Yuhua Xiao

Room temperature ferromagnetism in Sn1−xVxO2 films prepared by sol-gel method

The structure and magnetic properties of Sn1−xVxO2 (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 2.92μB for the Sn0.98V0.02O2 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 Sn0.98V0.02O2 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 Sn1−xVxO2 films; therefore, the origin of the ferromagnetism in our samples can be underst...

Room temperature ferromagnetism of Sn1−xCoxO2−δ films fabricated by sol-gel method

Co-doped SnO2 thin films were fabricated by sol-gel method. All the samples have pure rutile polycrystalline structure and exhibit room temperature ferromagnetism (RTFM). Sn1−xCoxO2−δ films spin coated on Si (111) substrate have larger magnetic moment than those on Si (amorphous) substrate. X-ray photoelectron spectra reveal that cobalt exists as Co2+ in samples and Co57 spin-echo nuclear magnetic resonance experiment did not find Co clusters. Interestingly, the magnetic moment per Co atom decreases with the increase in Co content. The results of the annealing at oxidizing and vacuum atmospheres show that oxygen vacancies play a crucial role in producing ferromagnetism, implying that the origin of RTFM can be understood by a bound magnetic polaron model.

Structure and Magnetic Properties of Sn

We have studied room-temperature ferromagnetism (RTFM) in Sn1 - xCoxO2 powders and films fabricated by the sol-gel method. Our X-ray diffraction, high-resolution transmission microscopy, and X-ray photoelectron spectroscopy results show that all the samples have a pure rutile structure, and Co ions have a chemical valence of 2+. In addition, the magnetic moment per Co ion drops rapidly with the increase of Co content. Interestingly, Sn 1 - xCo xO 2 films spin-coated on a Si (111) substrate have much larger magnetic moment than powder samples, because film samples have larger domain volumes, which may induce stronger long-range magnetic exchange coupling.