PhD thesis starting in October 2025
Fe-based nanorods for the fabrication of rare-earth free magnets
Supervisors :
· Lise-Marie Lacroix, LPCNO.lmlacroi@insa-toulouse.fr
· Guillaume Viau, LPCNO.gviau@insa-toulouse.fr
· Julian Carrey, LPCNO.julian.carrey@insa-toulouse.fr
Magnetic materials play a major role in the currentenergy transition. However, thedevelopment of sustainable yet performant permanentmagnets, without critical elementssuch as rare-earths (RE), remains a challenge [1].A promising alternative to Nd-based magnetsconsists of a nanostructured material made of Fe16N2nanorods exhibiting controlleddimensions (diameter < 20 nm; length > 100 nm). This gathers two scientific challenges : first,the Fe16N2phase is metastable and thus hard to stabilize; second, the chemical synthesis ofanisotropic Fe-based objects has never been reported yet.In the framework of a large project gathering 5 laboratories with complementary expertise, anew approach consisting in the oriented attachmentof preformed Fe nanoparticles (NPs) andtheir controlled nitridation is proposed using a high-frequency alternating magnetic field asdriving force (Figure 1). We will take advantage ofi) the chain alignment of the NPs undermagnetic field and ii) the induced heating to promote their coalescence [2]
Figure 1. a) TEM image of the Fe(0) nanoparticles.b) Schematic view of the strategy proposed for theorientedattachment of Fe(0) NPs and their nitridation undera high-frequency alternating magnetic field
The LPCNO has a strong expertise in the synthesis of metallic Fe-based NPs using anorganometallic approach [3,4] and has been workingfor almost 10 years on the developmentof rare-earth-free magnets using a directed assembly approach of NPs [5]. The aim of this PhDwork will be to characterize the heat power of NPsas a function of their shape and chemicalstate, design and fabricate a reactor to allow foran in-situ characterization using X-Rayscattering (SAXS and WAXS) and X-Ray absorption (XAS), analyze the large data set obtainedwith machine learning tools which are currently being developped at LPCNO. Understandingthe mechanism will allow optimizing the reaction condition to eventually yield Fe16N2nanorods.
For such a pluridisciplinary thesis, we are lookingfor a candidate with a physics/engineeringbackground and experience on characterization techniques (XRD, TEM, SAXS). Programmingand/or chemical synthesis will be a plus. The person is expected to demonstrate curiosity andscientific rigor as well as good communication andwriting skills.
[1] Gutfleisch, O.et al. Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient.Adv.Mater.2011,23, 821. [2]J. M. Asensio et al. To Heat or not to Heat: a study of the performances of Iron Carbide Nanoparticlesin Hyperthermia,Nanoscale,2019,11, 5402 ; [3] Lacroix, L.-M. et al. Iron NanoparticlesGrowth in Organic Super-Structures,J.Am. Chem. Soc.,2009,131, 549 [4] Garnero, C. et al. Chemical Ordering in Bimetallic FeCo Nanoparticles : from a direct chemicalsynthesis to application as efficient high frequency magnetic material,Nanoletters201919, 1379 [5] Moritz, P.et alMagnetophoresis-Assisted Capillary Assembly: a Versatile Approach for Fabricating Tailored 3D MagneticSupercrystals,ACS Nano2021,15, 5096