Miran Baričić will defend his Phd thesis entitled : ” Tailoring Magnetic Interactions in Nanostructured Oxides: Polyol Synthesis and Interfacial Design of CoO-Based Systems ” on Tuesday 08/04/2025, 2:00 PM at Amphi Turing, bâtiment Sophie Germain RDC – Campus des Grands Moulins – Université Paris Cité.
Résumé :
Nanostructured materials often display physical properties that differ profoundly from their bulk counterparts, largely due to enhanced surface effects and quantum confinement at the nanoscale. This thesis investigates
how these features can be leveraged to control magnetic behavior in metal oxide nanoparticles, focusing on cobalt(II) oxide (CoO), a model antiferromagnet with strong magnetic anisotropy and structural simplicity.
A major part of this work is devoted to optimizing the polyol synthesis of CoO, a wet-chemical method that, despite its versatility, had remained poorly explored in terms of reaction control. By replacing conventional
diethylene glycol with longer-chain polyols such as tetraethylene glycol, it was possible to push the reaction temperature higher, enabling superior control over crystallite size, morphology, and phase purity. Magnetic
characterization revealed a size-dependent shift in the Néel temperature, and even uncovered the presence of minor magnetic impurities undetectable by structural probes.
To unravel the formation mechanisms of CoO and cobalt ferrite (CoFe2O4), time-resolved synchrotron X-ray diffraction and SAXS were employed. These in situ techniques exposed the early stages of nucleation,
revealing the presence of pre-nucleation clusters and a stepwise growth process. A comparative analysis
highlighted key differences in the reaction pathways of CoO and CoFe2O4, contributing to a deeper understanding of polyol-based nanoparticle formation.
Finally, the magnetic coupling between CoO and nickel ferrite (NiFe2O4) was explored through the design of core-satellite nanocomposites. Thanks to the reduced magnetic anisotropy mismatch between these two
materials, significant exchange bias effects and enhanced coercivity were observed, outperforming previously reported CoFe2O4–CoO systems.
Altogether, this work demonstrates how synthetic control and interfacial engineering can be used to tailor the magnetic properties of oxide nanomaterials, offering new insights into nanomagnetism and expanding the design strategies for future applications in data storage, spintronics, and magnetic sensing.