Crystal field levels and fine structure of the ground orbital state for high spin Fe²⁺ and Fe⁴⁺ ions in YBa₂(Cu₁₋ₓFeₓ)3O₇₋δ

Czeslaw RUDOWICZ, Maolu DU, Yau Yuen YEUNG

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12 Citations (Scopus)

Abstract

Crystal field energy levels within the whole 3d⁶ and 3d⁴ configuration and the fine structure of the ground orbital for high spin Fe²⁺ and Fe⁴⁺ ions at several possible sites in YBa₂(Cu₁₋ₓFeₓ)3O₇₋δ [YBCO] have been investigated. The calculations for three cases,
namely ⁵D approximation, (⁵D and ³Γᵢ) approximation and full diagonalization, show that the contribution to the splitting of the ground state due to spin-singlets (¹Γᵢ) is negligible but that due to spin-triplets (³Γᵢ) is not negligible. Especially, in the case of Fe²⁺ in Cu(1) octahedral site, the spin-triplets contribution induces a change of the spin-ground state from Γ'₄ to Γ'₁. The dependence of the fine structure splittings on Fe concentration x in YBCO for Cu(1) octahedral and Cu(2) pyramidal sites is also investigated. The phase transition from orthorhombic to tetragonal structure at Fe concentration x ≊ 0.04 results in a degeneration of levels in the case of Fe²⁺ and Fe⁴⁺ in Cu(1) octahedral site at x > 0.04. In the case of Fe²⁺ and Fe⁴⁺ in Cu(2) pyramidal site a large variation of the ground state fine structure splittings is observed with increasing Fe concentration from low values to x = 0.04, but the splittings are almost constant at x greater than 0.04. The results corroborate our previous findings from the microscopic spin-Hamiltonian analysis within the ⁵D term on the large zero-field splitting for the Fe²⁺ and Fe⁴⁺ ions in YBCO. The present approach offers an improvement over the ⁵D approximation, which turns out to be inadequate for some ion/site cases because of strong contribution to the zero-field splitting due to the spin-triplet states. Copyright © 1993 Published by Elsevier Ltd.
Original languageEnglish
Pages (from-to)733-744
JournalJournal of Physics and Chemistry of Solids
Volume54
Issue number6
DOIs
Publication statusPublished - Jun 1993

Citation

Rudowicz, C., Du, M., & Yeung, Y. Y. (1993). Crystal field levels and fine structure of the ground orbital state for high spin Fe²⁺ and Fe⁴⁺ ions in YBa₂(Cu₁₋ₓFeₓ)3O₇₋δ. Journal of Physics and Chemistry of Solids, 54(6), 733-744. doi: 10.1016/0022-3697(93)90134-D

Keywords

  • Orthorhombic crystal field
  • Energy levels
  • 3d⁴ and 3d⁶ ions
  • Orbital singlet ground state
  • Fine structure
  • Spin-Hamiltonian
  • High Tc
  • Superconductors

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