Zhou Kang-Wei

Study of antiferromagnetic interaction of Mn–F–Mn cluster in KMgF3:Mn2+ and KZnF3:Mn2+ systems

The antiferromagnetic phenomena of the Mn-F-Mn spin cluster in KZnF3:Mn2+ and KMgF3:Mn2+ systems have been studied based on the Girerd-Journaux-Kahn (GJK) model and the Heitler-London (HL) model respectively. For the Mn ... Mn distance R in the range 3.4 < R < 4.6 Angstrom, the values of the exchange interaction parameter J calculated with the GJK model are greater by a factor 2 similar to 3 than those with the HL model and the results of J(GJK) are in good agreement with the experimental findings. This means that the contribution of the excited charge-transfer configuration (CTC) is considerably important and the main physical mechanism of the antiferromagnetic characteristics in KZnF3:Mn2+ and KMgF3:Mn2+ can be attributed to the combined effect of the direct exchange and the superexchange interactions

The spin-forbidden absorption spectrum of Fe2+ in orthopyroxene

In this article, we have established the energy matrices of the strong-field terms SΓ of the d4 (d6) electron configuration in a crystal-field with C2v symmetry. When we used this procedure to calculate the spin-forbidden absorption bands of Fe2+ in the M(2) site in orthopyroxene, we substituted the single-electron crystal-field energy levels (determined by the experimental results of the spinallowed spectrum) into the energy matrices instead of the single-electron crystal-field matrix elements. Thus, by means of only one parameter B (C=4B), most of the spin-forbidden bands of Fe2+ have been determined. Furthermore, when a similar treatment was made of the M(1) site of Ohsymmetry, the entire spin-forbidden spectrum of Fe2+ in orthopyroxenes could be semiquantitatively explained. This shows that the method is particularly useful for the calculation of spin-forbidden spectra of complexes with the d4 (d6) configuration in a low-symmetry site.

Antiferromagnetic exchange interaction of Cr3+ dimer in acid erothro chloride (NH3)(5)CrOHCr(NH3)(4)(H2O) Cl-5 center dot H2O and LaAlO3 : Cr3+ molecules

The antiferromagnetic phenomena of the chromium(III) dimer in acid erothro chloride [(NH3)(5)CrOHCr(NH3)(4)(H2O)]Cl-5. H2O and LaAlO3:Cr3+ have been explained in terms of the Girerd-Journaux-Kahn (GJK) model and the Heitler-London (HL) model, respectively. For the Cr ... Cr distance R in the range 3.2 < R < 4.4 Angstrom, the values of the exchange interaction parameter J calculated with the GJK model are higher by a factor 2-3 than those with the HL model. This means that the contribution of the excited charge-transfer configuration (CTC) is considerably important and the main physical mechanism of the antiferromagnetic characteristics in acid erothro chloride and in LaAlO3:Cr3+ can be attributed to the combined effect of the direct exchange and the superexchange interactions

A simplified strong-field scheme and the absorption spectrum of Mn2+ in rhodonite

From the analysis of the observed absorption spectrum data it is supposed that the Mn2 ions in rhodonite, (Mn, Ca, Fe)SiO3, mainly occupy the two sites Oh and C4v. After considering the spin-orbit coupling and the vibronic coupling, the complete absorption spectrum of the Mn2+ in rhodonite has been calculated for the first time, by means of a simplified strong-field scheme advanced in this paper. It is shown from the good agreement between the theoretical and experimental values that this viewpoint is reasonable and the method is correct. However, the theory does not eliminate the possibility of alternative explanations such as Mn2+ ions at sites of O or D4, D4h and D2d symmetry.

The fine structure levels and spin-singlet contributions to zero-field-splitting parameters of Cr2+ ion in CdGa2S4

A theoretical investigation is reported of the fine structure levels and the spin-singlet contributions to zero-field-splitting (ZFS) parameters for Cr2+ ion in CdGa2S4 crystals. Firstly, the complete energy matrix including all spin states for a 3d 4 ion in tetrahedral D 2d symmetry is constructed according the double-group chain in the strong-field scheme. Then, by diagonalizing the complete energy of electron–electron interactions, the crystal field and the spin–orbit coupling for the Cr2+ (3d 4) ion in CdGa2S4 crystal, the fine structure levels and the spin-singlet contributions to ZFS parameters a, D and F are calculated. The results show that the spin-singlet contribution to D is negligible, but the contributions to a and F are very important. So, to obtain more accurate ZFS parameters for 3d 4 ions in the tetrahedral crystals, all spin states should be considered.

Study of EPR zero-field splitting of iron–sulfur clusters in tetrahedral ZnS:FeIII system ☆

The EPR zero-field splitting of the iron-sulfur cluster in the ZnS:Fe-III system has been studied on the basis of the energy matrix for the electron-electron repulsion, the ligand-field and the spin-orbit coupling of a d(5) configuration ion with a trigonal symmetry. It is demonstrated that in order to reasonably explain the EPR zero-field splitting parameters a, D and (a - F), a positive ligand-field strength Dq for a d(5) electron configuration ion in a tetrahedron has to be employed. This means that the effective charge of each sulfur ion in ZnS is positive. This unusual result leads to the conclusion that in ZnS each sulfur ion may occur a quadricovalent argon state S2+ with sp(3) hybrid configuration and this conclusion is in accord with Paulings speculation

Magnetic theory for MnIII–O–MnIII spin-cluster in oxo-bridged covalent complex Mn2O(5-NO2saldien)2 ☆

Abstract A theoretical method for describing magnetic-exchange-interactions in covalent molecular systems is established by introducing covalent effect into Girerd–Journaux–Kahns (GJK) magnetic formula and adopting our Double-Slater-Function (DSF) calculation method. The calculations show that the exchange coupling parameter J depends sensitively on the covalent factor N; the stronger the covalent effect the stronger the antiferromagnetic exchange interaction; the direct- and kinetic- exchange interactions are both important. The calculation for MnIII–O–MnIII spin-clusters in Mn2O(5-NO2saldien)2 reveals that about 30% of the antiferromagnetic contribution comes from covalent effect, and that the theoretical values J=−111.02 to −138.85 cm −1 agree well with the experimental findings (J ( expt .) =−120 cm −1 ) .

The crystal field theory for D2d symmetric complexes and the splitting of d-orbitals of Mo5+ in Mo[S2CN(C2H5)2]4I3

The energy order assignment of the d-orbitals of Mo5+ in Mo[S2CN(C2H5)2]4I3 given by Jasimet al. (1985) is restudied and corrected. It is indicated that, in general, the energy order of the d-orbitals of D2d symmetric complexes is depending on the bond angles and bond lengths of the ligands, thus there cannot be any universal energy order.