Graphene-Enhanced Magnetic Anisotropies in Fe/Ni (100) Superlattices with Monolayer Periodicity

Fe/Ni(100) superlattices grown on graphene/Ir(100) by intercalation of alternate monolayers of Ni and Fe under graphene show magnetic properties severely modified. The graphene–iron interaction at the external interface produces a surface anisotropy Kint(gr/Fe) = 0.89 ± 0.08 mJ/m2, large enough to drive the uniaxial, out-of-plane magnetic anisotropy of the whole superlattice to KU = 0.87 ± 0.03 MJ/m3 and compensate the in-plane shape anisotropy characteristic of thin magnetic layers. Graphene also introduces an additional trigonal in-plane anisotropy superimposed to the biaxial anisotropy of the underlying Fe/Ni (100) superlattice and increases the mL(parallel)/mspin ratio by 50% with respect to Fe/Ni films grown without graphene, as determined by XMCD. The films show chemical ordering plane-by-plane and a strongly distorted face-centered tetragonal (fct) structure, as determined by synchrotron-based X-ray diffraction. The gr-Fe charge transfer and the electronic hybridization of the respective π and d bands at the interface are responsible for the observed magnetic phenomena.