Strong ferromagnetic coupling and tunable easy magnetization directions of FexCo1−x layer(s) intercalated under graphene

We report the magnetic response of FexCo1−x layer(s) intercalated under graphene, compared with the bulk equiatomic FeCo(1 0 0) specimen. Graphene grown on Ir(1 1 1) can act as a protective membrane, allowing confined epitaxial growth of homogeneous FexCo1−x layer(s). Few intercalated FexCo1−x layers exhibit a significant enhancement of the spin (Seff) and orbital (L) moments with respect to both the single elements and the bulk equiatomic FeCo(1 0 0) configuration, as demonstrated by means of magnetic circular dichroism experiments. Reducing the intercalant thickness down to a single layer of FexCo1−x, the easy magnetization direction switches from parallel to perpendicular to the surface plane, with a magnetic response being influenced by the underlying metal. Element-sensitive hysteresis loops disclose identical magnetization response at the Fe and Co sites, thus constituting a single magnetic unit with enhanced ferromagnetic response, with Fe acting as a strong ferromagnet, differently from its bulk bcc configuration. This is a significant step towards the control at the atomic scale of the magnetic response in low dimensional 3d transition metal alloys, with tunable easy-magnetization direction, enhanced spin moments and magnetic anisotropy, in a inert and protected configuration thanks to the 2D graphene cover.