  We report laser-assisted photochemical graphitization of polyimides (PI) into
functional magnetic nanocomposites using laser irradiation of PI in the
presence of magnetite nanoparticles (MNP). PI Kapton sheets covered with MNP
were photochemically treated under ambient conditions using a picosecond pulsed
laser (1064nm) to obtain an electrically conductive material. Scanning electron
microscopy of the treated material revealed layered magnetic
nanoparticles/graphite nanocomposite structure (MNP/graphite). Four probe
conductivity measurements indicated that nanocomposite has an electrical
conductivity of 1550 S/m. Superconducting quantum interference device (SQUID)
magnetometer-based magnetic characterization of the treated material revealed
an anisotropic ferromagnetic response in the MNP/graphite nanocomposite
compared to the isotropic response of MNP. Raman spectroscopy of MNP/graphite
nanocomposite revealed a four-fold improvement in graphitization, suppression
in disorder, and decreased nitrogenous impurities compared to the graphitic
material obtained from laser treatment of just PI sheets. X-ray photoelectron
spectroscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy were
used to delineate the phase transformations of MNP during the formation of
MNP/graphite nanocomposite. Post-mortem characterization indicates a possible
photocatalytic effect of MNP during MNP/graphite nanocomposite formation. Under
laser irradiation, MNP transformed from the initial Fe3O4 phase to
{\gamma}-Fe2O3 and Fe5C2 phases and acted as nucleation spots to catalyze the
graphitization process of PI.
