Tailoring Exchange Coupling in Carbon-Based Magnetic Materials

In this paper, geometric structure, electronic structure, and magnetic properties of several radicals, that is,
${\rm C}_{13}{\rm H}_{9}$
,
${\rm C}_{13}{\rm F}_{9}$
, and
${\rm C}_{13}{\rm Cl}_{9}$
have been investigated based on density-functional theory with dispersion correction. Each of these radicals has a spin of 1/2. However, in their dimer structures, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid the typical antiferromagnetic spin-exchange of identical face-to-face radicals, alternating stacks of
$\pi$
-radicals and diamagnetic molecules have been designed. Our calculated results confirm that alternating stacks have ferromagnetic spin-exchange between radicals. To explore a way to tailor exchange coupling in carbon-based magnetic materials, the effect of size of diamagnetic molecules on spin-exchange coupling in stacks has been investigated. Moreover, the nature of spin-exchange coupling in stacks is shed light on. These results demonstrate an effective way to tailor exchange coupling in carbon-based materials.