We theoretically design a graphene-based all-organic ferromagnetic semiconductor by terminating zigzag graphene nanoribbons (ZGNRs) with organic magnets. A large spin-split gap with 100% spin polarized density of states near the Fermi energy is obtained, which is of potential application in spin transistors. The interplays among electron, spin and lattice degrees of freedom are studied using the first-principles calculations combined with fundamental model analysis. All of the calculations consistently demonstrate that although no d electrons existing, the antiferromagnetic pi-pi exchange together with the strong spin-lattice interactions between organic magnets and ZGNRs make the ground state ferromagnetic. The fundamental physics makes it possible to optimally select the organic magnets towards practical applications.
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