Zero-field splitting of the ground state and local lattice distortions for Fe3+ ions at the tetragonal FeF5O cluster center in Fe3+:KMgF3 crystals

The relations between the zero-field splitting (ZFS) parameters and the structural parameters of the tetragonal FeF5O cluster center in Fe3+:KMgF3 crystals have been established by means of the microscopic spin Hamiltonian theory and the superposition model (SPM). On the basis of this, the local structure distortions, the second-order ZFS parameter D, the fourth-order one (a + 2F/3), and the energy level separations Delta(1) and Delta(2) of the ground spin state for Fe3+ ion doped in Fe3+:KMgF3 crystals are theoretically investigated. We use complete diagonalization method (CDM) and take into account the electronic magnetic interactions, i.e. the spin-spin (SS), the spin-other-orbit (SOO), and the orbit-orbit (OO) interactions, besides the well-known spin-orbit (SO) interaction. This investigation reveals that the replacement of O2- for F- and the induced lattice relaxation Delta R-2(O), combined with an inward relaxation of the nearest five fluorine ions Delta R-1(F) give rise to a strong tetragonal crystal field, which yields the large ZFS of the ground state. The theoretically calculated parameters D, (a + 2F/3), Delta(1), and Delta(2) for Fe3+:KMgF3 crystals are in good agreement with experimental ones when the five F- ions move toward Fe3+ by vertical bar Delta R-1(F)vertical bar = 6.40 x 10(-4) nm and the O2- ion toward Fe3+ by vertical bar Delta R-2(O)vertical bar = 10.55 x 10(-3) nm. (C) 2011 Elsevier B.V. All rights reserved.