Two-dimensional ferromagnetism in Eu-intercalated few-layer graphene

•A europium lattice between graphene monolayers forms a van der Waals compound.•Europium-intercalated few-layer graphene exhibits two-dimensional ferromagnetism.•The material makes a ready-to-use element for van der Waals heterostructures.•The results expand the family of 2D magnets. 2D magnets hold high promise for unconventional quantum phases, exploration of fundamental physics of magnetism, ultra-compact devices based on van der Waals heterostructures. Graphene is a constant inspiration for design of 2D materials; stoichiometric graphene-based compounds with magnetic atoms give rise to 2D ferromagnets. Unfortunately, addition of magnetic species induces high chemical reactivity. Here, we encapsulate a monolayer Eu lattice between graphene monolayers to form a chemically inert van der Waals 2D ferromagnet. The material is produced by Eu intercalation into few-layer graphene, as confirmed by a combination of diffraction and microscopy techniques. The emergence of ferromagnetism is witnessed by magnetization and electron transport measurements. The effective Curie temperature is controlled by weak magnetic fields manifesting the 2D nature of the magnetic state. The results expand the family of 2D magnets and establish a versatile platform for synthesis of its new members by metal intercalation.