Atomic-Scale Imaging of Dopant Sites in a Ni-Doped Ideal Normal Spinel ZnFe₂O₄ Nanofiber and Its Correlated Magnetism Origin

Direct identification of the cationic occupation in Ni-doped normal spinel ZnFe 2 O 4 is a prerequisite for understanding the physical mechanism of its tunable magnetic properties and further oriented synthesizing the specific functional ferrite materials. However, the precise occupation of cations in Ni-doped ZnFe 2 O 4 is still in debate, and their atomic imaging in real space is lacking. Herein, we showcase an ordering distribution of cations in Ni-doped normal spinel ZnFe 2 O 4 by the direct observation. Our data evidently clarified that divalent Zn 2+ cations occupied all tetrahedral sites and trivalent Fe 3+ cations occupied all octahedral sites in the ZnFe 2 O 4 single-particle-chain nanofibers. When Ni was doped, Ni 2+ preferentially occupied the octahedral sites, and the excess Fe 3+ was squeezed to the tetrahedral sites. Electron holography and micromagnetic simulations further disclose that the shape anisotropy and dipolar anisotropy determined the magnetic moment distributions of the Ni-doped ZnFe 2 O 4 .