▎ 摘　　要

The combination of exchange spring magnets with graphene sheets is expected to be an effective method for preparing an ultrathin electromagnetic wave absorber. However, the synthesis of such a composite is still a challenge and has not yet been explored. Herein, a layered double hydroxide (LDH) array is used for the first time as a precursor for an exchange spring magnet. By controllable annealing of CoFe LDH array/graphene oxide precursors in an NH3 atmosphere, we synthesize CoFe alloy/nitrides/N-doped graphene composites. The magnetic exchange coupling between soft magnetic phases (Co7Fe3, Co5.47N) and the hard magnetic phase (Fe3N) improves the magnetic loss in the high-frequency region. Moreover, the heterogeneous interfaces between multiple phases generate strong interfacial polarization loss, and the N incorporation in graphene causes large conductive loss and dipole polarization loss. The composite exhibits an extremely strong electromagnetic wave absorption performance with a reflection loss of -59.1 dB at an ultrathin layer thickness of 1.4 mm. Remarkably, its specific reflection loss value (reflection loss/thickness) achieves a new record among all the magnetic nanomaterial-graphene composite absorbers, which implies its potential application as an excellent ultrathin EMW absorbing layer. This study provides a new method to prepare an exchange spring magnet and highlights the importance of magnetic exchange coupling in improving electromagnetic wave absorption.