Observation of room-temperature ferromagnetism in copper-based graphene induced by stress engineering

Two-dimensional (2D) room-temperature ferromagnetism is highly sought after for its great application potential but is challenged by chemical or magnetic structural instability. If room-temperature ferromagnetism can be realized in structurally stable 2D graphene, it will have a broad application prospect and market in flexible spintronics and wearable artificial intelligence. Although symmetry breaking such as vacancies, edges can introduce localized magnetic moments in intrinsically antimagnetic graphene, their weak coupling can only hold long-range ordering at low temperatures. Here, a robust ferromagnetic order has been observed in large-area graphene (centimeter scale) through mechanical folding and successive preprocesses of rapid cooling and heating method, where the Curie temperature of ∼6-layer graphene is close to 100 K and that of ∼10-layer graphene is above room temperature. We propose that the observed ferromagnetism is possibly attributed to the surface sp3-type bonds emergent in the structure phase transition caused by strain effects. Intrinsic graphene cannot hold ferromagnetic order, although that is highly desired. In this work, a transition from paramagnetism to ferromagnetism is observed in copper-based graphene after mechanical folding with successive rapid cooling and heating process. Stress engineering in the wrinkled graphene is possible to promote the formation of sp3-type bonds, which support the robust ferromagnetic order. [Display omitted] •A breakthrough in ferromagnetic 2-dimensional material for future flexible spintronics and artificial intelligence.•Overcoming the diamagnetism limitation of graphene, one of the most promising van der Waals materials.•A simple and effective method to introduce robust ferromagnetism in large area graphene.•Unveiling the crucial role of sp2 to sp3 C–C phase transition in maintaining graphene's robust ferromagnetic order.