Nanocrystalline powders of Fe-doped SnO2 (Sn1-xFexO2) (x = 0.00, 0.01, 0.03, 0.05) were prepared by a hydrothermal method. The powders were calcined in argon atmosphere at 600 °C for 2 h, causing phase transition from diamagnetic and weak ferromagnetic behavior to a ferromagnetic state. No trace and other magnetic impurity phases was detected in the samples with Fe content up to 3%. The calcined samples of Fe-doped SnO2 revealed the room temperature ferromagnetism with highest magnetization values of 434.07 memu/g at 15 kOe for x = 0.05. The room temperature ferromagnetism of samples originated from oxygen vacancies that occurred in the argon calcination process. In particular, oxygen vacancy shows a significant role in ferromagnetic coupling corresponding to F-center interaction.

We report on the room-temperature ferromagnetism in carbon nanofibers. Carbon nanofibers were fabricated using sequential electrospinning of polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP). The morphologies, crystal structures, chemical bonding states and magnetic properties were characterized for three different polyacrylonitrile (PAN) to polyvinylpyrrolidone (PVP) weight ratios (10:0, 7:3 and 6:4) of PAN/PVP. The as-spun PAN/PVP were carbonized in three steps; stabilization, carbonization and activation at 800 ºC to obtain carbon nanofibers. The morphology and structure of the carbon nanofibers (CNFs) were completely characterized by field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) and Raman spectroscopy. The elemental composition and the chemical bonding of CNFs were analyzed by x-ray photoelectron spectroscopy (XPS), the magnetic properties of CNFs were measured by vibrating sample magnetometer (VSM) at room-temperature. XRD patterns showed the phase of amorphous carbon structure. The average diameter sizes of the carbon nanofibers ranged from 340 to 484 nm. Raman analysis was used to determine the carbon qualities in the samples by the numbers of sp3/sp2 hybridized atoms. Chemical analysis with XPS indicated that there were no magnetic contaminants in the samples. The PAN/PVP weight ratio of 6:4 showed ferromagnetic carbon nanofibers with the highest specific magnetization as ~144.2 memu/g at 300 K. These results inspire us to further research the potential of carbon materials, as a completely new class of magnetic devices. This will aid the development of new technologies in the near future.