Reference : UPR8521-FRAVER-002
Workplace : PERPIGNAN
Date of publication : Tuesday, September 20, 2022
Scientific Responsible name : Francois Vernay
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 17 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Magnetic hyperthermia, which is the object of an important research activity in the field of magnetic nanomaterials, consists in converting into heat the magnetic energy absorbed by magnetic nanoparticles (NPM) under the effect of an oscillating external field. Given the nanometric scale involved, devices based on this process can achieve a temperature rise both targeted and highly localized. The applications are mainly in catalysis and in medicine for the treatment of cancerous tumors. The systems concerned are either dispersed colloidal solutions (ferrofluids) or high concentration assemblies, or even aggregates of NPM (multi cores nanosystems). Although magnetic hyperthermia has been studied extensively, the fine description of the heat diffusion, and in particular of the temporal and spatial temperature profile in the vicinity of the NPMs is lacking. This holds also for the understanding of the optimization of the process in terms of the relevant structural parameters of the NPM assemblies. The NPM being magnetic monodomain objects, the dominant interactions between NPM are of dipolar character to which one must add, in addition to the external field, a magnetocrystalline anisotropy term. Hyperthermia efficiency is defined through the specific absorption rate (SAR) which is calculated by the hysteresis loop along one cycle or the imaginary part of the magnetic susceptibility, χ''(ω). The purpose of the thesis is in a first step to determine by numerical simulations the SAR of NPM aggregates and assemblies as a function of their structure, i.e. volume fraction, shape and size, in order to optimize the SAR. These simulations will use a dynamic Monte Carlo scheme to track metastable states. We will consider time quantified Monte Carlo (TQMC)  and kinetic Monte Carlo (KMC)  methods whose codes will be derived from the version developped before for equilibrium properties . A micromagnetic type of approach using finite elements (FEM) will be then considered in order to introduce coupling effects between the NPM and the host matrix. In a second step, sem-analytical approaches will be examined, essentially based on perturbation developments, valid a priori for weak dipolar interactions . Finally, a study of the local temperature profile will be considered, based on a heat diffusion equation, using the SAR as a source term and a Newton coefficient for the NPM/matrix coupling. The thesis is part of a global project funded by the ANR and includes an experimental part from the synthesis of NPM samples to magnetic and SAR measurements. Consequently, a comparison between theory and experiments is underlying the whole thesis work.
 X.-Y. Cheng et al. Prhys. Rev. Lett. 96, 067208 (2006).
 T.-J. Fal et al. Phys. Rev. B 87, 064405 (2013).
 V. Russier et al. Phys. Rev. B. 102, 174410 (2020).
 J.-L. Déjardin et al. J. Appl. Phys. 121, 203903 (2017).
The thesis will be carried out within the framework of the ANR NanoHype project and will involve two partners of the consortium. One is located at the ICMPE in Thiais (CNRS and University Paris-Est Créteil), and the other is located in Perpignan, at the PROMES laboratory (CNRS and University of Perpignan Via Domitia). The PI in Thiais is Dr. Russier.
Constraints and risks
None (Thesis in condensed matter theory)
We talk about it on Twitter!