▎ 摘　　要

Activating ferromagnetic couplings of transition-metallic ions in the antiferromagnetic metal oxide semiconductors is desired for creating ferromagnetic semiconductors for spintronics applications. Here, we report intrinsic ferromagnetic coupling in a typical antiferromagnetic metal oxide Co3O4, by virtue of a hybrid structure that modifies the valence state of Co ions. The Co3O4 quantum dots exhibit ferromagnetism of 2.2 emu/g at 2K after hybridization with reduced graphene oxide (RGO). In this hybrid structure, electron-transfer from RGO to Co3O4 occurs and Co3+ ions occupying the octahedral (O-h) positions are converted into Co2+. Then the super-exchange interactions between Co2+ ions at T-d (tetrahedral) and O-h positions switch the magnetic coupling of Co2+(T-d)-Co2+(T-d) from antiferromagnetic to ferromagnetic. These results offer promise for tailoring the spin exchange interactions of oxide semiconductors for spintronics applications. Published by AIP Publishing.