The magnetization measurements at magnetic field up to 6 T obtained from newly grown hexagonal Cd_{1-x}V_{x}S (x ≈ 0.0004) are presented. The strong anisotropy of magnetization is observed at low temperatures (1.6 < T < 20 K). The data are well described by the crystal field model calculations taking into account static trigonal Jahn-Teller distortion and spin-orbit coupling.
We present a simple magnetic model for PrAl_{3}. The effects of crystal field are treated using a reduced set of levels and the corresponding wave functions are extracted from the actual crystal field levels of Pr^{+3} in a hexagonal symmetry. The exchange between 4f- and conduction-electrons are dealt within a molecular field approximation. An analytical magnetic state equation is derived and the magnetic behaviour discussed. The parameters of the model are estimated from a fitting of the inverse susceptibility of PrAl_{3} given in the literature.
We have derived the low-energy electronic structure of CoF₃, originating from the strongly-correlated 3d⁶ system of the Co³⁺ ion, taking into account the crystal-field interactions, with a relatively weak trigonal distortion, and the relativistic spin-orbit interaction. We have calculated from really first-principles the relevant crystal-field interactions. With the discrete electronic structure for 3d electrons we have described the magnetic properties (the value of the magnetic moment and its direction). The moment direction is determined by the local off-octahedral trigonal distortion proving the single-ion origin of the magnetocrystalline anisotropy. We evaluated the orbital moment and the strength of spin interactions responsible for the formation of the magnetic state. Our studies indicate that calculations of the electronic structure of a 3d compound for the physically-adequate description of the magnetic properties has to be performed at the meV scale.
Using the most rigorous approach of direct diagonalization of the Hamiltonian matrix constructed in the complete basis states (364 in number) of the Er^{3+} ion the observed magnetic susceptibility and anisotropy data of erbium sulphate octahydrate were simulated and the set of crystal field parameters was evaluated. This procedure automatically includes the effect of intermediate coupling and the J-mixing under the crystal field. It was also demonstrated that such rigorous calculation using complete basis states is necessary in order to evaluate the correct set of parameters which may widely differ from the values obtained from approximate calculations previously performed using partial number of basis states of the ion concerned.
Magnetic and electronic properties of NdPd_2Al_3 have been nicely described with the Nd^{3+} ions within the crystal-field theory revealing that all Nd atoms equally contribute to the temperature dependence of the paramagnetic susceptibility and of the heat capacity with the λ-peak. We consistently described paramagnetic and magnetically-ordered state. The fine electronic structure of the Nd^{3+} ion nicely correlates with the electronic structure of the U^{3+} ion in UPd_2Al_3 giving strong evidence for the trivalent uranium state in the isostructural heavy-fermion superconductor UPd_2Al_3.
The energy level scheme of the Nd^{3+} and Pr^{3+} ions in ferromagnetic Nd_{2}Fe_{14}B and Pr_{2}Fe_{14}B intermetallic compounds was evaluated on the basis of all known experiments. In calculations the effect of charge (Stark effect) and spin-dependent (Zeeman effect) interactions were taken into account by means of the crystal-field and molecular-field approximation, respectively. The derived energy level scheme is associated with the removal of the degeneracy of the lowest multiplet given by Hund's rules, i.e. ^{4}I_{9/2} (Nd^{3+}) and ^{3}H_{4} (Pr^{3+}). The revealed low-energy electronic structure (<25 meV = 200 cm^{-1}) is associated with many-electron states of the RE^{3+} ions. Magnetic and electronic properties resulting from this fine structure are compared with all known experimental results. The localized crystal electric field levels exist also in Nd_{2}CuO_{4}, an ionic compound which by doping with Ce becomes high-T_{c} superconductor, indicating the formation of crystal electric field states independently on the metallic or ionic state.
The spin Hamiltonian parameters (g-factors and the hyperfine structure constants) and local structure are theoretically studied for single Cu²⁺ ion in BaF₂ from the high-order perturbation formulae of these parameters for 3d⁹ ions in tetragonally elongated octahedra. In the calculations, the ligand orbital and spin-orbit coupling of the impurity Cu²⁺ are taken into account, based on the cluster approach. Due to the Jahn-Teller effect and size mismatching substitution, the impurity Cu²⁺ is found to be located at a distance of about 0.2 Å from the nearest fluorine plane. The signs of the hyperfine structure constants A_∥ and A_⊥ are suggested. The theoretical spin Hamiltonian parameters based on the above local structure are in good agreement with the observed values.
The electron paramagnetic resonance parameters (i.e., g factor, hyperfine structure constant and superhyperfine parameters) of KMgF_3:Cr^{+} are theoretically investigated from the perturbation formulae of these parameters for an octahedral 3 d^5 cluster. As for the calculations of g factor and hyperfine structure constant, both the contributions from the crystal-field and charge transfer mechanisms are included based on the cluster approach. The metal to ligand charge transfer contribution to the g-shift Δg ( ≈ g-2.0023) is the same (negative) in sign and much larger in magnitude as compared to the crystal-field one. The conventional argument that the charge transfer contributions to zero-field splittings are negligible for 3 d^5 ions in fluorides is no longer suitable for Δg analysis of KMgF_3:Cr^{+} due to the dominant second-order charge transfer perturbation term. The charge transfer contribution to hyperfine structure constant exhibits the same sign and about 4% of the crystal-field one. The unpaired spin densities of the fluorine 2s, 2pσ and 2pπ orbitals are quantitatively acquired from the relationships with the relevant molecular orbital coefficients using the uniform model. The present treatments are superior to the previous calculations of directly fitting the experimental superhyperfine parameters.
Working in the strongly-correlated crystal-field approach and in the strong hybridization limit we calculated the temperature dependence of the heat capacity of NiO in a wide temperature range, from zero temperature to 1200 K. Our calculations reproduce reasonably well experimental dependence including the λ-type peak at T_N of 525 K.
Magnetic properties of bulk wurtzite GaN:Cr single crystals were studied with the magnetic field applied parallel and perpendicular to the crystal wurtzite c-axis. Structure of the crystal was examined by the X-ray diffraction method. Strong anisotropy of magnetization at low temperatures (2-10 K) was observed. The experimental data suggest Cr to be in nonspherical d^4 configuration.
The uniaxial anisotropy of magnetic properties of SrLa_{1-x}Nd_{x}AlO_{4} single crystals (x = 0.01 and 0.05) was found from the measurements of temperature dependencies of magnetic susceptibility. Results of measurements, with magnetic field along a- and c-axis, are compared with the similar data obtained for CaNdAlO_{4} crystal. The successful description of experimental data was done in frames of the crystal field approximation. The anisotropy of magnetic susceptibility appears due to crystal field acting on magnetic neodymium ions in a system without exchange interactions.
The radioactive decay of ^{172}Lu → ^{172}Yb appears to be suitable for time-differential perturbed angular correlation measurements of quadrupole interaction. The technique was applied to study various phenomena in three compounds: Yb_3S_4, YbPO_4, Yb_2Co_3Ga_9. We were able to distinguish between Yb^{2+} and Yb^{3+} ions occupying different positions in the crystal lattice of Yb_3S_4. Crystal electric field parameters reproduced the temperature dependence of the quadrupole interaction of Yb in YbPO_4. Finally, the influence of hybridization on the 4f quadrupole moment in Yb_2Co_3Ga_9 is evidenced.
By considering weaker magnetic interactions (including spin-spin and spin-other-orbit interactions) in Hamiltonian, the spin-Hamiltonian parameters, including the zero-field splitting parameter D and g factors (g_∥, g_⊥) for 3d^{2(8)} ions in Al_2O_3 crystals have been investigated. The results show that the contributions to D, g_∥ and g_⊥ from the spin-orbit interaction are dominant. The contributions from weaker magnetic interactions to D decrease (increase) with increasing charge of impurity ions for 3d^2 (3d^8) ions.
The spin-Hamiltonian parameters (the g factors g_{i} and the hyperfine structure constants A_{i}, i = x, y, z) and local structure of the Cu^{2+} center in PbTiO_{3} are theoretically studied by using the perturbation formulae of these parameters for a 3d^{9} ion in an orthorhombically elongated octahedra. The orthorhombic center is attributed to Cu^{2+} occupying the host Ti^{4+} site associated with a nearest-neighbouring oxygen vacancy V_{O} along the c-axis, and the impurity Cu^{2+} off-center displacement ΔZ_{L} ( ≈0.18 Å) is smaller than that of the host Ti^{4+} site (ΔZ_{H} ≈ 0.3 Å). Meanwhile, the planar Cu^{2+}-O^{2-} bonds are found to experience the relative variation ΔR ( ≈ 0.098 Å) along the a- and b-axes, respectively, due to the Jahn-Teller effect and the size mismatching substitution of Ti^{4+} by Cu^{2+}. The theoretical spin-Hamiltonian parameters based on the above defect structure agree well with the observed values.
The Blume-Emery-Griffiths model for spins S=1 in a bilayer with z=5 nearest neighbours is studied with the use of Gaussian fluctuations approximation. The fluctuations of two molecular fields, connected with two order parameters, are introduced. Their influence on phase diagrams for non-negative values of the biquadratic coupling constant is taken under consideration. The results are compared with those obtained by the mean-field approximation and discussed.
A general discussion of the simulation procedure of the full susceptibility tensor and isothermal magnetization pseudovector for compounds comprising weakly-interacting magnetic centers is presented. A single-crystal-sample as well as a powder-sample case are considered. The procedure is used to obtain explicit expressions for the full susceptibility tensor for spins S = 1, 3/2, 2, and 5/2 for non-vanishing rhombic local anisotropy and any form of spectroscopic tensor.
Zero-field splitting parameters obtained from EPR X-band experiments of Baran et al. (1985) and Yeom et al. (1992) are reanalyzed. Transformation relations are derived to express the two sets of data in the same axis system. Problems arising from using a truncated zero-field splitting Hamiltonian in fitting the experimental data are elucidated. Low-symmetry aspects in EPR spectra of Mn^{2+} at Bi^{3+} sites in BiVO_{4} single crystal are considered. Good agreement for orthorhombic parameters b^{0}_{2} and b^{2}_{2} is obtained indicating that the centres observed in the two cases are the same Mn centres. The remaining b^{q}_{k} parameters accounting for the actual site symmetry around Mn^{2+} impurity which seems to be lower than orthorhombic in the ferroelastic phase cannot be unambiguously determined from the existing EPR data.
We investigated magnetoreflectance and magnetization of highly diluted bulk Cd_{1-x}Mn_{x}Te crystals 0.2% ≤ x ≤ 10%. The exchange constant in terms of mean field approximation and virtual crystal approximation (the ratio of the heavy hole exciton splitting to mean spin per unit cell) was evaluated and found x-dependent. This deviation from the mean field approximation and virtual crystal approximation prediction is caused by the local potential introduced by Mn ions. We discuss the problem within a Wigner-Seitz approach and within a model of magnetic and chemical disorder based on the alloy theory.
Electron spin resonance (ESR) studies of two antibiotics, Cefaclor and Clarithromycin, have been performed in order to investigate concentration and dynamics of free radicals generated in these compounds due to thermal sterilization. For Cefaclor three combinations of temperature and heating time have been applied: 160°C, 170°C, 180°C for 120 min, 60 min, and 30 min, respectively, according to the pharmaceutical sterilization norm. Clarithromycin has been heated at 160°C for 120 min. The ESR lineshape has been investigated versus microwave power ranging from 2.2 mW to 70 mW. Electron spin-spin relaxation time has been estimated from the ESR lineshape analysis. Concentrations of radicals generated due to different sterilization procedures have been compared with the purpose to select the best sterilization scheme.
By using the complete diagonalization (of energy matrix) method based on the cluster approach (where the admixture between the d orbitals of d^{n} ion and p orbitals of ligands due to covalence effect is considered), the optical and electron paramagnetic resonance data (three optical band positions and four EPR parameters g_{∥}, g_{⊥}, A_{∥}, A_{⊥}) are calculated for the tetragonal Cu^{2+} center in Cu^{2+}-doped poly vinyl alcohol (PVA) passivated ZnSe nanocrystals with the defect model of Cu^{2+} in the interstitial octahedral site in ZnSe. The calculated results are near the experimental values. The tetragonal elongation of the Cu^{2+} octahedral cluster in ZnSe nanocrystals is obtained. The results are discussed.
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