Les alliages Heusler de type Ni-Mn-X (X=In, Ga, Sn et Sb) possèdent d'intéressantes propriétés mécaniques, magnétiques et thermiques qui découlent de la transition structurale martensite-austénite. Le couplage de ces propriétés entraîne de potentielles applications dans le domaine des actionneurs, des capteurs ou des refroidisseurs. La fabrication de ces matériaux en films, d'un grand intérêt pour les microsystèmes, reste difficile à maitriser et fait l'objet de ce travail de thèse. Une partie du travail effectué durant cette thèse porte donc sur l'élaboration d'un film de type Ni-Co-Mn-In en utilisant un procédé de co-pulvérisation. L'objectif de la thèse a porté sur l'obtention d'un film présentant une transition structurale et magnétique à température ambiante. Après une étude de la structure et de la microstructure des phases martensite et austénite, les propriétés magnétiques ont été investiguées. Le changement d'état magnétique obtenu pour certains films lors de la transition du premier ordre a entrainé des propriétés magnétocaloriques et d'actionnement intéressantes. Les meilleurs résultats sont obtenus pour un film de composition Ni45,2Co4,7Mn36,2In13,9. La réalisation de mesures de résistivité sous champ magnétique intense constitue un sujet novateur sur des films de ce type. Grâce à ces mesures, une étude de l'irréversibilité et du blocage de la transformation structurale induit par le champ magnétique (kinetic arrest) a été réalisée. La compréhension des phénomènes intervenant dans l'hystérésis thermique et le blocage sous champ magnétique est en effet importante pour les applications basées sur ces matériaux à fort couplage mécanique, magnétique et thermique. / Ni-Mn-X (X=In, Ga, Sn and Sb) Heusler type alloys present interesting mechanical, magnetical and thermal properties owing to the martensite-austenite structural transition. Combining these properties induce many potentials applications in the field of actuators, sensors and coolers. Processing these materials into films is of great interest for micro-devices but remains a challenge. It shall be the purpose of this thesis. Part of this thesis shall be dedicated to the development of a Ni-Co-Mn-In Heusler film using a co-sputtering process. The main achievement of the thesis is to have obtained a film exhibiting a structural and magnetic transformation at room temperature. After a study of the structure and microstructure of martensite and austenite phases, magnetic properties are investigated. The evolution of the magnetic state during the first order transformation observed in some films leads to interesting magnetocaloric and activating properties. Optimal results, both in terms of working temperature and functional properties, are obtained for a film with a composition of Ni45,2Co4,7Mn36,2In13,9. Resistivity measurements under high magnetic field are novel on such films. These new measurements have made it possible to study the irreversibility and phase transformation blocking induced by a magnetic field (kinetic arrest). Understanding the physical effect underlying the thermal irreversibility and the blocking by a magnetic field is indeed important for applications based on such materials with strongly coupled mechanical, magnetical and thermal properties.

Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.