Nanoparticles are one of our interests, as an individual entity or as the basic units of bulk and complex nanomaterials. We are developing new methods for the controlled synthesis of nanoparticles and coupling strategies for the synthesis of hybrid materials and nanocomposites. For this purpose, we focus on the design of nanoparticles’ surface chemistries, which determine their properties and applications. We also study the effect of the final size of nanoparticles on their chemical (structure, stability, catalysis) and physical (magnetic, electric, optic, rheological) properties.
Anisotropic magnetic nanoparticles can mediate a magnetic-to-mechanical energy transfer under a low-frequency magnetic field. The effect is useful in technical areas (e.g., stirring) and medicine (magneto-mechanical cancer treatment), while magnetic nanoplatelets are the basic constituents of ferromagnetic fluids and, currently, the only existing liquid magnets. The shape of the nanoparticles can be controlled by the synthesis route. We study particle-growth mechanisms and their effects on the nanoparticles’ shapes, and the assembly of isotropic nanoparticles into anisotropic structures.
Multifunctional materials combine the different functional properties of the constituent materials. The basic ingredients are various types of nanoparticles that are physically or chemically coupled. Examples are magnetic catalysts, and magneto-optic and magneto-electric composites. Nanoparticles are incorporated into various bulk matrices through a careful design of their surface chemistry to make magneto-optic polymers and ferromagnetic liquid crystals. An alternative approach is the synthesis of core-shell nanoparticles, for example, exchange-coupled bi-magnetic nanoparticles, and the synthesis of Janus nanoparticles.
Magnetic materials for micro- and mm-waves
Magnetic materials for micro- and mm-waves suitable for the absorbers of electromagnetic waves and for non-reciprocal ferrite devices are being developed. These studies involve synthesis, the chemistry of materials, and the characterization and correlation of the chemical and physical properties of materials. Ceramics and composites based on ferrites are studied for microwave applications, and a new method for the preparation of magnetically oriented thick hexaferrite films is under development for mm-wave applications.
Mastering the composition and properties of grain boundaries in certain semiconducting ceramics (ZnO, BaTiO3) allows us to prepare materials with an electrical resistivity that is voltage dependent (varistors) or temperature dependent (resistors with PTCR = posistors). We are developing lead-free high-temperature PTCR resistors. As an alternative to the classic PTCR materials based on BaTiO3, we are developing new PTCR materials, i.e., composites of an insulating ferroelectric phase in a conductive matrix. These new materials are distinguished by a significant jump in the electrical resistivity at the operating temperature.