Structural and Magnetic Properties of Sputtered Chromium-Doped Sb2Te3 Thin Films

Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb2Te3. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XAS/XMCD) techniques to study the structure and magnetism of Cr-doped Sb2Te3 films. Symmetric θ-2θ XRD and RSM establish a solubility window. Layered tetradymite order persists up to ∼10 at.-% Cr, while higher doping yields CrTe/Cr2Te3 secondary phases. STEM reveals nanocrystalline layered stacking at low Cr and loss of long-range layering at higher Cr concentrations, consistent with XRD/RSM. Magnetometry on a 6% film shows soft ferromagnetism at 5 K. XAS and XMCD at the Cr L2,3 edges exhibits a depth dependence: total electron yield (TE; surface sensitive) shows both nominal Cr2+ and Cr3+, whereas fluorescence yield (FY; bulk sensitive) shows a much higher Cr2+ weight. Sum rules applied to TEY give mL=(0.20±0.04) μB/Cr, and mS=(1.6±0.2) μB/Cr, whereby we note that the applied maximum field (3 T) likely underestimates mS. These results define a practical growth window and outline key parameters for MTI films.