Iron-based magnetic nanoparticles by spark ablation

Magnetic nanoparticles have shown great potential for use in drug delivery and bioimaging applications and are prospective building blocks in future high-performing permanent magnets. Today, magnetic nanoparticles are most often produced in batches by chemical methods resulting in the risk of chemical impurities and production of vast amounts of chemical waste. Aerosol generation methods on the other hand, particularly spark ablation, are promising for future generation of magnetic nanoparticles since they are simple, fast, continuous, scalable, provide good control of size and composition, and offer the possibility to form alloys of material combinations not miscible on the macroscopic scale. High controllability is of utmost importance when generating magnetic nanoparticles since small deviations in size can significantly alter the magnetic coercivity. Also, the composition of the particles is of high significance since the magnetic properties can be completely transformed by changes in elemental composition or the oxidation state of the particle.
In this work, we present the successful generation of monodisperse bimetallic FeCr and FeMn nanoparticles by spark ablation, and the results from the thorough characterization of individual particles with aerosol instruments, transmission electron microscopy, and synchrotron-based X-ray photoelectron spectroscopy. We demonstrate how the carrier gas can be used to dictate the oxidation and how to alternate between self-passivated and completely oxidized nanoparticles. We also show how the produced particles can be deposited to yield a low surface concentration which is critical for minimizing interparticle interactions during magnetic measurements. Finally, as a proof of concept, measurements using a magnetometer equipped with a SQUID on samples with different particle coverages are presented.