The EPR g factors g i (i = x, y, z) for the interstitial Ti 3+ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d 1 ion in rhombically compressed octahedra. The ligand octahedron in the impurity center is found to be less compressed than that on the host interstitial site due to the Jahn-Teller effect. The local compression parameter (≈0.026) and the rhombic distortion angle δφ (≈0.7 • ) around the impurity Ti 3+ are smaller than the host values (≈0.091 and 3.5 • ). The theoretical g factors based on the above local structural parameters are in good agreement with the experimental data. In addition, the g factors for a tetragonal interstitial Ti 3+ center are also reasonably interpreted.

The superhyperfine parameters T j ( j = x, y, z) for Cu 2+ in the squareplanar K 2 PdX 4 (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for an octahedral 3d 9 cluster, by considering both the contributions from the crystal-field and charge-transfer mechanisms. The related molecular orbital coefficients are determined from the cluster approach in a uniform way. Based on one adjustable proportional factor ρ for the orbital admixture coefficients, the calculated results of present work show reasonable agreement with the observed values.Keywords Electron paramagnetic resonance (EPR) · Superhyperfine interactions · Cu 2+ · K 2 PdX 4 (X = Cl, Br)

The anisotropic g factors g and g ⊥ of La2Ni0.5Li0.5O4 are theoretically investigated using the perturbation formulae of the g factors for a low spin (S = 1/2) 3d 7 ion in tetragonally elongated octahedra. The studied Ni 3+ (3d 7 ) center arises from the original Ni 2+ capturing one hole by Li + doping. The positive anisotropy ∆g (= g ⊥ − g ) can be ascribed to the lowest 2 A1g state due to the obvious (about 0.14 Å) tetragonal elongation of the oxygen octahedron around the Ni 3+ site via the JahnTeller eect, and the eective magnetic moment is also interpreted in a uniform way. The calculated results show good agreement with the experimental data, and the imperfection of the previous studies based on various adjusted tetragonal energy splittings without correlating to the local structure of the magnetic center is thus overcome in this work.

The local structure and the spin Hamiltonian parameters (the g factors g i (i = x, y, z) and the hyperfine structure constants A i ) for Cu 2+ -doped Ca(OD) 2 are theoretically investigated from the perturbation formulas of these parameters for a 3d 9 ion in an orthorhombically elongated octahedron. From the studies, the planar Cu 2+ -OD -bonds are found to experience the relative variation 'R (|0.014 Å) along the X and Y axes, while those parallel to the Z axis may undergo the relative elongation 'Z (|0.25 Å) due to the JahnTeller effect. The theoretical spin Hamiltonian parameters based on the above local lattice distortions agree well with the experimental data. As compared with the previous treatments, the improvements of the theoretical spin Hamiltonian parameters are achieved in this work by adopting the uniform calculation formulas and the tetragonal field parameters based on the superposition model.

The electron paramagnetic resonance (EPR) g factors g and g ⊥ of the tetragonal NdBa 2 Cu 3 O 6.1 are theoretically studied using the perturbation formulas of the g factors for a 4f 3 ion in tetragonal symmetry. In the calculations, the influences of the admixtures of various energy levels are considered, while the tetragonal field parameters are determined from the local structural data of Nd 3+ site using the superposition model. The theoretical g factors are in reasonable agreement with the observed values. The positive anisotropy g ⊥ − g is attributable to the elongation of the oxygen cube around Nd 3+ along the C 4 axis in NdBa 2 Cu 3 O 6.1 . The magnitude (average) of the g factors for NdBa 2 Cu 3 O 6.1 is lower than that for the previously observed NdBa 2 Cu 3 O 7−δ (0 < δ < 1). This can be ascribed to the different oxygen amount and the dissimilar local environments around Nd 3+ under different preparation conditions and parameters. Further, the lowest Kramers doublet of the present NdBa 2 Cu 3 O 6.1 is the unresolved Γ 7,8 , while that of NdBa 2 Cu 3 O 7 is Γ 6 .