The search for thermoelectric materials is an active topic, and promising new families such as chalcogenides have emerged in recent years with the figure of merit ZT reaching 1 or above. One of the possible tuning parameters of ZT in chalcogenides containing transition-metal cations is magnetism which can modify the transport parameters through a modification of the band structure and/or a modification of the entropy of the material. The thermal conductivity can also potentially be modified by magnetism. Even if promising interplay between thermoelectric properties and magnetism has already been demonstrated in some oxides and sulfides, a detailed understanding of these phenomena is still lacking. The aim of the project is to investigate the interplay between carriers, spins and phonons in three selected families of chalcogenides, guided by the input from Density Functional Theory (DFT). This will subsequently allow the optimization of the thermoelectric properties of these materials. The project will focus on three families of materials, the pentlandites, the pyrites and the thiospinels. Using these three different families, several parameters will be investigated. First in the case of pentlandites, the impact of a gradual introduction of magnetism in a Pauli metal and how the associated localization can contribute to an optimized power factor will be analyzed. For pyrites, the power factor is already very promising and several doping strategies will be followed to reduce the lattice part of the thermal conductivity. Finally, in thiospinels, DFT calculations will serve as a guide to define the best electronic and magnetic structures for optimizing the power factor and reducing the thermal conductivity. The project relies on a very close collaboration between DFT experts from CPHT and specialists in thermoelectric materials and magnetism in CRISMAT and GPM. A systematic screening of the thermoelectric properties of these materials will be performed by state of the art DFT calculations, and the transport properties of the most promising materials will be calculated, both for the electronic and phononic parts. The materials will be simultaneously synthesized, structurally characterized (both for chemical composition and possible disorder phenomena by x-Ray diffraction and transmission electron microscopy) and their thermoelectric properties measured in CRISMAT in a large range of temperatures (2K – 1000K) and up to 14T. Beyond studies of the magnetic properties by standard SQUID magnetometry, the magnetism will be investigated in GPM at the local scale by Mössbauer spectrometry, a powerful technique to probe magnetism and disorder and obtain crucial information about the magnetic characteristics such as oxidation state, spin configuration or magnetic moment direction at a given crystallographic site. The DFT calculations and experimental results will benefit from each other reciprocally throughout the project. This will allow us to define new pathways to optimize the figure of merit of these magnetic chalcogenides. This project fits perfectly in the ‘Sciences de base pour l’Energie’ committee as it will broaden the knowledge on how magnetism and spins can contribute to thermopower and thermal conductivity. It will help in the design of new thermoelectric materials, and will define original ways to tune the magnetic properties to optimize thermoelectric properties. These materials will have potential applications in the field of energy harvesting. The project will also shed more light on factors that affect thermal conductivity, a critical quantity in many energy applications, such as thermal barriers (small thermal conductivity) to reduce parasitic heat transfers or thermal management (with large thermal conductivity) for electronic devices.