Significant enhancement of ferromagnetism above room temperature in epitaxial 2D van der Waals ferromagnet Fe 5- δ GeTe 2 /Bi 2 Te 3 heterostructures.

Two-dimensional (2D) van der Waals (vdW) ferromagnetic metals Fe x GeTe 2 with x = 3-5 have raised significant interest in the scientific community. Fe 5 GeTe 2 shows prospects for spintronic applications since the Curie temperature T c has been reported near or higher than 300 K. In the present work, epitaxial Fe 5- δ GeTe 2 (FGT) heterostructures were grown by Molecular Beam Epitaxy (MBE) on insulating crystalline substrates. The FGT films were combined with Bi 2 Te 3 topological insulator (TI) aiming to investigate the possible beneficial effect of the TI on the magnetic properties of FGT. FGT/Bi 2 Te 3 films were compared to FGT capped only with AlO x to prevent oxidation. SQUID and MOKE measurements revealed that the growth of Bi 2 Te 3 TI on FGT films significantly enhances the saturation magnetization of FGT as well as the T c well above room temperature (RT) reaching record values of 570 K. First-principles calculations predict a shift of the Fermi level and an associated enhancement of the majority spin (primarily) as well as the total density of states at the Fermi level suggesting that effective doping of FGT from Bi 2 Te 3 could explain the enhancement of ferromagnetism in FGT. It is also predicted that strain induced stabilization of a high magnetic moment phase in FGT/Bi 2 Te 3 could be an alternative explanation of magnetization and T c enhancement. Ferromagnetic resonance measurements evidence an enhanced broadening in the FGT/Bi 2 Te 3 heterostructure when compared to FGT. We obtain a large spin mixing conductance of g ↑↓eff = 4.4 × 10 20 m -2 , which demonstrates the great potential of FGT/Bi 2 Te 3 systems for spin-charge conversion applications at room temperature.