Advancing Room-Temperature Magnetic Semiconductors with Organic Radical Charge Transfer Cocrystals.

Developing purely organic room-temperature magnetic semiconductors has been a long-sought goal in the material community toward the simultaneous control of spin and charge. Organic cocrystals, known for their structural versatility and multifunctionality, are ideal candidates for these magnetoelectric coupling applications. However, organic room-temperature magnetic semiconductor cocrystals have rarely been reported, and their mechanisms remain poorly understood due to the complexity of cocrystal structures. Here, doping organic cocrystals with radicals offers a promising strategy for boosting their magnetism and conductivity while maintaining their cocrystal structures. The fluoranthene-7,7,8,8-tetracyanoquinodimethane radical (FA-HTCNQ•) is constructed through a simple, rapid, and eco-friendly solution-processing approach. The conductive FA-HTCNQ• exhibits excellent room-temperature ferromagnetism with the coercive fields of 96 Oe and the Curie temperature near 400 K, superior to its structural-identical undoped counterpart. Meanwhile, the room-temperature magnetoelectric coupling is demonstrated in the conductive FA-HTCNQ•. The stronger ferromagnetism and conductivity in organic cocrystals are attributed to the enhanced charge-transfer (CT) interactions induced by radicals, rather than the spin exchange interactions between these radicals alone. The research manifests the origin of ferromagnetism in organic cocrystals and provides a simple strategy to fabricate pure organic room-temperature magnetic semiconductor materials for future integrated magnetoelectric devices.