii-Moriya interaction (DMI), perpendicular magnetic anisotropy (PMA) and spin-charge interconversion based on Rashba and Rashba-Edelstein effects (REE), but also focus on Orbital Rashba Edelstein Effect (OREE). Furthermore, the mechanisms of control of these phenomena via external stimuli (strain, external electric and magnetic fields) will be investigated as well. These studies will help finding optimal material combination to tune DMI, PMA and spin-charge interconversion efficiency to help optimizing spintronic devices making thereby a significant contribution to the development of sustainable microelectronics.
The PhD will be based on a multiscale approach including ab initio, tight-binding and atomistic approaches thus highly motivated candidate with a good background in solid state physics, condensed matter theory and numerical simulations is required. He/she will perform his/her calculations on Spintec computational cluster nodes using first-principles packages based on density functional theory (DFT) combined with other simulation codes/tools. Results obtained will be carefully analyzed with the possibility of publication in international scientific journals. Strong collaboration with labs in France (CEA/LETI, Laboratoire Albert Fert (CNRS,Thales), Aix-Marseille Univ…) and abroad (ICN2-Barcelona, PGI Forschungszentrum Jülich, Osaka University) are previewed.
Numerical twin for the Flame Spray Pyrolysis process
Our ability to manufacture metal oxide nanoparticles (NPs) with well-defined composition, morphology and properties is a key to accessing new materials that can have a revolutionary technological impact, for example for photocatalysis or storage of energy. Among the different nanopowders production technologies, Flame Spray Pyrolysis (FSP) constitutes a promising option for the industrial synthesis of NPs. This synthesis route is based on the rapid evaporation of a solution - solvent plus precursors - atomized in the form of droplets in a pilot flame to obtain nanoparticles. Unfortunately, mastery of the FSP process is currently limited due to too much variability in operating conditions to explore for the multitude of target nanoparticles. In this context, the objective of this thesis is to develop the experimental and numerical framework required by the future deployment of artificial intelligence for the control of FSP systems. To do this, the different phenomena taking place in the synthesis flames during the formation of the nanoparticles will be simulated, in particular by means of fluid dynamics calculations. Ultimately, the creation of a digital twin of the process is expected, which will provide a predictive approach for the choice of the synthesis parameters to be used to arrive at the desired material. This will drastically reduce the number of experiments to be carried out and in consequence the time to develop new grades of materials
Development of thin film negative electrodes for Li-free all-solid-state batteries
The aim of this work is to develop 'Li-free' negative electrodes for new generations of high energy density all-solid-state lithium batteries. The function of this type of electrode is to provide a significant gain in energy density in the battery, to facilitate its manufacture by eliminating the need to handle lithium metal and, most importantly, to enable the formation of a homogeneous, dendrite-free lithium film when the battery is charged.
These electrodes will be based on the functionalisation of a metal collector with thin-film materials comprising at least one lithiophilic material (typically a compound that can be alloyed with lithium) and an inorganic ionic conductor. These electrodes are prepared by physical vacuum deposition processes such as sputtering or thermal evaporation. It will therefore be necessary to study the influence of the composition and structure of the lithiophilic layer on the nucleation and growth mechanism of the lithium film and on the evolution of the electrode during charge/discharge cycles. The role of chemical/mechanical interactions with the ionic conducting layer will also be investigated.
This work, which is part of a national CEA/CNRS joint project, will be carried out at the CEA Tech site in Pessac, which has a full range of vacuum deposition and thin film characterisation equipment, in close collaboration with ICMCB CNRS in Bordeaux. It will benefit from the many characterisation resources (confocal optical microscopy, SEM/cryo FIB, ToF-SIMS, SS-NMR, µ-XRD, AFM,...) available in the various partner laboratories involved in the project.