▎ 摘　　要

We investigate the spin- polarized transport properties of relativistic electrons tunnelling through a fractal graphene superlattice (FGSL) sandwiched between two ferromagnetic graphene (FG) electrodes, where the FGSL can be regarded as a symmetric periodic graphene superlattice (SPGSL) with defects. The spin conductance and the tunnelling magnetoresistance of the FG/FGSL/FG junction are numerically calculated and compared with those of the FG/SPGSL/FG junction. We find that the spin conductance and the tunnelling magnetoresistance reach a minimum value in the vicinity of the new Dirac point and can be greatly modulated not only by the Fermi energy and the exchange splitting energy, but also by the structural configuration. Compared to those of the FG/SPGSL/FG junction, the spin conductance and the tunnelling magnetoresistance of the FG/FGSL/FG junction can exhibit a stronger and more irregular oscillation with increasing Fermi energy, along with typical high- frequency quasiperiodic oscillations as the barrier height increases. We also find that the maximum value of the tunnelling magnetoresistance is robust against change of the lattice parameters and the profile of the graphene superlattice, but dependent on the Fermi energy and the exchange splitting energy.