Structural Defects and Ferromagnetic Signature of V-Doped Sb 2 Te 3 Thin Films Grown on SrTiO 3 (001) Produced by RF-Magnetron Sputtering.

Thin films of V-doped Sb 2 Te 3 compounds were fabricated by co-deposition of Sb 2 Te 3 and V using rf-magnetron sputtering onto SrTiO 3 (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 (Sb 38 V 2 Te 60 ) is the Bi 2 Te 3 -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 Sb 2 Te 3 thin film and the SrTiO 3 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 Sb 2 Te 3 ). 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 Sb 2 Te 3 ). V 3+ ions substituting Sb sites should contribute to ferromagnetism at low temperatures.