A layered double hydroxide-derived exchange spring magnet array grown on graphene and its application as an ultrathin electromagnetic wave absorbing material

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.