Room temperature ferromagnetism in Sn_1-xV_xO ₂ films prepared by sol-gel method

The structure and magnetic properties of Sn_1-xV _xO₂ (x=0.02-0.22) thin films fabricated on Si (111) substrate using a sol-gel method and spin coating technique have been investigated. All the samples have pure rutile polycrystalline structure and exhibit room temperature ferromagnetism. The magnetic moment per V reaches 2.92 μ_B for the Sn_0.98V_0.02O₂ film and drops rapidly as V content is increased. X-ray photoelectron spectroscopy study reveals that vanadium is in V⁴⁺ chemical state. Various annealing treatments were performed to explore the origin of the ferromagnetism. It is found that the ferromagnetism of Sn_0.98V_0.02O₂ film disappears after annealing in a rich-oxygen atmosphere and occurs again after annealing in a low vacuum condition. Furthermore, an annealing in Sn vapor leads to the decrease in ferromagnetism. These results confirm that the oxygen vacancies play a critical role in introducing ferromagnetism of Sn _1-xV_xO₂ films; therefore, the origin of the ferromagnetism in our samples can be understood in the framework of the bound magnetic polaron model.