Wyniki wyszukiwania - Biblioteka Nauki

1

Parametrization of the Bilinear Orbit—Lattice Interaction

100%

Pastusiak W.

Acta Physica Polonica A

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1991

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tom 80

|

nr 1

107-116

EN

A group theoretical parametrization scheme of the bilinear orbit-lattice interaction is presented. Using this scheme a general analytical form of this interaction in the point-charge electrostatic model has been obtained. Based on this general analytical form the second-order parameters of the bilinear orbit-lattice interaction have been calculated for a tetrahedral complex. For cubic complexes a microscopic interpretation of the G-tensor components in the long-wavelength approximation of acoustic waves is given for the first time. The presented scheme of parametrization as well as the method of calculations of the interaction parameters may be extended to other models of the crystal field.

2

Spin-Orbit Coupling for f-Electrons in a Crystalline Field

100%

Lulek T.

Acta Physica Polonica A

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1993

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tom 84

|

nr 5

867-873

EN

The notion of a spin-orbit interaction arises from consideration of dynamics of multielectron atoms, i.e. systems of N electrons in a spherical potential. This notion is essentially a single-particle one. We sketch its origin as a second-order correction when Dirac four-component wave equations for an electron in external electromagnetic fields are simplified to the two-component Pauli spinors. The constraints in spinorial degrees of freedom consist, roughly speaking, in neglecting the small component of the electron four-function. The spin-orbit interaction term serves to compensate effects of the small component. The crystalline field induces some deviations from spherical symmetry of an isolated atom, which yields some modifications of the spherical form of the spin-orbit interaction operator. These modifications can be described in terms of a number of tensor operators adapted to appropriate chains of subgroups of the spherical symmetry group. We present a classification of independent tensor operators and discuss the relevant parameters for f-ions.

3

A Theoretical Analysis of Zero Field Splitting of Mn^{2+} in Ammonium Oxalate Monohydrate

63%

Kripal R. , Pandey S.

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tom 118

|

nr 4

629-632

EN

The superposition model has been used to investigate the substitution of Mn^{2+} in ammonium oxalate monohydrate. The zero field splitting parameters D and E calculated by the superposition model are compared with the experimental values D_{exp} and E_{exp}, respectively, for Mn^{2+} obtained by electron paramagnetic resonance. Both the zero field splitting parameters D and E calculated theoretically are in good agreement with the experimental values D_{exp} and E_{exp}. The result indicates that the Mn^{2+} ion substitutes for the NH_4^{+} ion in ammonium oxalate monohydrate.

4

Crystal Field Theory of Magnetic Behaviour of Er_{2}(SO_{4})_{3}·8H_{2}O

63%

Gupta R. , Ghosh U. , Basu C.

Acta Physica Polonica A

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1996

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tom 89

|

nr 5-6

649-655

EN

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.

5

Crystal Field Analysis of Cr^{3+} Energy Levels in LiGa_5O_8 Spinel

63%

Brik M. , Avram N. , Avram C.

Acta Physica Polonica A

|

2007

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tom 112

|

nr 5

1055-1060

EN

Detailed and consistent crystal field analysis of the LiGa_5O_8:Cr^{3+} absorption spectrum is performed in the present paper by using the exchange charge model of crystal field. We calculate the crystal field parameters from the crystal structure date and diagonalize the crystal field Hamiltonian to obtain the energy level structure of Cr^{3+} ions in LiGa_5O_8. The obtained energy levels and estimated Racah parameters B and C were compared with the experimental spectroscopic data; good agreement was demonstrated.

6

Electronic Structure of Organometallic Complexes of f Elements. Are Molecular Orbital Calculations a Useful Tool for Spectroscopists?

63%

Jank S. , Amberger H.

Acta Physica Polonica A

|

1996

|

tom 90

|

nr 1

21-32

EN

The crystal field parameters of base-free (Me_{3}SiC_{5}H_{4})_{3}Pr, (C_{5}H_{5})_{3}Pr·NCCH_{3}, (C_{5}H_{5})_{3}La(NCCH_{3})_{2}:Pr, [Pr(C_{8}H_{8})]^{+} and Nd[N(SiMe_{3})_{2}]_{3} as model compound for Nd[CH(SiMe_{3})_{2}]_{3} were inserted into the corresponding energy matrices of a model spin-free f^{1} system. Diagonalizing these matrices the crystal field splitting patterns of the f orbitals were calculated. These experimentally based molecular orbital schemes are compared with the results of previous model calculations.

7

Low Temperature Magnetic Ordering in NdAgAl₃

63%

Nallamuthu S. , Džubinská A. , Reiffers M. , Nagalakshmi R.

Acta Physica Polonica A

|

2017

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tom 131

|

nr 4

1015-1017

EN

We present the detailed study of magnetic, thermodynamic, and transport properties of polycrystalline NdAgAl₃. The compound crystallizes in BaNiSn₃-type tetragonal structure with the space group I4mm. Magnetic, heat capacity and transport measurements indicate the possible antiferromagnetic nature of the ordering below 2 K. The compound shows the Schottky anomaly in heat capacity data. Magnetoresistance is negative at low temperature.

8

Electronic Structure of PrCo_2Ge_2

63%

Diviš M. , Vejpravová J. , Rusz J. , Prokleška J. , Sechovský V.

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nr 1

295-298

EN

The intermetallic compound PrCo_2Ge_2 exhibits very interesting physical properties: antiferromagnetism below T_N = 28 K, an order to order transition at T_R = 8 K, a rich magnetic phase diagram, and huge magnetocrystalline anisotropy as observed by recent experiments on a single crystal in a magnetic field up to 14 T. We performed first principles calculations based on the density functional theory. The localized 4f^2 configuration of Pr^{3+} was treated using the open core approximation. The electronic densities of states were obtained and the position of the Fermi level was found. The hybridization between the Co-3d, Pr-5d and Ge-4p states is discussed. The calculated magnetic moment of Co is found to be quite small (m_{Co} < 0.1 μ_B). The first principles calculations of the crystal field interaction were performed as well: the obtained crystal field parameters were used as the starting parameters for further refinement in comparison with experimental data of the magnetic susceptibility and specific heat. The crystal field splitting of the 4f states was determined.

9

Investigations of the Optical and EPR Spectra for Cr^{3+} Ions in Diammonium Hexaaqua Magnesium Sulphate Single Crystal

51%

Wei Q.

|

tom 118

|

nr 4

670-672

EN

The relations between spin-Hamiltonian parameters and local structure around Cr^{3+} in diammonium hexaaqua magnesium sulphate single crystal were established. On the basis of this, the spin-Hamiltonian parameters, optical spectra and the local structure were investigated successfully. The calculated results are in good agreement with experimental data. This shows that the distortion model adopted in this paper is reasonable.

10

Energy Level Scheme of Nd^{3+} Ion in Rare Earth Oxyhalides, REOX (X = F, Cl, and Br)

51%

Beaury L. , Hölsä J. , Korventausta J. , Krupa J. , Lamminmäki R. , Porcher P. , Rahiala H. , Säilynoja E.

Acta Physica Polonica A

|

1996

|

tom 90

|

nr 6

1203-1213

EN

The energy level schemes of the neodymium oxyhalides (NdOX, X = F, Cl, and Br) were studied and simulated with a phenomenological model accounting simultaneously for both the free ion interactions and the crystal field effect. The former included the electrostatic and interconfigurational interactions as well as the spin-orbit coupling. The simulations were carried out by using the data from the optical absorption and luminescence as well as the inelastic neutron scattering measured at low temperatures between 2.5 and 77 K. The values of the Slater integral F^{2} describing the electrostatic interactions decrease while F^{4} and F^{6} increase as a function of the ionic radius of the halide anion. The strength of the spin-orbit coupling is quite the same in all three matrices. The crystal field effect - measured as the crystal field strength parameter S - is almost twice as strong in the hexagonal NdOF matrix (650 cm^{-1}) than in the tetragonal NdOCI or NdOBr (367 and 378 cm^{-1}, respectively). Similar evolution was obtained for the short-and mid-range crystal field strengths related to the spatial extension of the interaction.

11

Spin-Spin and Spin-Other-Orbit Interactions of Spin-Hamiltonian Parameters for 3d^{2(8)} Ions in Al_2O_3 Crystals

51%

Wei Q. , Guo L. , Yang Z. , Wei B.

Acta Physica Polonica A

|

2011

|

tom 119

|

nr 6

857-859

EN

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.

12

Experimental Study of the Magnetocaloric Effect in Ni(en)(H₂O)₄SO₄·2H₂O - An S = 1 Molecular Magnet with Easy-Plane Anisotropy

51%

Tarasenko R. , Orendáčová A. , Čižmár E. , Orendáč M. , Potočňák I. , Feher A.

Acta Physica Polonica A

|

2017

|

tom 131

|

nr 4

904-906

EN

Magnetocaloric properties of Ni(en)(H₂O)₄SO₄·2H₂O powder were investigated in temperature range from 2 K to 30 K in magnetic fields up to 7 T using isothermal magnetization measurements. The maximum value of the isothermal entropy change in the field 7 T is about 8 J/(kg K), with a refrigerant capacity of 55 J/kg. Temperature dependence of the isothermal entropy change under different magnetic fields is in good agreement with theoretical predictions from crystal electric field parameters.

13

Research on the Spin-Hamiltonian Parameters and Local Structure for the Tetragonal Mo^{5+} Centers in CaWO_{4} Crystal

51%

Mei Y. , Zheng W. , Wei C.

Acta Physica Polonica A

|

2014

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tom 126

|

nr 6

1275-1279

EN

The spin-Hamiltonian parameters (g factors g_{∥}, g_{⊥} and hyperfine structure constants A_{∥}(A), A_{⊥}(A), A_{∥}(B) and A_{⊥}(B), A(A) and A(B) belonging to isotopes ^{95}Mo^{5+} and ^{97}Mo^{5+}) of Mo^{5+} ion at the tetragonally-compressed tetrahedral W^{6+} site in CaWO_4 crystal are calculated from the high-order perturbation formulae based on the two-mechanism model, where besides the contributions to spin-Hamiltonian parameters due to the crystal-field mechanism concerning the crystal-field excited states in the extensively-applied crystal-field theory, those due to charge-transfer mechanism concerning charge-transfer excited states (which are omitted in crystal-field theory) are included. The calculated results are in reasonable agreement with the experimental values. The calculations show that for the high-valence state d^{n} ions (e. g., Mo^{5+} considered) in crystals, the contributions due to charge-transfer mechanism should be taken into account in the studies of spin-Hamiltonian parameters. The local structure of Mo^{5+} center in CaWO_4 crystal due to the impurity-induced local lattice relaxation is estimated from the calculations. The results are discussed.

14

Spectroscopic Study of Rare Earth Chromates: Relation to the Structure

51%

Antic-Fidancev E. , Lemaitre-Blaise M. , Parada C.

Acta Physica Polonica A

|

1996

|

tom 90

|

nr 1

33-44

EN

The luminescence spectra of the trivalent europium ion embedded in various rare earth chromates were analyzed. The spectroscopic data in most of chromates are in agreement with the structural determination but for some others the discrepancy between two methods is underlined. Energy level schemes were deduced from the experimental emission spectra and the crystal field simulation has been performed. The maximum splitting of the ^{7}F_{1} manifold of the Eu^{3+} ion as a function of N_{v}, the so-called crystal field strength parameter, is given. This allows us to classify the compounds according to their crystal field extent.

15

Point-Contact Spectroscopy of Crystalline Electric Field of Heterocontacts PrB_6 and NdB_6 with Pt

51%

Vasil'ová M. , Pristáš G. , Reiffers M. , Flachbart K. , Rusz J. , Shitsevalova N.

|

nr 1

267-270

EN

Point-contact spectra of single crystals PrB_6 and NdB_6 are presented. We observed maxima connected with crystalline electric field excitations in agreement with previous results for applied voltage V>8 mV. Moreover, we observed maxima at 6 mV (PrB_6) and 3 mV (NdB_6), which are probably connected with phonon modes. Moreover, we observed phonon peak at 10.6 mV in PrB_6. Further measurements in magnetic fields and crystalline electric field calculations are necessary.

16

Explanation of the Optical Spectra and Spin-Hamiltonian Parameters for Nickel(II) in Cadmium Bromide Crystal

51%

Gong J. , Wang L. , Feng W. , Yang X. , Zhang F.

Acta Physica Polonica A

|

2011

|

tom 120

|

nr 3

497-500

EN

Based on crystal- and ligand-field theory, double-spin-orbital coupling approach was used to analyze the crystal-field energy levels and spin-Hamiltonian parameters of Ni^{2+} ion at trigonal site in CdBr_2. The local lattice distortion (Δ R and τ_{Ni^{2+}}) is estimated from the crystal field parameters; the crystal field energy Hamiltonian was diagonalized in the full basis consisting of 45 wave functions of the Ni^{2+} ion. Results of calculations are in good agreement with experimental data. The reasonableness of the theoretical results is discussed.

17

Investigations of the EPR and Optical Spectra for VO^{2+} in C_3H_7NO_2 Powders

51%

Wei Q.

|

tom 117

|

nr 6

962-964

EN

The EPR and optical spectra for VO^{2+} in C_3 H_7 NO_2 powders are calculated from complete diagonalization method and perturbation theory method, respectively. The calculated results are in good agreement with observed values. The negative signs of hyperfine structure constants A_∥ and A_⊥ for VO^{2+} in C_3 H_7 NO_2 powders are also suggested from the calculations.

18

Magnetic Field Induced Slow Magnetic Relaxation in KEr(MoO₄)₂

51%

Tkáč V. , Orendáčová A. , Tarasenko R. , Pajerowski D. , Čižmár E. , Orendáč M. , Anders A. , Meisel M. , Feher A.

Acta Physica Polonica A

|

2015

|

tom 127

|

nr 2

353-355

EN

The spin dynamics of a layered magnetic insulator, KEr(MoO₄)₂, have been investigated in a magnetic field applied along the easy axis at temperatures where the magnetism is dominated by the occupation of a ground doublet. More specifically, the DC magnetization and AC susceptibility were studied in magnetic fields up to 5 T and at temperatures ranging from 1.8 to 20 K. The temperature dependence of the AC susceptibility suggests a slowing down of magnetic relaxation with increasing magnetic field. The magnetic field dependence of the AC susceptibility, studied at nominally 2 K, indicates the presence of low-field, intermediate-field, and high-field regimes characterized by the interplay of internal and external magnetic fields that give rise to different relaxation processes.

19

Investigations of the Optical Band Positions and Spin-Hamiltonian Parameters for the Rhombic VO^{2+} Complex in CsCl Crystal

51%

Fang W. , Zheng W. , Yang D. , Tang H.

Acta Physica Polonica A

|

2014

|

tom 125

|

nr 5

1206-1209

EN

The optical band positions and spin-Hamiltonian parameters (g factors g_{i} and hyperfine structure constants A_{i}, where i=x, y, z) of the rhombic VO^{2+} complex in CsCl crystal are calculated together from two theoretical methods. One is the complete diagonalization (of energy matrix) method and another is the perturbation theory method. The calculated results from the two methods coincide and are in reasonable agreement with the experimental values. So, both methods are effective in the explanations of optical and electron paramagnetic resonance (EPR) data for d^1 ions in crystals. The calculations also suggest that in d^1 rhombic octahedra the ground state is almost a pure | d_{xy} ⟩ state. This point is different from that of conjugate d^9 (e.g., Cu^{2+}) ions in rhombic octahedra where the ground state should be an admixture of ground and first excited states.

20

Implications of Invalid Conversions between Crystal-Field Parameters and Zero-Field Splitting Ones Used in Superposition Model

51%

Rudowicz C. , Karbowiak M.

Acta Physica Polonica A

|

2014

|

tom 125

|

nr 5

1215-1219

EN

The methodology used in recent study of the zero-field splitting parameters of Cr^{3+} ions at various orthorhombic symmetry sites in LiKSO_4 by Pandey and Kripal is critically commented on. We argue that the crystal field parameters, B_{kq}, in the Wybourne notation, which were calculated using the superposition model for Cr^{3+} ions in LiKSO_4, may only be converted into the crystal field parameters in the Stevens notation. Regrettably, the authors have also converted the latter parameters supposedly into the zero-field splitting parameters D and E in the conventional notation. Such direct conversions are fundamentally incorrect and constitute factual invalid usage of the conversion relations between the crystal field (ligand field) parameters and the zero-field splitting ones. The cases of an implied usage of the invalid conversion relations between the crystal field parameters and the zero-field splitting parameters occurring in recent literature are also outlined. Pandey and Kripal have found the zero-field splitting parameters theoretically evaluated in this way to be in good agreement with the experimental values. However, the faulty methodology renders the conclusion that Cr^{3+} ions enter into the LiKSO_4 lattice at the substitutional K^{+} sites unjustified. Several other conceptual problems arising from misinterpretations of the crucial notions identified therein are also discussed and clarified.