Realizing ferromagnetic ordering in SnO2 and ZnO nanostructures with Fe, Co, Ce ions

Abstract

We report the defects/vacancies that attribute to room temperature ferromagnetism in SnO₂ in contrast to ZnO [Phys. Chem. Chem. Phys., 2016, 18, 5647], which has observed ferromagnetic ordering below room temperature, since both the systems involve similar dopant Fe, Co, and Ce ions. The Fe, Co, Ce doped SnO₂ nanostructures were synthesized by a sol–gel process. The Rietveld refinement of the X-ray diffraction data detects a rutile SnO₂ structure, with structural defects due to the deformation of the unit cell with doping. The pure, Fe and Co doped SnO₂ have nanoparticle formation that is induced to nanorods with Ce co-doping. However, ZnO retained a nanorod-type shape with Fe and Co ions and changed to nanoparticles with Ce co-doping. The rutile SnO₂ structure and defect formation with Fe, Co, and Ce ions is also confirmed with Raman vibrational modes. The observed lattice defects due to oxygen vacancies are shown by the photoluminescence study. The weak room temperature ferromagnetism is observed with Fe and Co ions in SnO₂, which is enhanced with Ce ions. The zero field (ZFC) and field cooling magnetic measurements indicate an improvement in magnetization with a cusp in the ZFC curve at low temperature, observed due to an antiferromagnetic transition. It also induced variations in the magnetic coercive field due to the phenomenon of superparamagnetism, spin glasses, and magnetic clustered growth. This can be further confirmed with ac magnetic susceptibility measurements that show magnetic transitions as well as frequency dispersive and dependent behaviors of χ′(T)/χ′′(T). However, the Fe, Co, Ce doped ZnO exhibit paramagnetic behavior at room temperature due to favorable antiferromagnetic interactions and have a ferromagnetic transition at low temperature with little ferromagnetic cluster growth.