Magnetic-field-orientation-controlled spin-dependent charge transport in organic magnetic transistors

Organic magnetic semiconductors have attracted considerable attention because of their potential applications in flexible spintronic devices. Although magnetic nanoparticles (NPs) have been widely incorporated into organic semiconductors to improve device performance, the relationship between interfacial magnetic interactions and charge transport is still not fully understood. In this work, superparamagnetic Fe3O4 NPs were incorporated into the high-mobility conjugated polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) to fabricate magnetic organic field-effect transistors (MOFETs) with Ni source and drain electrodes. The incorporation of Fe3O4 NPs modified the molecular packing of PBTTT-C14 and introduced magnetic characteristics into the polymer films through interfacial interactions. The resulting MOFETs exhibited a clear dependence on applied magnetic-field orientation. Among the three magnetic-field directions investigated, the magnetic field applied parallel to the carrier transport direction produced the largest threshold-voltage shift, drain-current enhancement, and magnetoresistance. Time-resolved photoluminescence, electron paramagnetic resonance, contact resistance, and electrical measurements further revealed that the applied magnetic field reduced spin-dependent carrier scattering by aligning the magnetic moments of Fe3O4 NPs, leading to improved carrier injection and transport. These results clarify the role of magnetic-field orientation in regulating charge transport through interfacial magnetic interactions and provide useful insights into the design of organic magnetic semiconductors for flexible spintronic and magnetic sensing applications.