Empirical correlation of ferromagnetism and electronic structure in Fe and Ni co-doped SnO2 solid solutions: An X-ray analysis using maximum entropy method

The phase-pure magnetic semiconducting Fex/2Nix/2Sn1-xO2 solid solutions with x = 0.03, 0.06, 0.09, and 0.12, were prepared by a cost-effective room-temperature one-step co-precipitation method. XRD peak red-shift reveals lattice compression due to the doping of low/similar ionic radii of Fe3+, Ni3+, and Ni2+ in the Sn4+ lattice, which is also confirmed by the EPR results. Maximum entropy method (MEM)-based electronic structure confirmed interstitial charge accumulation of 6.79 % and 6.05%, forming non-nuclear maxima in 3% and 12% doping systems, respectively, which reduces considerably the ferromagnetism. In addition, pure polar covalent apical and equatorial (Fe/Ni/Sn) - O bonding without interstitial charge accumulation is a key factor for maximum ferromagnetism. A perfect-fitting of the pair distribution function (PDF) and its correlation to charge accumulation at interstitial and regular lattice points in comparison with MEM results provides hope in PDF using low-Q XRD data. The samples with 9% and 6% dopants showed soft ferromagnetism with magnetization (0.0416 and 0.0372) emu/g respectively, which are helpful for magnetic semiconducting applications. The ferromagnetic and antiferromagnetic coupling between interstitial charges' local magnetic domains causes positive exchange anisotropy (exchange bias) in 3% and 12% compositions. The novel and empirical correlation between magnetism and the MEM-based electronic structure is the highlight of this study.