EurOgels: A Ferromagnetic Semiconductor with Porous Structure Prepared via the Assembly of Hybrid Nanorods

Bastian Trepka, Julian Stiegeler, Ilona Wimmer, Mikhail Fonin and Sebastian Polarz Nanoscale DOI: 10.1039/C8NR06536E

EuO is unique, because it belongs to the few solids combining semiconducting properties (Egap = 1.1 eV) with native ferromagnetism. For future applications of EuO, e.g. as spin-filters or for sensors, one has to learn, how defined nanostructures can be prepared. Unlike to other ceramic oxides, there are no established soft-chemistry routes (e.g. sol-gel) towards EuO nanomaterials e.g. porous materials. This is due to the labile nature of the oxidation state Eu(+II). We present a particle-based method leading to an EuO aerogel. Instead of making the target material directly, we use nanoparticles of an organic-inorganic hybrid phase (Eu2O3-benzoate), assemble those into an aerogel, followed by the transformation into phase-pure EuO. It is shown organic aldehydes function act as capping agents for controlling the morphogenesis of the hybrid particles. Depending on steric demand of the aldehyde one obtains plate-like particles or nanorods with increasing aspect ratio. The particles form a gel, when the aspect ratio is increased to >20. After supercritical drying one receives a nanorod-based aerogel. Treatment of the latter with Eu-vapor leads to reduction of the Eu2O3 domains to EuO while retaining the aerogel structure. Proof of ferromagnetism in the resulting EuO aerogel was delivered by SQUID measurements.