Structure and Magnetic Properties of Exchange-Coupled Pairs [Ni3+–$${\text{O}}_{\text{int}}^{ - }$$]6– in Monocrystalline BaF2: An EPR Study

In BaF2, a crystal of the fluorite structure group, in a helium atmosphere with small additions of fluorine and oxygen, paramagnetic complexes [NiF4F4Oint]6–(C4v) were synthesized by diffusion from the surface. These complexes are stable associates of a trivalent nickel ion with an interstitial oxygen ion $${\text{O}}_{{{\text{int}}}}^{ - }$$ . The molecular structure of the synthesized complexes was studied by the electron paramagnetic resonance method at frequencies of 9.65, 34.35, and 94–265 GHz in the temperature range from 4.2 to 120 K. It was shown that the studied complex is formed by Ni3+(3d7, 4F, S = 3/2) and O–(2p5, 2P, S = 1/2) ions. The Ni3+ ion replaces the Ba2+ lattice cation in the crystal, and the O– ion is located in the adjacent interstitial site in one of the crystallographic directions $$\left\langle {001} \right\rangle .$$ It was determined that, in the synthesized complexes, the ferromagnetic exchange interaction between the Ni3+ and O– ions occurs.