Lanthanide f7 metalloxenes - a class of intrinsic 2D ferromagnets

As the thickness of layered compounds approaches the monolayer limit, new electronic states and properties emerge. The sheer range of such properties is astounding but the list did not include intrinsic magnetism. Until recently. At the moment, several compounds do reveal intrinsic ferromagnetism at the 2D limit. However, they seem to be chemically and structurally unrelated, which is not conducive to a systematic search of new 2D magnets. Here, we demonstrate that lanthanide metalloxenes form a class of intrinsic 2D ferromagnets. Their stoichiometric layered structure LnX(2) is composed of a triangular lattice of lanthanide ions (Eu or Gd) coupled with a 2D Xene sheet, a honeycomb network formed by Si or Ge. The materials are synthesized by direct reaction between the elements, with varying thickness from the bulk down to 1 monolayer. The common pattern is transformation from 3D antiferromagnetism to 2D ferromagnetism as revealed by magnetization and electron transport measurements. This work sets a path for a rational synthesis of 2D magnets and study of their spin behaviors for spintronic applications.