Layered CrGe₁-_xSe_{3 y} with Cr kagome lattice and antiferromagnetic ordering

We report the synthesis and properties of a new layered material, CrGe1−xSe3+y. The crystal structure was determined by using single crystal x-ray diffraction and transmission electron microscopy. CrGe1−xSe3+y crystallizes with a space group R−3m, featuring a double kagome layer of chromium atoms, sandwiched between disordered Ge-Se layers. This compound displays antiferromagnetic order below 50 K, unlike the ferromagnetic behavior in CrGeTe3. Chromium displays an effective moment of ∼3.9μB/Cr, consistent with Cr3+ oxidation. The presence of this phase limits the possibility of a ferromagnetic CrGeSe3 analogous to CrGeTe3.