Facile synthesis of magnetic nanoparticles optimized towards high heating rates upon magnetic induction

Inductively heatable magnetic particles are powerful additives towards smart processes, such as bonding and debonding on demand or self-healing. For the best efficiency, particles are needed which possess the highest possible heating rates/specific absorption rate when being exposed to a magnetic induction field. Herein, a cheap, simple and upscalable precipitation-oxidation assisted aging synthesis route for magnetic nanoparticles is optimized towards yielding a product with high heating rates. In-depth synthesis parameter studies were carried out to understand how the nanoparticle structure can be influenced in a way to yield the best heating rates. This included variation of the precursors chemistries, precipitant concentration, the oxidation and aging conditions as well as the co-doping of the particles with Zn and Co. A correlation between magnetic hysteresis, measured via vibrating sample magnetometry and specific absorption rate of the samples was established and it was demonstrated how crucial it is to select the right range of external magnetic fields in hysteresis measurements in order to achieve reliable and predictable correlations with the specific absorption power and heating rates, respectively. Via the established understanding and the systematic variation, it was ultimately possible to develop a synthesis procedure, yielding ferrimagnetic iron oxide nanoparticles that come with specific absorption rates of up to 1474 W·g−1 (at a magnetic field of 430 Oe at 1013 kHz).