Magnetic and Interfacial Characteristics of CMOS Compatible Sputtered Topological Insulator/Ferromagnet Heterostructures

The growth and magnetic properties of sputtered topological insulator (TI)/ferromagnet (FM) heterostructures are presented. Magnetron sputtering produced TI, Bi₂Te₃ (BT) with varying crystalline order: ranging from largely amorphous to highly c-axis-oriented. A giant enhancement in Gilbert damping in TI/FM heterostructures was observed for c-axis oriented BT. Heterostructures of BT/Ni₈₀Fe₂₀ (Py) produced interface phases of Ni-intercalated BT (Bi₂Te₃:Ni). The Bi₂Te₃:Ni interface layer was found to support a topologically nontrivial, novel AFM phase [1]. The AFM exchange interaction strength was found to decrease dramatically for the highly amorphous BT sample [2], as evidenced by the reduction in exchange bias in hysteresis loop measurements, from 8 mT to 1 mT at 6 K, and reduction in Neél temperature from 63 K to 20 K. Further, we performed spin-torque ferromagnetic resonance experiments in the BT/Py heterostructures taking into account the distinct interface layers, showing a larger spin-Hall angle in amorphous TIs compared with the c-axis oriented TIs by ~25%, which aligns with current understanding of sputtered TIs in literature. These results pave the way for the integration of sputtered TIs in industrial CMOS devices.