Spectroscopic properties of Fe ions at tetragonal sites—Crystal field effects and microscopic modeling of spin Hamiltonian parameters for Fe (S=2) ions in K2FeF4 and K2ZnF4 |
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Authors: | C. Rudowicz D. Piwowarska |
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Affiliation: | Modeling in Spectroscopy Group, Institute of Physics, West Pomeranian University of Technology, Al. Piastów 17, 70-310 Szczecin, Poland |
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Abstract: | Magnetic and spectroscopic properties of the planar antiferromagnet K2FeF4 are determined by the Fe2+ ions at tetragonal sites. The two-dimensional easy-plane anisotropy exhibited by K2FeF4 is due to the zero field splitting (ZFS) terms arising from the orbital singlet ground state of Fe2+ ions with the spin S=2. To provide insight into the single-ion magnetic anisotropy of K2FeF4, the crystal field theory and the microscopic spin Hamiltonian (MSH) approach based on the tensor method is adopted. Survey of available experimental data on the crystal field energy levels and free-ion parameters for Fe2+ ions in K2FeF4 and related compounds is carried out to provide input for microscopic modeling of the ZFS parameters and the Zeeman electronic ones. The ZFS parameters are expressed in the extended Stevens notation and include contributions up to the fourth-order using as perturbation the spin-orbit and electronic spin-spin couplings within the tetragonal crystal field states of the ground 5D multiplet. Modeling of the ZFS parameters and the Zeeman electronic ones is carried out. Variation of these parameters is studied taking into account reasonable ranges of the microscopic ones, i.e. the spin-orbit and spin-spin coupling constants, and the energy level splittings, suitable for Fe2+ ions in K2FeF4 and Fe2+:K2ZnF4. Conversions between the ZFS parameters in the extended Stevens notation and the conventional ones are considered to enable comparison with the data of others. Comparative analysis of the MSH formulas derived earlier and our more complete ones indicates the importance of terms omitted earlier as well as the fourth-order ZFS parameters and the spin-spin coupling related contributions. The results may be useful also for Fe2+ ions at axial symmetry sites in related systems, i.e. Fe:K2MnF4, Rb2Co1−xFexF4, Fe2+:Rb2CrCl4, and Fe2+:Rb2ZnCl4. |
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Keywords: | Electron magnetic resonance (EMR) Optical spectroscopy Magnetism Crystal (ligand) field Microscopic spin Hamiltonian (MSH) approach Zero-field splitting (ZFS) parameter Tetragonal site symmetry Orthorhombic ZFS term Fe2+ ion in K2FeF4 Fe2+:K2ZnF4 Computer modeling package Transition ions in crystal |
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