Local and long-range atomic/magnetic structure of non-stoichiometric spinel iron oxide nanocrystallites

Spinel iron oxide nanoparticles of different mean sizes in the range 10–25 nm have been prepared by surfactant-free up-scalable near- and super-critical hydrothermal synthesis pathways characterized using a wide advanced structural characterization methods to provide highly detailed description. The atomic structure is examined combined Rietveld analysis synchrotron powder X-ray diffraction (PXRD) data time-of-flight neutron powder-diffraction (NPD) data. local ordering further analysed pair distribution function (PDF) both total-scattering It observed that non-stoichiometric model based on tetragonal γ-Fe 2 O 3 phase with vacancy (space group P 4 1 2) yields best fit PXRD Detailed peak-profile reveals shorter coherence length for superstructure, which may be attributed vacancy-ordered domains being smaller than size crystallites and/or presence anti-phase boundaries, faulting or other disorder effects. intermediate stoichiometry between Fe confirmed refinement Fe/O scattering quantitative Mössbauer spectra. complemented nano/micro-structural transmission electron microscopy (TEM), elemental mapping scanning TEM, energy-dispersive spectroscopy measurement macroscopic magnetic properties vibrating sample magnetometry. Notably, no evidence found /γ-Fe core-shell nanostructure present, had previously suggested spinel nanoparticles. Finally, study concluded PDF (mPDF) method determine domain mPDF ferrimagnetic collinear spins ∼60–70% total nanoparticle sizes. present first has applied nanoparticles, establishing successful precedent future studies this technique.