Comparative Analysis of Experimental and Theoretical Zero-Field Splitting and Zeeman Electronic Parameters for Fe2+ Ions in FeX2·4H2O (X = F, Cl, Br, I) and [Fe(H2O)6](NH4)2(SO4)2

M. Zająca and C. Rudowicza,b aInstitute of Physics (IP), West Pomeranian University of Technology, al. Piastów 17, 70-310 Szczecin, Poland bVisiting Professor: Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań, Poland

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Spectroscopic and magnetic properties of Fe2+ (3d6; S=2) ions at orthorhombic sites in FeX2· 4H2O (X = F, Cl, Br, I) crystals are compared with those in [Fe(H2O)6](NH4)2(SO4)2 (FASH). The microscopic spin Hamiltonian modeling utilizing the package MSH/VBA enables prediction of the zero-field splitting parameters and the Zeeman electronic ones. Wide ranges of values of the microscopic parameters, i.e. the spin-orbit (λ), spin-spin (ρ) coupling constants, and the crystal-field (ligand-field) energy levels (Δi) within the 5D multiplet are considered to establish the dependence of the zero-field splitting parameters bkq (in the Stevens notation) and the Zeeman factors gi on λ, ρ, and Δi. By matching the theoretical spin Hamiltonian parameters and the experimental ones measured by EMR, the suitable values of λ, ρ, and Δi are determined. The novel aspect is prediction of the fourth-rank zero-field splitting parameters and the ρ (spin-spin)-related contributions, not considered in previous studies. The MSH predictions provide guidance for high-magnetic field and high-frequency EMR measurements.

DOI: 10.12693/APhysPolA.132.19 PACS numbers: 33.35.+r, 71.70.Ch, 71.70.Ej, 76.20.+q, 76.30.-v, 76.30.Fc, 87.80.Lg