Toward nanoscale multiferroic devices: Magnetic field-directed self-assembly and chaining in Janus nanofibers

Optical microscopy is used to observe magnetic field driven chaining of Janus nanofibers electrospun from CoFe2O4 and BaTiO3 sol-gel precursors. Chaining as a function of applied field strength follows the expected power law for diffusion limited chaining at low concentrations. At higher concentrations chain length increases rapidly at low fields but more slowly at higher fields, with a transition at 100 Oe. This change in dynamics means field-dependent scaling exponents, suggesting mass-dependent chaining for low fields and diffusion limited chaining for higher fields. The angular dispersion of the chains relative to the external field direction also shows a transition near 100 Oe, decreasing monotonically at higher fields. These results suggest that assembly models developed for nanoparticles need to be modified to properly describe assembly in nanorods and nanofibers.