Organic Ferromagnetism: Trapping Spins in the Glassy State of an Organic Network Structure

The unique organic π-conjugated network structure was synthesized in trifluoromethanesulfonic acid at 155°C by self-polymerization of the tetracyanoquinodimethane (TCNQ) monomer in an efficient way. Highly stable free radicals achieved through the self-polymerization of TCNQ, these radicals originate from the 90° rotation of cyclohexadiene rings into phenyl rings and 120° ferromagnetic order around the triazine rings. The presence of unpaired electrons (radicals) in p-TCNQ was established by solid-state electron spin resonance spectroscopy, and the long-range magnetic ordering through the network was characterized by a Quantum Design SQUID-VSM. Designing and manipulating the spins in polymer networks via organic methodologies will provide alternative approaches for versatile future applications of plastic magnets. For over two decades, there has been widespread skepticism around claims of organic plastic ferromagnetism, mostly as a result of contamination by transition metals. Excluding the contamination issues and realizing magnetic properties from pure organic plastics must occur to revive the quest for plastic magnetism. Here, we report the design, synthesis, and magnetic properties of a triazine network polymer demonstrating room-temperature ferromagnetism derived from pure organic single crystals. The polymer network was realized through the self-polymerization of tetracyanoquinodimethane (TCNQ). We generated highly stable free radicals by twisting π bonds around the triazine rings and by trapping them in the glassy state of a polymerized TCNQ (p-TCNQ) network structure. Magnetic characterization revealed the presence of spin-½ moments, which led to ferromagnetic ordering with a critical temperature significantly higher than room temperature. Polymerized TCNQ was evaluated as a metal-free ferromagnetically active organic material and showed unusual ferromagnetic properties. This study provides insights to guide the design and development of materials for future organic flexible magnetic materials.