In situ powder X-ray diffraction study of magnetic CoFe2O4 nanocrystallite synthesis.

The evolution of size and size distribution during hydrothermal synthesis of nanocrystalline CoFe2O4 has been studied by in situ synchrotron powder X-ray diffraction (PXRD). Varying synthesis temperature or [OH(-)] concentration in the precursor proves to have no significant effect on the final volume-weighted nanocrystallite sizes (∼12 nm) of CoFe2O4. However, analysis by whole powder pattern modeling of the [OH(-)] concentration series reveals a substantial difference in the number-weighted size distributions when varying the amount of base used. Furthermore, changing the metal ion concentration prior to NaOH addition in the precursor preparation gives a handle to control the nanoparticle sizes (∼5-15 nm). All in situ experiments show almost instantaneous formation of the CoFe2O4 nanocrystallites, without significant growth or broadening of the size distribution after 60 s. Magnetic hysteresis curve measurements illustrate, how this facilitates the tailoring of materials with specific magnetic properties, as larger particles (∼15 nm) exhibit hard magnetic properties while the smaller particles (∼6-7 nm) are superparamagnetic.