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.
We report magnetic properties of electrospun multiferroic nanofibers assembled into linear aggregates with an external magnetic field, and measured with the magneto-optical Kerr effect (MOKE) in a non-specular or scattering geometry (ScMOKE). Compared with bulk magnetometry, ScMOKE’s sensitivity to subtle differences between aggregates offers a route to determine local multiferroic coupling in disordered nanomaterials. CoFe2O4-BaTiO3 nanofiber agglomerates are assembled prior to measurement by suspending and aligning the fibers in a transparent air-cured polyvinyl alcohol solution. We detect the polarization change in light scattered from the fibers, collected at an off-specular angle in order to eliminate the background caused by substrate reflection. Averaged hysteresis loops from different agglomerates show a variety of unique structures. For our optical spot size of ∼15 m, multiple fibers, within a single agglomerate, are detected simultaneously, suggesting ScMOKE can distinguish local magnetization reversal fields that vary from fiber to fiber, as well as magnetic interactions between fibers.
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