We present a new route of tethering graphene nanoplatelets (GNPs) with Fe3O4 nanoparticles to enable their alignment in an epoxy using a weak magnetic field. The GNPs are first stabilized in water using polyvinylpyrrolidone (PVP) and Fe3O4 nanoparticles are then attached via co-precipitation. The resultant Fe3O4/PVP-GNPs nanohybrids are superparamagnetic and can be aligned in an epoxy resin, before gelation, by applying a weak magnetic field as low as 0.009 T. A theoretical model describing the alignment process is presented and used to quantify the effects of key parameters on the time needed for the alignment process. Compared to the unmodified epoxy, the resulting epoxy polymer nanocomposites containing randomly-oriented Fe3O4/PVP-GNPs nanohybrids exhibit significantly improved electrical conductivities by up to three orders of magnitude and fracture energies by up to 300%. The alignment of the Fe3O4/PVP-GNPs nanohybrids in the epoxy polymer nanocomposites transverse to the direction of crack propagation further increased the fracture energy by 50%, and the electrical conductivity by seven fold in the alignment direction, compared to the nanocomposites containing randomly-oriented nanohybrids. (C) 2016 Elsevier Ltd. All rights reserved.