Tuning the structural and magnetic properties of electrospun strontium-iron-oxide nanofibers with different stoichiometry

Nanostructured ferrites such as SrFeO3-x, SrFe2O4 and SrFe12O19 have great potential applications as permanent magnets due to their dynamic structures and excellent magnetic properties. However, the crystal structures of SrFeO3-x and SrFe2O4 nanomaterials remain controversial and their magnetic properties have large room for improvements. Attempting to tackle these problems, we fabricated strontium ferrite nanofibers with Sr:Fe ratios of 1:1, 1:2, and 1:12 using electrospinning followed by annealing at 850 degrees C in air. Scanning electron microscopy and transmission electron microscopy (TEM) examinations showed that the nanofibers with average diameters of 130-140 nm are made of nanograins. Through X-ray diffraction and TEM analysis, the crystal structures for nanofibers with Sr:Fe ratios of 1:1, 1:2, and 1:12 were identified as tetragonal SrFeO2.86, orthorhombic SrFe2O4 and hexagonal SrFe12O19, respectively. Extensive high-resolution TEM examinations showed the formation of stacking faults and edge dislocations in SrFeO2.86 nanofibers, and edge dislocations in SrFe12O19 nanofibers. Hysteresis loop measurements showed the three nanofibers had a similar coercive force (Hc), but different saturation magnetization (Ms) and residual magnetization (Mr). SrFe12O19 nanofibers possessed the largest Ms and Mr, while SrFeO2.86 nanofibers showed the lowest. The experimental Mr values agreed well with magnetic moments obtained from density functional theory calculations. This work clarifies the crystal structure of Sr-Fe-O nanofibers, and provides a good candidate for permanent magnet applications.

Automated summary

In this study, strontium ferrite nanofibers with different Sr:Fe ratios were fabricated using electrospinning and annealing. The crystal structures and magnetic properties of the nanofibers were analyzed through microscopy and X-ray diffraction. It was found that the nanofibers with Sr:Fe ratios of 1:1, 1:2, and 1:12 possessed tetragonal SrFeO2.86, orthorhombic SrFe2O4, and hexagonal SrFe12O19 structures, respectively. Hysteresis loop measurements showed slight variations in saturation magnetization (Ms) and residual magnetization (Mr) among the nanofibers. This study clarifies the crystal structure of strontium ferrite nanofibers and provides a potential candidate for permanent magnet applications.