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  1. 36 Acta Physica Polonica A

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  1. 11 Kamieniarz G.

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1
Content available remote

Quantum Cellular Automata: a Short Overview of Molecular Problem

100%
Tsukerblat B., Palii A., Clemente-Juan J., Suaud N., Coronado E.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
329-335
EN
In this article we summarize the study of the electronic states and electron-vibrational interactions in square-planar molecular entities playing the role of molecular cells in quantum cellular automata (QCA), a promising paradigm of quantum computing. The following issues are shortly discussed: 1) QCA as a paradigm of quantum computing; 2) molecular implementation of QCA; 3) vibronic coupling as the origin of charge trapping, encoding of binary information 4) non-linear cell-cell response; 4) spin-switching in molecular QCA based on mixed-valence cells; 5) multimode dynamic vibronic problem, the symmetry assisted approach.
2
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Dynamical Aspects of Magnetic Switching in a Single Molecule-Based Spin Valve

100%
Płomińska A., Misiorny M., Weymann I.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
555-557
EN
The dynamics of the current-induced magnetic switching process is theoretically studied in a spin-valve device containing a single magnetic molecule of spin S=1. The analysis is performed by using the real-time diagrammatic technique in the sequential electron tunneling regime. In particular, we show that the magnetic moment of a molecule can be reversed also in the presence of intrinsic spin relaxation processes. Moreover, we discuss how the process of magnetic switching depends on a transport bias voltage as well as on some key parameters of the device.
3
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Magnetic Liquid Crystals for Molecular Spintronics

100%
Szczytko J., Budzowski P., Turski H., Witek B., Twardowski A., Glebowska A., Krówczyński A., Pociecha D., Szydlowska J., Górecka E.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1383-1386
EN
The magnetic properties of Ni(II) and Cu(II) complexes were measured. In the case of Ni(II) samples strong enhancement of the magnetic susceptibility below 23 K was observed. The model of structural transition was proposed to explain this behavior.
4
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EPR Spectra of the Genuine-Organic and Metal-Organic TCNQ-Based Anion Radical Salts

100%
Botko M., Čižmár E., Kajňaková M., Feher A.
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vol. 126
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issue 1
252-253
EN
We have measured the electron paramagnetic resonance spectra of genuine-organic anion-radical salts [Me-2,6-di-Me-Py](TCNQ)_{2}, [Me-3,5-di-Me-Py](TCNQ)_{2}, [N-Me-OH-Me-Py](TCNQ)_{2}, [N-Et-OH-Me-Py](TCNQ)_{2}, and metal-organic anion-radical salt [Mn-phen_{3}](TCNQ)_{2}·H_{2}O in the temperature range from 2 K to 300 K in the X-band frequency range. A comparison study of the shape of spectra, g-factors and linewidths with respect to the composition and crystal structure of studied compounds is presented. While the genuine-organic anion-radical salts display a typical EPR response originating from TCNQ pairs, the spectra of metal-organic anion-radical salt are dominated by the contribution of transition metal.
5
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Experimental Evidence for Jahn-Teller Transition in a Fe(II)Fe(III) Bimetallic Oxalate

100%
Tang G., He Y., Xu F., Zhang Q.
Acta Physica Polonica A
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2013
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vol. 123
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issue 1
118-120
EN
Bimetallic oxalate {[N-(n-C_4H_9)_4][FeFe(C_2O_4)_3]}_{n} has been investigated by the Mössbauer spectroscopy. The Mössbauer studies confirm that high-spin Fe(III) (S=5/2) and Fe(II) (S=2) ions are present in the compound. These spectra above 60 K consist of three quadrupole doublets, indicating that there are three different Fe sites in the material. The Mössbauer results reveal that spontaneous magnetization of Fe(II) sublattices increases more steeply than that of Fe(III) sublattices as the temperature decreases from T_{C}. Great increase of quadrupole splitting at 50 K provides compelling evidence for the predicted Jahn-Teller transition.
6
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Field-Induced Slow Magnetic Relaxation in Mn₉W₆ Cluster-Based Compound

80%
Konieczny P., Pełka R., Chorazy S., Podgajny R., Sieklucka B., Wasiutyński T.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
884-886
EN
Magnetic measurements of a three-dimensional (3D) molecular magnet built of Mn₉[W(CN)₈]₆ clusters have been carried out to study its static and dynamic properties. Measurements of ac susceptibility in the presence of static magnetic field revealed slow magnetic relaxations. It was found that for the 120 Hz wave frequency the optimal static field which maximizes the imaginary component of the ac susceptibility is about 500 Oe.
7
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Universal Sequence of the Ground States and Energy Level Ordering in Frustrated Antiferromagnetic Rings with a Single Bond Defect

80%
Antkowiak M., Florek W., Kamieniarz G.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
890-892
EN
The universal sequence of the ground states for antiferromagnetic frustrated rings with the odd number of the local spins s and a single bond defect α described by the isotropic Heisenberg Hamiltonian is discussed. The Lieb-Mattis energy level ordering in a pentanuclear ring is revealed and the arising magnetisation steps are demonstrated.
8
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Small Antiferromagnetic Spin Systems: Just beyond the Rotational Band Model

80%
Florek W., Kaliszan L.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
330-332
EN
Two systems of spins s=1/2 with the Heisenberg interactions are investigated: (i) an equilateral trapezoid and (ii) a regular hexagon. Both cases are compared with the corresponding sublattice Hamiltonians to determine splitting and mixing of energy levels with a given total spin of sublattices. It is shown that small modifications of the Hamiltonian parameters may significantly change (magnetic) properties of the eigenstates, especially probability of finding system in a state with determined value of the sublattice total spin.
9
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Isothermal Entropy Change and Adiabatic Change of Temperature of the Antiferromagnetic Spin-1/2 Ising Octahedron and Dodecahedron

80%
Karľová K., Strečka J., Madaras T.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
630-632
EN
The spin-1/2 Ising octahedron and dodecahedron with a unique antiferromagnetic interaction display an outstanding magnetization jump at zero magnetic field, which consequently leads to a giant magnetocaloric effect during the adiabatic demagnetization. In the present work we report temperature dependences of two basic magnetocaloric response functions: the isothermal entropy change and the adiabatic change of temperature. It is shown that the Ising octahedron and dodecahedron generally exhibit a large negative isothermal entropy change upon increase of the magnetic field, which serves in evidence of their cooling performance.
10
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Photo-Induced Relaxation of Magnetization in Molecular Magnet

80%
Zieliński P., Tracz P., Podgajny R., Pełka R., Bałanda M., Wasiutyński T., Sieklucka B.
Acta Physica Polonica A
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2007
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vol. 112
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issue S
S-183-S-188
EN
The experimental study of photo-induced magnetization of hybrid molecular magnet containing cobalt(II) and tungsten(V) magnetic centers bridged by 4,4'-bpy and CN^- is presented. The observed increase in magnetization rate is attributed to the defects due to inter-valence transfer between Co^{II}W^V↔ Co^{III}W^{IV}. The time evolution of magnetization is parameterized by the power law rather than exponential function.
11
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Magnetic Systems at Criticality: Different Signatures of Scaling

80%
Pełka R., Konieczny P., Fitta M., Czapla M., Zieliński P., Bałanda M., Wasiutyński T., Miyazaki Y., Inaba A., Pinkowicz D., Sieklucka B.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
977-989
EN
Different aspects of critical behaviour of magnetic materials are presented and discussed. The scaling ideas are shown to arise in the context of purely magnetic properties as well as in that of thermal properties as demonstrated by magnetocaloric effect or combined scaling of excess entropy and order parameter. Two non-standard approaches to scaling phenomena are described. The presented concepts are exemplified by experimental data gathered on four representatives of molecular magnets.
12
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DFT Study of Octanuclear Molecular Chromium-Based Ring Using New Pseudopotential Parameters

80%
Brzostowski B., Ślusarski T., Kamieniarz G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1115-1117
EN
We present a comprehensive study of magnetic properties of Cr_8F_8(Piv)_{16} molecular ring (in short Cr8) using the package SIESTA with several choices of chromium pseudopotential parameters. We use generalized gradient approximation to investigate properties of Cr8 ring approximated by replacing the pivallic group by H atoms (hydrogen saturation). For different choice of chromium pseudopotential we examine the electronic and magnetic properties of Cr8 molecule. We compare highest occupied molecular orbital and the lowest unoccupied molecular orbital gaps for both spin channels, magnetic moments, and exchange interaction parameter J. The influence of pseudopotential parameters on obtained results is discussed. Finally our results are compared with other theoretical approaches and experimental data.
13
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Effect of Pressure on Magnetic Properties of TM_3[Cr(CN)_6]_2 · nH_2O Nanoparticles

80%
Zentko A., Zentková M., Kavečanský V., Mihalik M., Mitróová Z., Arnold Z., Kamarád J., Cieslar M., Zeleňák V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
489-493
EN
Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn_3[Cr(CN)_6]_2·nH_2O and Ni_3[Cr(CN)_6]_2·nH_2O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature T_C is reduced from T_C = 56 K for Ni-Prussian blue analogues to T_C = 21 K for Ni-nanoparticles system and from T_C = 65 K for Mn-Prussian blue analogues to T_C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetizationμ_s by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T_C for system of Mn-nanoparticles (ΔT_C/Δp = +13 K/GPa) and to only slight decrease in T_C for system of Ni-nanoparticles (ΔT_C/Δp = -3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small.
14
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Highly Degenerated Ground States in Some Rings Modeled by the Ising Spins with Competing Interactions

80%
Florek W., Antkowiak M., Kamieniarz G., Jaśniewicz-Pacer K.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
411-413
EN
We discuss three Ising ring systems with competing interactions which are analogs of quantum systems and we show that they exhibit similar properties. In particular, the archetypal system of three antiferromagnetically coupled spins s has two magnetically degenerated ground states with |M|=s, when 0
15
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^1H NMR on (Ni_xMn_{1-x})_3[Cr(CN)_6]_2 · nH_2O

80%
Bokor M., Tompa K., Kiss L., Zentková M., Zentko A., Mihalik M., Maťaš S., Mitróová Z.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
485-488
EN
We report on ^1H NMR of (Ni_xMn_{1-x})3[Cr(CN)_6]_2·15H_2O hexacyanochromates, where x changes from 0 to 1. The decay time constants of the free induction decay signals described by an effective spin-spin relaxation time T_{2eff} obtained from M(t) = M_0 exp(t/T_{2eff}) decrease as the local magnetic moments increase produced by the magnetic transition metal ions at the sites of the resonant ^1H nuclei. The recovery of the magnetization in the spin-lattice relaxation time (T_1) experiments was single-exponential.
16
Content available remote

Collinear and Non-Collinear Configurations in Classical Geometrically Frustrated Ring-Shaped Systems

80%
Grajek M., Kopyciuk T., Florek W., Marlewski A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
417-419
EN
Geometrically frustrated quantum spin systems, with competing antiferromagnetic couplings, show the Kahn degenerate frustration for some specific values of Heisenberg Hamiltonian parameters. It has been recently shown for rings with a defect bond and centered rings. In the case of classical counterparts of these systems, degenerated configurations with the lowest energy are present for the energy function parameter greater than a certain threshold. In these domains such configurations are planar but non-collinear with continuous changes of the net magnetic moment with respect to the Hamiltonian parameter. Outside these domains there is unique collinear ground state configuration (neglecting choice of the net magnetic moment direction). However, these collinear configurations are the same in both non-frustrated and geometrically frustrated domains. Numerically exact calculations for quantum systems strongly confirm that determined properties of their classical counterparts realize the classical limit s→∞.
17
Content available remote

Frustration Measure for Molecular Magnets with Single-Ion Anisotropy

80%
Kozłowski P.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
423-425
EN
The universal frustration measure and its extension to anisotropic systems is calculated for a family of spin Hamiltonians modeling a hypothetical ring-shaped chromium-based molecular magnets. The proposed extension takes into account the impact of single-ion anisotropy on the magnetic centers and behaves more consistently with respect to the isotropic counterpart. The influence of anisotropy on both measures is assessed, which leads to a conclusion that frustration decreases with increasing absolute value of single ion anisotropy.
18
Content available remote

Effect of Pressure on Magnetic Properties of Hexacyanochromates

80%
Mitróvá Z., Maťaš S., Mihalik M., Zentková M., Arnold Z., Kamarád J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
469-472
EN
We present the study of pressure effect on magnetic properties of TM^{2+}_3[Cr^{III}(CN)_6]_2·nH_2O ferrimagnets and ferromagnets (TM = Cr and Co) under pressures up to 0.9 GPa. Applied pressure strengthens super-exchange interaction in Cr^{2+}-prussian blue analogues with dominant antiferromagnetic interaction J_{AF} leading to increase in the Curie temperature T_C (ΔT_c/Δp = 29.0 K/GPa) and reduces T_C of Co^{2+}-prussian blue analogues with dominant ferromagnetic interaction J_F (ΔT_c/Δp = -1.8 K/GPa). The rise of J_{AF} interaction is attributed to the enhanced value of the single electron overlapping integral S. On the other hand, the applied pressure slightly affects bonding angles between magnetic ions mediated by the cyano-bridge and reduces the strength of magnetic coupling. Changes of the magnetization curve with pressure can be attributed to changes of magnetic anisotropy. The reduction of magnetization with pressure observed on Cr^{2+}-prussian blue analogues can be explained by pressure induced transition from Cr^{2+} high spin state to Cr^{2+} low spin state. All pressure induced changes are reversible.
19
Content available remote

Magnetic Properties of an S=2 Ladder Spin Model Applied to a New Quasi-One-Dimensional Magnet [Mn(phen)_{3}](TCNQ)_{2}·H_{2}O

80%
Botko M., Cheranovskii V., Vasilets G., Čižmar E., Kajňaková M., Anders A., Starodub V., Feher A.
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vol. 126
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issue 1
20-21
EN
The effective spin S=2 Heisenberg ladder model with free-spin admixtures was proposed for the study of the low-temperature magnetic properties of the complex compound [Mn(phen)_{3}](TCNQ)_{2}·H_{2}O. The temperature dependence of magnetic susceptibility was found to be close to experimental data.
20
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Spin and Charge Transport in a Magnetic Tunnel Junction with Magnetic Impurities Embedded in the Tunnel Barrier

80%
Misiorny M., Barnaś J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2
196-199
EN
Electronic transport in a nanoscopic magnetic tunnel junction with magnetic particles or magnetic impurity atoms/molecules embedded in the barrier is studied theoretically. The impurity Hamiltonian includes magnetic anisotropy of easy axis type with additional perpendicular term. The description takes into account both elastic tunneling processes as well as inelastic processes associated with a flip of electron spin.
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