Structure and magnetic properties of impurity complexes [NiF₄F₄Fint] ^6- (C_4v) in the BaF₂ crystal: EPR study data

Impurity paramagnetic complexes [NiF₄F₄F_int]^6-(C_4v), which are a stable associate of a trivalent nickel ion with an interstitial fluorine ion F^–int, have been synthesized in a fluorite structure BaF₂ ionic crystals. The molecular structure of the synthesized complexes was studied by the method of electron paramagnetic resonance at frequencies of 9.39 and 34.25 GHz in the temperature range from 5 to 250 K. It is shown that in the studied complex, the Ni³⁺ ion (3d⁷, ⁴F, S = 3/2) replaced the lattice cation Ba²⁺, but, under the influence of F^–int in the neighboring internode of the octahedral type, shifted towards it from the center of the coordination cube occupied by it. Under the influence of the tetragonal symmetry crystal field, the electron spin levels of the complex split into two Kramers doublets |±1/2⟩, of which the doublet turned out to be the main one. The energy interval between doublets is approximately 114 GHz. A super-superfine structure is observed in the EPR spectra due to the interactions of the electron spin moment of the nickel ion with the nuclei of nine ligand fluorine ions. The parameters of these interactions are defined.