Cubic Mesocrystal Magnetic Iron Oxide Nanoparticle Formation by Oriented Aggregation of Cubes in Organic Media: A Rational Design to Enhance the Magnetic Hyperthermia Efficiency

Magnetic iron oxidemesocrystals have been reported toexhibitcollective magnetic properties and consequently enhanced heating capabilitiesunder alternating magnetic fields. However, there is no universalmechanism to fully explain the formation pathway that determines theparticle diameter, crystal size, and shape of these mesocrystals andtheir evolution along with the reaction. In this work, we have analyzedthe formation of cubic magnetic iron oxide mesocrystals by thermaldecomposition in organic media. We have observed that a nonclassicalpathway leads to mesocrystals via the attachment of crystallographicallyaligned primary cubic particles and grows through sintering with timeto achieve a sizable single crystal. In this case, the solvent 1-octadeceneand the surfactant agent biphenyl-4-carboxylic acid seem to be thekey parameters to form cubic mesocrystals as intermediates of thereaction in the presence of oleic acid. Interestingly, the magneticproperties and hyperthermia efficiency of the aqueous suspensionsstrongly depend on the degree of aggregation of the cores formingthe final particle. The highest saturation magnetization and specificabsorption rate values were found for the less aggregated mesocrystals.Thus, these cubic magnetic iron oxide mesocrystals stand out as anexcellent alternative for biomedical applications with their enhancedmagnetic properties.

Automated summary

This work analyzes the formation mechanism of cubic magnetic iron oxide mesocrystals by thermal decomposition in organic media, finding a nonclassical pathway via the attachment of crystallographically aligned primary cubic particles and sintering to achieve a sizable single crystal. The solvent 1-octadecene and the surfactant agent biphenyl-4-carboxylic acid are key parameters. The degree of aggregation of the cores forming the final particle strongly affects the magnetic properties and hyperthermia efficiency.