Defect Induced Unconventional Ferromagnetism in Au Intercalated Bi₂Se₃ Nanocrystals for Spintronic Applications

Abstract

Breaking time‐reversal symmetry through magnetic impurities has been a useful strategy for achieving exotic physical phenomena in topological insulators for a long time. In contrast, reports on achieving ferromagnetism in topological insulators by introducing non‐magnetic elements are very scarce. The present article illustrates Au ion implantation as an alternative tool to study the structural and magnetic properties in the Bi2Se3 nanocrystals grown by the chemical vapor deposition. The as‐grown pristine Bi2Se3 exhibits triangular and hexagonal plate‐like morphology, which undergoes structural distortion with increased Au ions. The room temperature Raman spectra show defect‐induced phonon softening with ion fluence. The non‐magnetic Bi2Se3 exhibit room temperature ferromagnetic hysteresis that originates from Bi vacancies which is verified from the density functional theory (DFT)calculations. The incorporation of Au ions initially decreases the magnetic moment up to the fluence 1 × 1014 ions cm−2 and enhances at higher fluences due to the formation of Au nanoclusters. The experimental and DFT results suggest a competition between the Se “4p” states and Au “5d” states for the non‐monotonic behavior of magnetic properties. The present work on Au intercalation in Bi2Se3 can pave the way to design artificial topological insulator devices for potential technological applications for future spintronics and quantum computations.