Narrow Results

In the past years, the typical high Tc superconductor YBa₂Cu₃O₆ has been extensively studied by many authors. And electron paramagnetic resonance (EPR) studies of rare-earth (Re³⁺) ions in high-Tc oxide superconductors have attracted much interest because they can provide valuable information on spin-lattice relaxation, exchange interactions and the ground state properties of Re³⁺ ions, which are further employed as sensitive probes of spin dynamics in high-Tc superconductor. The EPR anisotropic g factors of Dy³⁺ in YBa₂Cu₃O₆ crystal has been measured by M.R. Gafurov et al., and there is no theoretical explanations related to the crystal structural data. In this paper, parameters g factors for Dy³⁺ in YBa₂Cu₃O₆ are theoretically studied from the perturbation formulas of these parameters for a 4f⁹ ion in tetragonal symmetry. In these formulas, the contributions to the EPR parameters from the second-order perturbation terms and the admixtures of various excited states are taken into account. The related crystal-field parameters are determined from the superposition model and crystal structural data. The theoretical results show reasonable agreement with the experimental values.

It is of interest for layered oxides containing copper because they are related to high temperature superconductivity. Among them, LaSrAl_1-xCu_xO₄ solid solution has received much attention due to its elastic and elasto-optic properties and application as promising substrate for high-T_c superconducting thin films. So many theoretical and experimental works have been done to understand the several characteristics of the LaSrAl_1-xCu_xO₄ materials. In this paper, the electron paramagnetic resonance g factors g_//, g_⊥ and hyperfine structure constants A_//, A_⊥ for the tetragonal Cu²⁺ center in LaSrAl_1-xCu_xO₄ solid solution are theoretically explained by the method of diagonalizing the full Hamiltonian matrix. The related crystal field parameters are calculated from the superposition model and the local structural parameters of the impurity Cu²⁺ occupying the host Al³⁺ site. The superposition model parameters used in this work are comparable with those for similar tetragonal (CuO₆)^10- clusters in the previous works. The calculated results are in reasonable agreement with the observed values. The results are discussed.

The spin-Hamiltonian parameters (g factors g_i and hyperfine structure constants A_i, where i = x, y, z) and optical spectrum band positions of the Yb³⁺ ion in the rhombically-distorted Tm³⁺ site of Tm₃Al₅O₁₂ garnet crystal are calculated by a complete diagonalization (of the energy matrix) method, in which the Zeeman and hyperfine interaction terms are also included in the conventional Hamiltonian. From the calculations, the observed spin-Hamiltonian parameters of Tm₃Al₅O₁₂:Yb³⁺ are explained reasonably and the optical spectrum band positions are suggested. The rationality of these suggested optical spectrum band positions is discussed by comparing them with the observed values of Yb³⁺ ions in similar aluminum garnet (Yb₃Al₅O₁₂, Y₃Al₅O₁₂ and Lu₃Al₅O₁₂) crystals.

Six crystal field energy levels obtained from the photoluminescence spectra of Yb³⁺-doped CuInS₂ semiconductor crystal are calculated from the diagonalization (of energy matrix) method. The root-mean-square (r.m.s) deviation σ is 4.5 cm^-1 and so the calculated results are in good agreement with the experimental values. The local tetragonal distortion angle θ for the Yb³⁺ center in CuInS₂ (which is different from the corresponding angle θ_h in the host crystal) is obtained from the calculation.

The calculated EPR parameters are in reasonable agreement with the observed values. The important material Cs₂NaYCl₆ doped with rare earth ions have received much attention because of its excellent optical and magnetic properties. Based on the superposition model, in this paper the crystal field energy levels, the electron paramagnetic resonance parameters g factors of Dy³⁺ and hyperfine structure constants of ¹⁶¹Dy³⁺ and ¹⁶³Dy³⁺ isotopes in Cs₂NaYCl₆ crystal are studied by diagonalizing the 42 × 42 energy matrix. In the calculations, the contributions of various admixtures and interactions such as the J-mixing, the mixtures among the states with the same J-value, and the covalence are all considered. The calculated results are in reasonable agreement with the observed values. The results are discussed.

The six coordinated Co^IIIoxophlorin have been studied with imidazole, pyridine and t-butylcyanide as axial ligands using B3LYP, BV86P and MO6-2X methods. Conversion between two isomers [(L)₂Co^III(PO)]${}^{†}$ and [(L)₂Co^III(PO)]${}^{\left|\right|}$ can be occurred at various spin multiplicities, namely singlet, triplet and quintet states. L is employed to show axial ligand namely, imidazole or pyridine. London forces have a basic role in the stability of the mentioned complexes due to non-specific solvent effects. The latter fact has been obtained using the PCM model. Also, it is specified that minimum geometries have not been obtained for some parallel or perpendicular six-coordinated complexes with special axial ligands at a finite spin state. The B3LYP method indicates that one and three $\alpha$-electron can be found on the Co atom in every optimized complex at triplet and quintet spin states, respectively. Also, another $\alpha$-electron is placed on the ring of oxophlorin. This fact is obtained for different isomers of [(IM₂(Co^III(PO)] and [(Py)₂Co^III(PO)] at triplet and quintet spin states, while these complexes are optimized using B3LYP. Besides, results obtained from B3LYP show that the most stable state for six coordinated Co^IIIoxophlorin with any axial ligand is the singlet state. Based on crystal field theory and molecular orbital theory, electron configuration and hybridization of cobalt in [(IM)₂Co^III(PO)] at singlet state can be written as t₂g⁶ eg⁰ and sp³d², respectively. Former electronic configuration indicates a strong field with low spin for d orbitals of cobalt, and latter hybridization is expected for a metal with a coordination number of 6 in a complex with O_h symmetry. The results obtained are completely satisfied by NBO analysis.