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  1. 42 Acta Physica Polonica A

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  1. 5 Avram N.

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1
Content available remote

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

100%
Lulek T.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 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.
2
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Parametrization of the Bilinear Orbit—Lattice Interaction

100%
Pastusiak W.
Acta Physica Polonica A
|
1991
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vol. 80
|
issue 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.
3
Content available remote

Rationalization of Spectra of Rare Earths in Condensed Matter

100%
Reisfeld R., Jørgensen C.
Acta Physica Polonica A
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1993
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vol. 84
|
issue 5
1011-1019
EN
The parametrized models are compared with counter-intuitive consequences of the non-relativistic Schrödinger treatment. For both 4f^{ q}, 5f^{ q} and d^{9} systems in condensed matter, the energy levels must be strongly influenced by correlation effects. The parametrization of intensities is conceptually very different for f^{ q} and d^{9} compounds. The bandwidths of absorption and luminescence are discussed and related to the Born-Oppenheimer factorization.
4
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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
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vol. 90
|
issue 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.
5
Content available remote

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
|
1996
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vol. 89
|
issue 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.
6
Content available remote

Electronic Structure of PrCo_2Ge_2

63%
Diviš M., Vejpravová J., Rusz J., Prokleška J., Sechovský V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 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.
7
Content available remote

Low Temperature Magnetic Ordering in NdAgAl₃

63%
Nallamuthu S., Džubinská A., Reiffers M., Nagalakshmi R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 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
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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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vol. 112
|
issue 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.
9
Content available remote

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

63%
Kripal R., Pandey S.
Acta Physica Polonica A
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2010
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vol. 118
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issue 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.
10
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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
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vol. 119
|
issue 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.
11
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Investigations on the Spin-Hamiltonian Parameters and Local Structure of the Orthorhombic Cu^{2+} Center in PbTiO_3 Crystal

51%
Chao-Ying L., Li-Bin C., Xue-Mei Z.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 6
1671-1675
EN
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.
12
Content available remote

Comparative Study between Energy Levels of Cr^{3+} and Co^{2+} Ions Doped in MgF_{2} Crystal

51%
Nistora R., Andreici L., Avram N.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 4
538-540
EN
The aim of this paper is to present a comparison of the energy level schemes of Cr^{3+} (3d^{3} electrons) and Co^{2+} (3d^{7} electrons), each of ions doped, separately, in MgF_{2} crystal. We report on the detailed and consistent crystal field analysis of Cr^{3+} spectra in MgF_{2} crystal and compare with results, previously obtained, for Co^{2+}, doped in same host matrix. The results are based on application of the exchange charge model of crystal field to the calculation of crystal field parameters and energy levels of both ions doped in MgF_{2}.The calculations have been performed on previously optimized geometry of MgF_{2} crystal. The obtained results are compared with experimental data and discussed.
13
Content available remote

Exchange Charge Model for Fe^{3+}:LiAl_{5}O_{8}

51%
Vaida M., Avram C.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 4
541-543
EN
The aim of this paper is the theoretical investigation of Fe^{3+} doped in the ordered phase of LiAl_{5}O_8. We used the shell model and pair potential approximation to optimize the geometric structure of LiAl_{5}O_{8}. This approach enables the modeling of the crystal field parameters of LiAl_{5}O_8 and then calculates the energy levels scheme of Fe^{3+} ions doped in tetrahedral sites in the title crystal. Consistent crystal field analysis and the energy level splittings for LiAl_{5}O_{8} doped with Fe^{3+} ions was performed in the frame of the exchange charge model of crystal field. The comparison of the theoretically obtained results for energy levels with the experimental data, yields satisfactory agreement and confirms the validity of the exchange charge model.
14
Content available remote

Point-Contact Spectroscopy of Ce_{1-x}RE_{x}Ni_{5} (RE = Pr, Nd)

51%
Kačmárová T., Reiffers M., Garcia Soldevilla J., Goméz Sal J., Espeso J., Blanco J.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 5
795-798
EN
We report on the study of the electron-quasiparticle interaction function in Ce_{1-x}RE_{x} Ni_{5} (RE = Pr, Nd) pseudobinary compounds for x = 0, 0.2, 0.5, 0.8, and 1 measured by means of point-contact spectroscopy. The measured point-contact spectra (d^{2}V/dI^{2} - directly proportional to the electron- quasiparticle interaction function) of the heterocontacts between Ce_{1-x} RE_{x}Ni_{5} and Cu in the ballistic regime are presented.
15
Content available remote

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
|
vol. 127
|
issue 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.
16
Content available remote

Spectroscopic Study of Rare Earth Chromates: Relation to the Structure

51%
Antic-Fidancev E., Lemaitre-Blaise M., Parada C.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 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.
17
Content available remote

Complete Diagonalization Calculation of the Optical and EPR Data for the Tetragonal Cu^{2+} Center in Cu^{2+}-Doped ZnSe Nanocrystals

51%
Wu X.-X., Zheng W.-C.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 3
795-798
EN
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.
18
Content available remote

Crystal Field Analysis of Cr^{3+} Doped SrAl_{2}O_{4} Spinel

51%
Stanciu M., Ciresan M., Avram N.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 4
544-546
EN
The present work is devoted to the crystal field analysis of trivalent chromium doped in SrAl_{2}O_{4} spinel in the frame of the exchange charge model of crystal field. Using the shell model and pair approximation, we optimize the geometric structure of the crystal. The approach enables the modeling of the crystal field parameters and thus calculates the energy level scheme of Cr^{3+} ions in spinel SrAl_{2}O_{4}. The obtained results are compared with experimental data and discussed.
19
Content available remote

Angular Distortion around Cr^{3+} Ions Doped Diammonium Hexaaqua Magnesium Sulphate Single Crystal

51%
Ciresan M., Vaida M., Avram N.
Acta Physica Polonica A
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2007
|
vol. 112
|
issue 5
835-839
EN
The aim of the present study is to explain the local distortion around Cr^{3+} ions doped in the title crystal using the latest experimental data regarding optical and EPR spectra. We calculated g_ǁ, g_⊥, and D spin-Hamiltonian parameter as function of angle between the C_3 axis and metal-ligand chemical bond in local distorted octahedral cluster [CrO_6]^{9-} formed after doped crystal. The method is based on the single spin-orbit coupling parameter model, in the cluster approach using Macfarlane high order perturbation formulae. The results compared with experimental data give a reasonable agreement.
20
Content available remote

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
|
vol. 131
|
issue 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.
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