Pyrene-Enhanced Ferromagnetic Interaction in a FeCl4–-Based Poly(ionic liquid)s Organic Magnet

Organic magnets are promising in quantum computers, spintronic devices, and information storages for their excellent processing and smart design abilities, resulting from the organic part. However, the organic part shields the magnetic centers to weaken the magnetic interaction. In this work, π–π stacking planar pyrene groups are introduced into cations of a magnetic ionic liquid (NBPBI[FeCl4]) and poly(ionic liquid) (PNBPBI[FeCl4]) with FeCl4– as the anions. By introducing pyrene groups, the shortest distance between neighboring magnetic units is within 4 Å. The ferromagnetic interactions in NBPBI[FeCl4] and PNBPBI[FeCl4] are enhanced by the π–π stacking pyrene groups. Moreover, the corresponding organic magnets are soft ferromagnets, as phase transition from paramagnetism to ferromagnetism is observed from zero field cooling and field cooling tests at the low temperature. This is a new strategy for designing a ferromagnetic organic magnet.