Ho‐Ion‐Polymer/Graphene Heterojunctions Toward Room‐Temperature Ferromagnets

Abstract Organic ferromagnetic materials offer great promise for spintronic devices, carbon‐based chips, and quantum communications, but remain as a challenging issue due to their low saturation magnetization and/or unsustainable ferromagnetic properties. To date, magnetic ion polymers have displayed paramagnetism without exception at room‐temperature. In this study, it is reported for the first time that, owing to the structural restriction and charge exchange of Ho ion by polymer/graphene π–π stacking heterojunctions, holmium ion polymer composites exhibited typical hysteresis lines of ferromagnetic materials at room temperature. The room‐temperature ferromagnetic ion polymer composite presented the highest saturation magnetization value of 3.36 emu g⁻¹ and unprecedented sustainable ferromagnetism, compared to reported room‐temperature organic ferromagnetic materials. Accordingly, prepared ferromagnetic composites also achieved impressive wave absorption properties, with a maximum reflection loss of as much as −57.32 dB and a broad absorption bandwidth of 5.05 GHz. These findings may promote the development of room‐temperature organic ferromagnetic materials.