Structural Defects and Ferromagnetic Signature of V-Doped Sb2Te3 Thin Films Grown on SrTiO3(001) Produced by RF-Magnetron Sputtering.

Abstract

Thin films of V-doped Sb2Te3 compounds were fabricated by co-deposition of Sb2Te3 and V using rf-magnetron sputtering onto SrTiO3(001) substrates kept at 570 K. The microstructures of the films were characterized using transmission electron microscopy (TEM) and electron diffraction. The crystal structure of the sputtered film (Sb38V2Te60) is the Bi2Te3-type structure with lattice parameters of a = 0.44 ± 0.03 nm and c = 3.02 ± 0.02 nm. A combination of cross-sectional and plan-view TEM observations revealed the preferential orientation of the c axis in the film's normal direction. A thin amorphous layer exists between the Sb2Te3 thin film and the SrTiO3 substrate. The interfacial amorphous layer relaxes the strain between the thin film and the substrate, and hence, it should promote the growth of a low-index atomic plane with a low surface free energy (i.e., (0001) of the Sb2Te3). The onset of ferromagnetic order was detected at temperatures below 70 K. A remarkable increase in magnetization was detected in the film's normal direction, which corresponds to the magnetic easy axis (i.e., c axis of the Sb2Te3). V3+ ions substituting Sb sites should contribute to ferromagnetism at low temperatures.