Spin Hamiltonian Constants Research Articles

Evaluation of Spin Hamiltonian Parameters and Local Structure of Cu2+-doped Ion in xK2SO4–(50 – x)Na2SO4–50ZnSO4 Glasses with Various K2SO4 Concentrations

The spin Hamiltonian parameters (SHPs), i.e., g factors and hyperfine structure constants, and local structures are theoretically studied by analyzing tetragonally elongated 3d9 clusters for Cu2+ in xK2SO4–(50 – x)Na2SO4–50ZnSO4 glasses with various K2SO4 concentrations x. The concentration dependences of the SHPs are attributed to the parabolic decreases of the cubic field parameter Dq, orbital reduction factor k, relative tetragonal elongation ratio τ, and core polarization constant κ with x. The [CuO6]10– clusters are found to undergo significant elongations of about 17% due to the Jahn–Teller effect. The calculated cubic field splittings and the SHPs at various concentrations agree well with the experimental data.

Specific features of the EPR spectra of KTaO3: Mn nanopowders

The electron paramagnetic resonance spectra of KTaO3: Mn nanocrystalline powders in the temperature range from 77 to 620 K have been measured and studied for the first time. The change observed in the spectra has been investigated as a function of the doping level. The doping regions in which Mn2+ ions are individual paramagnetic impurities have been established, as well as the regions where the dipole-dipole and exchange interactions of these ions begin to occur. The spin-Hamiltonian constants for the spectrum of non-interacting individual Mn2+ ions have been determined as follows: g = 2.0022, D = 0.0170 cm−1, and A = 85 × 10−4 cm−1. A significant decrease in the axial constant D in the KTaO3: Mn nanopowder, as compared to the single crystal, has been explained by the remoteness of the charge compensator from the paramagnetic ion and by the influence of the surface of the nanoparticle. It has been assumed that the Mn2+ ions are located near the surface and do not penetrate deep into the crystallites.

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu2+ lattice sites, Cu2+(I) and Cu2+(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: gx = 2.0201 ± 0.002, gy = 2.0900 ± 0.002, gz = 2.1634 ± 0.002, Ax = (30 ± 2) × 10−4 cm−1, Ay = (40 ± 2) × 10−4 cm−1 and Az = (154 ± 2) × 10−4 cm−1. It was found that Cu2+ enters the lattice substitutionally. The ground-state wavefunction of the Cu2+ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.

Exchange dependence of the spin-Hamiltonian constants for antiferromagnetically coupled S-ion pairs

Experimental data that indicate the existence of an exchange-dependent contribution to single-ion spin-Hamiltonian constants for antiferromagnetically coupled S-ion pairs in diamagnetic crystals are reported and generalized.

Theoretical calculations of the spin-Hamiltonian parameters for the tetragonal Dy3+ center in HfSiO4 crystal

The spin-Hamiltonian parameters (g factors g(parallel to), g(perpendicular to) and hyperfine structure constants (161)A(parallel to), (161)A(perpendicular to), (163)A(parallel to), (163)A(perpendicular to)) for Dy(3+) at the tetragonal H(f)(4+) site of H(f)SiO(4) crystal are calculated from the diagonalization (of energy matrix) method. In the method, we add the Zeeman (or magnetic) and hyperfine interaction terms to the conventional Hamiltonian used in the calculations of crystal-field energy levels. The 66 X 66 energy matrix concerning the new Hamiltonian is established by considering the ground multiplet (6)H(15/2) and the first to fifth excited multiplets (6)H(J) (where J=13/2, 11/2,9/2, 7/2 and 5/2), and the crystal-field parameters in the energy matrix are calculated from the superposition model. From the calculations, the spin-Hamiltonian parameters of H(f)SiO(4):Dy(3+) are explained reasonably and the signs of hyperfine structure constants for (161)Dy(3+) and (161)Dy(3+) isotopes in H(f)SiO(4) are suggested. The results are discussed. (C) 2010 Elsevier B.V. All rights reserved.

Spin-Hamiltonian parameters and angular distortion for the trigonal Nd3+ center in congruent LiNbO3

The 52x52 energy matrix related to the ground multiplet (4)I(9/2) and the first to third excited multiplets (4)I(11/2), (4)I(13/2) and (4)I(15/2) for 4f(3) ions in trigonal crystal field under an external magnetic field is established. By diagonalizing the energy matrix, the spin-Hamiltonian parameters (g factor g(parallel), g(perpendicular) and hyperfine structure constants (143)A(parallel), (143)A( perpendicular), (145)A(parallel), (145)A( perpendicular)) of the trigonal Nd(3+) center in congruent LiNbO(3) crystal are calculated. The calculated results are in reasonable agreement with the experimental values. From the calculations, the negative signs of hyperfine structure constants are suggested and the angular distortion of the trigonal Nd(3+) center in LiNbO(3), which is unable to be determined by EXAFS measurement, is obtained. The results are discussed.

Magnetic anisotropy of a manganese carbonate antiferromagnet

It is well known from the scientific literature that to estimate the effect of an electric crystalline field on magnetically concentrated crystal anisotropy, an isostructural diamagnetic analog with close lattice parameters is used. The impurity of a magnetic substance sufficient for observation of electron paramagnetic resonance (EPR) spectrum of single ions is introduced into this analog. The constants determined by the EPR methods are then used to describe the energy levels (and hence anisotropy) by solving the equation for a single-ion spin Hamiltonian written in the molecular field approximation for a magnetically concentrated crystal. However, as a rule, it is impossible to find a diamagnetic analog with close enough lattice parameters. In the present work, the data of EPR investigations of single Mn ions in diamagnetic analogs of isostructural MnCO3 [1–4] are generalized and presented in the form of dependences of axial spin Hamiltonian constants Dcf and (a – F)cf on the hexagonal lattice constant ratio cH/aH (Fig. 1). The constant (a – F)cf is described by linear plus quadratic dependences on cH/aH (signs of constants Dcf and (a – F)cf are unknown for MgCO3 + Mn and ZnCO3 + Mn crystals). From these dependences, constants of the spin Hamiltonian for the MnCO3 crystal are determined, and single-ion contribution to the uniaxial anisotropy field HAcf(0) = 4Dcf + (a – F)cf is estimated for T = 0 K. A new single-ion exchange mechanism investigated recently in [5–7] can also contribute significantly to the MnCO3 anisotropy. The adequacy of the method used to study this mechanism can be judged only with allowance for all contributions (and, in particular, the single-ion contribution) and subsequent comparison of their sum with an experiment. The method of estimating the single-ion exchange contribution is analogous to the above-described one; the only difference is that EPR is measured for ion pairs. The contribution of manganese carbonate to the uniaxial anisotropy field ex A H was estimated from the constructed dependences of the single-ion exchange parameters on the lattice constants of isostructural diamagnetic analogs [5]. Table 1 tabulates contributions of the main mechanisms to the uniaxial MnCO3 anisotropy field for T = 0 K. Here HAdip is the dipole field contribution, HAT = HAcf + ex A H + HAdip is the total field estimated theoretically, and HA is the experimental value of the anisotropy field. From a comparison of HAT with the experiment it can be seen that the data are in good agreement, which testifies to the adequacy of estimated contributions (see Table 1).

Spin-Hamiltonian parameters and defect structure for tetragonal Pr4+ centers in ZrSiO4 crystal

A complete diagonalization (of energy matrix) method (CDM) for 4f(1) ions in tetragonal symmetry under an external magnetic field is applied to calculate the spin-Hamiltonian parameters (g factors 911, g(parallel to),g(perpendicular to) and hyperfine structure constants A(parallel to), A(perpendicular to)) for Pr(4+) ion at the tetragonally distorted dodecahedral (D(2d)) Zr(4+) site in ZrSiO(4) crystal. In the calculations, the crystal-field parameters used are acquired from the superposition model which enables correlation of the crystal-field parameters and hence the spin-Hamiltonian parameters with the defect structural data. The calculated spin-Hamiltonian parameters are in keeping with the experimental values and the defect structural data of the tetragonal Pr(4+) center in ZrSiO(4) crystal are obtained. The results are discussed. (C) 2009 Elsevier B.V. All rights reserved.

ESR of copper-doped sodium citrate

Single crystal ESR spectra of Cu 2 + ion doped in sodium citrate are reported at room temperature. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with g x = 2.1076 ± 0.002 , g y = 2.1289 ± 0.002 , g z = 2.4454 ± 0.002 , A x = ( 40 ± 2 ) 10 - 4 cm - 1 , A y = ( 62 ± 2 ) 10 - 4 cm - 1 and A z = ( 78 ± 2 ) 10 - 4 cm - 1 . It is found that Cu 2 + enters the lattice as a substitutional impurity replacing an Na + ion. The ground state wave function of Cu 2 + ion in this lattice is also determined from the spin-Hamiltonian constants obtained from ESR results. It is found that the ground state is predominantly | x 2 - y 2 〉 . With the help of the optical absorption study, the nature of bonding in the complex has also been discussed.

Ligand hyperfine interaction in Gd3+ tetragonal centers in CaF2 and SrF2 and the structure of the impurity nearest surroundings

ENDOR experimental spectra of Gd3+ tetragonal impurity centers in CaF2 and SrF2 crystals were used to determine the superhyperfine interaction (SHFI) constants of the impurity with 19F nuclear spins of its first coordination sphere and the compensator ion. The distances in the Cd3+F9 complex were estimated within the model of isotropic SHFI constants suggested in [1]. An analysis of the data on the SHFI and spin-Hamiltonian constants [2] in terms of the superposition model indicates significant changes in the contributions (due to the Gd3+ mixed states) to these parameters for the tetragonal centers in comparison with the corresponding contributions for the cubic and trigonal centers in the same crystals.

ESR of Copper Doped Calcium Propionate

Electron spin resonance (ESR) of Cu 2+ doped calcium propionate has been studied at room temperature. Spin Hamiltonian parameters are calculated from the ESR absorption spectra which are g x =2.1285±0.002, g y =2.1868±0.002, g z =2.2205±0.002, A x =(121±2)×10 -4 cm -1 , A y =(140±2)×10 -4 cm -1 and A z =(142±2)×10 -4 cm -1 . It is found that Cu 2+ enters the lattice interstitially. The ESR results indicate that the copper complex possesses rhombic symmetry. The ground state wave function of Cu 2+ ion in this lattice is also determined from the spin-Hamiltonian constants obtained from ESR results. It is found that the ground state is predominantly | x 2 - y 2 >.

Determination of the environment of Fe3+using the fourth order Spin-Hamiltonian constants, its power and limits

Determination of the environment of Fe³⁺using the fourth order Spin-Hamiltonian constants, its power and limits

Magnetic anisotropy of antiferromagnet (CH3)4NMnCl3

The parameters of the electron paramagnetic resonance (EPR) spectra of S ion pairs in diamagnetic crystals are analyzed. A relation between the spin Hamiltonian constants is established for solitary ions and pairs for (CH3)4NCdCl3: Mn2+ crystals. In contrast to solitary ions, an additional contribution (which is a linear function of the exchange field) to the “single-ion” spin Hamiltonian constants appears in the case of pairs. It is shown that anisotropic exchange mechanisms do not play a significant part in the formation of the axial constant of the spin Hamiltonian for this crystal. Some aspects of the method of studying “single-ion” anisotropy predicted by the two-ion model are developed with the help of an isostructural diamagnetic analog with impurity concentration of the paramagnetic ions of a magnetically concentrated substance sufficiently high for observing the EPR spectrum of the pairs. It is found that the microscopic quantities determined partially from the EPR spectra for pairs and solitary Mn2+ ions in (CH3)4NCdCl3 are in accord with the experimental value of the effective field for the (CH3)4NMnCl3 crystal anisotropy which can be described primarily by the dipole and “single-ion” mechanisms of the exchange origin.

Electron paramagnetic resonance study of at position in forsterite

In an electron paramagnetic resonance study of a synthetic single crystal of forsterite, , one spectrum of with maximum local symmetry -1 was observed. This spectrum arises from substituted for at the position. The second-order constants of the spectrum are and . All the fourth-order spin-Hamiltonian constants are given: they are much larger than generally observed in silicates. The zero-field splitting of the EPR spectrum is larger than the energy of the hyperfrequency field in the Q band; this case is near the limit of possibility of calculating the fourth-order constants of the spin Hamiltonian. It is shown that the substitution of for does not strongly modify the local structure and that there is no local charge compensation.

Temperature dependence of Mn2+ EPR in Sn2P2S6 near the phase transition

The X-band EPR spectrum of Mn2+ in Sn2P2S6 was studied in the temperature rangeT=223–363 K. At room temperature the spin-Hamiltonian constants areg=2.00±0.01,B20=(163±3)·10−4 cm−1,B22=(159±3)·10−4 cm−1,A=−(75±1)·10−4 cm−1. The effect of the invariance in temperature of the resonance magnetic fields in the narrow temperature rangeT=337–340 K and the model of the paramagnetic centre are discussed. According to EPR data a phase transition occurs atT=337 K. This transition from the paraelectric phase to the ferroelectric one is accompanied by a dramatic change in value of the spin-Hamiltonian constantB20.

The site and pseudodonor character of manganese in single-crystal lead telluride

From the analysis of electron paramagnetic resonance (EPR) spectra and the electrical characteristics of as-grown, long-period 'annealed' at room temperature and laser annealed PbTe:Mn single crystals with Mn content NMN approximately=2-7*1018 cm-3 the authors infer that Mn2+ ions in as-grown crystals are incorporated partly interstitially and partly in the metal sublattice sites. In crystals with NMn>or approximately=2*1019 cm-3 Mn ions tend to form clusters. In such cases manganese behaves as an amphoteric impurity, as a small amount of Mn ions in the metal sublattice points cannot compensate for the large number of Pb vacancies (NPb approximately 5*1019 cm-3) that act as acceptors. When creating the conditions that promote migration of Mn ions into PbTe metal sublattice points (long-period 'annealing' at T=300 K, IR laser annealing) which is tested by hyperfine structure and superhyperfine structure of EPR spectra, the Mn2+ ions act as pseudodonors, compensating for two holes from each lead vacancy. The electron concentration in such a case is attributed to Te vacancies, which are donors. The spin-Hamiltonian constants were determined at T=20 K for as-grown, long-period 'annealed' and laser annealed PbTe:Mn crystals.

ESR Studies on [Cu(dpt)en](BØ4)2

ESR studies on the title complex revealed the existence of two crystallographically inequivalent molecules in the unit cell. The temperature variation of spin-Hamiltonian constants is indicating that the geometry around copper (II) is mainly square pyramidal with trigonal bipyramidal distortion at 300 K and this distortion is reduced at 77 K indicating the presence of second order Jahn-Teller distortion. The ground state wave functions of copper (II) at both the temperatures are evaluated.

EPR Spectra and covalency of bis(amidinourea/ O-alkyl-1-amidinourea)copper(II) complexes Part II. Properties of the CuN 42− chromophore

EPR and optical absorption studies have been made on some square planar pink CuN 4 2− chromophore complexes, viz. bis(amidinourea/ O-isopropyl-1- amidinourea/ O-ethoxyethyl-1-amidinourea/ O-methoxyethyl- 1-amidinourea)copper(II) complexes, in the solid state and in different solvents (water, DMF and DMSO) to investigate solute-solvent interaction, if any; spin-Hamiltonian constants of the copper(II) ion; metal-ligand bond parameters; and the environment around the copper(II) ion. In an aqueous medium nine nitrogen superfine lines on the high field 3/2 ↔ 3/2 copper hyperfine splitting component is indicative of four equivalent or nearly equivalent nitrogen atoms surrounding the copper(II) ion. The spectra obtained from different media permitted calculation of the degree of covalence of σ- and π-bonds of the copper(II) ion with the four nitrogen atoms of the ligands. The metal-ligand covalency in these compounds is comparable to that found in copper(II) phthalocyanine and porphine complexes. The covalency of the bis(ligand)copper(II) complexes is attributed to the strong σ-interaction of the copper(II) ion with a deprotonated imino ligand bonding site, and electron delocalization occurs throughout the entire chelate ring.

Electron paramagnetic resonance of Mn 4+ in BaTiO 3

The Electron Paramagnetic Resonance (EPR) of Mn 4+ in the rhombohedral low- temperature phase of BaTiO 3 has been observed at 19.3 and 13.0 GHz. The spectra have axial symmetry along 〈111〉 directions. Intensity measurements prove that the Mn 4+ EPR reflects {111} domain orientation. The spin-Hamiltonian constants are g ‖=1.9968(19), g ‖=2.0015(5), A ‖=67.48(5)×10 −4 cm −1, A ‖=73.04(15)×10 −4cm −1, and D=0.65(1)cm −1 at 4.2 K. The very large D value is more than 20 times that found for the isoelectronic Cr 3+. The latter ion remains centered in its surrounding octahedral oxygen cage, whereas the Mn 4+ is off-center with similar coordinates as Ti 4+. This result is deduced from a superposition-model analysis.

Electron spin resonance and ultrasonically modulated electron spin resonance of Cr3+ions in Ca3Ga2Ge3O12garnet

The spin-Hamiltonian constants and strain-dependent line shift of ESR transitions in Cr3+-doped Ca3Ga2Ge3O12 garnet have been obtained by means of EST and ultrasonically modulated ESR (UMESR) methods. The crystal-field parameters that appear in the spin Hamiltonian for Cr3+ in a trigonal environment are: g/sub ///=1.969+or-0.002, gperpendicular to =1.973+or-0.002 and D=16.201+or-0.005 GHz. The values of some linear combinations of fourth-rank magneto-elastic G tensors of the single Cr3+ ion are calculated.