Alignment of polymer based magnetic composites in magnetic field

•The magnetic field applied to samples during film formation strongly affects morphology and electric properties of films.•GNP covered with magnetite nanoparticles tend to align along the magnetic field and form more porous structure.•Thin films formed without (with) magnetic field have activation character of conductivity (of metallic conductivity).•Possible mechanisms of the above transformations in forming films without and with magnetic field are discussed. Composite films made of graphene nanoplatelets (GNP) and magnetite Fe3O4 nanoparticles have been prepared with and without magnetic field. Poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) was used as a stabilizing polymer matrix. Film morphology was found to depend strongly on the presence of magnetic field, i.e. more porous structure of GNP- Fe3O4 is formed in magnetic field. Thin films formed without magnetic field have activation character of conductivity, while thin films formed in magnetic field have metallic conductivity. Thus, the magnetic field acting during film formation in these composites results in semiconductor-metal transition. DFT calculations show that at low distance between GNP surface and nanoparticle strong interaction between them can be observed.