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 inNi-doped normal spinel ZnFe2O4is a prerequisite for under-standing the physical mechanism of its tunable magnetic propertiesand further oriented synthesizing the specific functional ferritematerials. However, the precise occupation of cations in Ni-dopedZnFe2O4is still in debate, and their atomic imaging in real space islacking. Herein, we showcase an ordering distribution of cations inNi-doped normal spinel ZnFe2O4by the direct observation. Ourdata evidently clarified that divalent Zn2+cations occupied alltetrahedral sites and trivalent Fe3+cations occupied all octahedralsites in the ZnFe2O4single-particle-chain nanofibers. When Ni wasdoped, Ni2+preferentially occupied the octahedral sites, and theexcess Fe3+was squeezed to the tetrahedral sites. Electronholography and micromagnetic simulations further disclose that the shape anisotropy and dipolar anisotropy determined themagnetic moment distributions of the Ni-doped ZnFe2O4