Dopant site occupancies and iron valence states in SrZnxFe18−xO27 W-type hexaferrites using site-selective X-ray/electron spectroscopy.

Zn-doped W-type Sr hexaferrite (SrZn x Fe 18 − x O 27 ; SrZn x -WHF) is an anticipated rare-earth-free hard magnetic material with strong magnetocrystalline anisotropy and saturation magnetization. To examine the origin of its high magnetic performance, the site distribution of Zn over seven crystallographically inequivalent Fe sites and the site-dependent valence states of Fe were investigated using site-selective elemental/chemical analysis techniques. The dominant occupation of Zn2+ at the 4e tet(S) and 4f tet(S) tetrahedral sites was determined quantitatively using high-angular-resolution electron-channeling X-ray spectroscopy and statistical data analysis. The combined application of high-angular-resolution electron channeling electron spectroscopy and atomic-column resolution scanning transmission electron microscopy–electron energy-loss spectroscopy helped unambiguously clarify that most of the Fe2+ ions existed at the 6g oct(S-S) octahedral site. Density functional theory calculations have shown that Zn doping leads to a redistribution of the charges toward Fe ions at this site. This redistribution preserves the local charge balance and amplifies the total number of parallel spins. Hence, the enhanced magnetocrystalline anisotropy and saturation magnetization in SrZn x -WHF can be inferred to originate from the charge redistribution at the 6g oct(S-S) site, which is influenced by the presence of nonmagnetic Zn. [Display omitted] • Zn-doped W-type Sr hexaferrites were investigated by TEM and DFT calculations. • Site-dependent dopant occupancies and Fe valence states were examined. • Preferential occupation sites of doped Zn²⁺ and existing Fe²⁺ were different. • Charge redistribution among Fe sites compensates for local charge imbalance. • Zn site distribution and charge redistribution improved the magnetic performance. [ABSTRACT FROM AUTHOR]