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  1. 36 Acta Physica Polonica A

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  1. 11 Kamieniarz G.

  2. 8 Brzostowski B.

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1
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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.
2
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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.
3
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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.
4
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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.
5
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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.
6
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Andreev Transport through a Magnetic Molecule Weakly Coupled to Ferromagnetic Leads

80%
Pawlicki F., Weymann I.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
594-596
EN
The Andreev transport through a single molecular magnet coupled to two external ferromagnetic leads and one superconducting electrode is studied theoretically by means of the real-time diagrammatic technique. The calculations are performed by including the sequential tunneling processes between the molecule and ferromagnetic leads, while the coupling to superconductor can be arbitrary. We analyze the dependence of the Andreev current and tunnel magnetoresistance on various intrinsic parameters of the molecule. The superconducting proximity effect results in the formation of molecular Andreev bound states. We show that the transport behavior depends greatly on the type of internal exchange interaction of the molecule, which can lead to corresponding sign changes of the tunnel magnetoresistance of the device.
7
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Spin-Dependent Transport through a Single-Wall Carbon Nanotube Quantum Dot with an S=1 Molecule

80%
Płomińska A., Weymann I.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
475-477
EN
Transport properties of an S=1 molecule attached to a single-wall carbon nanotube quantum dot, which is coupled to two external ferromagnetic leads, are analyzed in the sequential tunneling regime. The magnetizations of the leads are assumed to form either a parallel or an antiparallel magnetic configuration. The calculations are performed by using the real-time diagrammatic technique in the lowest order perturbation theory with respect to the tunnel coupling. It is shown that the presence of the molecule strongly affects the bias voltage dependence of the current and differential conductance in both magnetic configurations, as well as the resulting tunnel magnetoresistance. Negative (greatly enhanced) tunnel magnetoresistance is found in the case of antiferromagnetic (ferromagnetic) coupling between the nanotube and molecule.
8
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DMRG Approach to a Molecular-Based Bimetallic Chain Containing Re(IV) and Cu(II) Ions

80%
Sobczak P., Barasiński A., Matysiak R., Drzewiński A., Kamieniarz G., Bieńko A., Mroziński J.
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issue 5
975-977
EN
The bimetallic chain complex [Cu(tren)]ReCl_6 is numerically analysed on the basis of the anisotropic quantum Heisenberg model without the mean-field corrections by the density-matrix renormalization group approach. The high accuracy results of our simulations have been fitted to the corresponding experimental susceptibility data above the crossover regime. The set of model parameters comprising the strength of antiferromagnetic couplings, the single-ion anisotropy term and the corresponding g factors have been found: J/k_{B} = 3.5 ± 0.5 K, D/k_{B} = 35 ± 5 K, g_{Cu} = 2.07 ± 0.05 and g_{Re} = 1.73 ± 0.01.
9
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Application of the Package SIESTA to Linear Models of a Molecular Chromium-Based Ring

80%
Ślusarski T., Brzostowski B., Tomecka D., Kamieniarz G.
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issue 5
967-968
EN
We investigate for the first time the electronic and magnetic properties of the linear models of Cr_8F_8(Piv)_{16} molecular ring using the SIESTA package. In the first step the proper values of the SIESTA parameters and the optimal basis set needed for the convergence of the total energy are established. Next the estimates of the magnetic coupling J confirming the previous density functional theory calculations are presented.
10
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First Principles Calculation of ε-Phase of Solid Oxygen

80%
Kamaruddin K., Abedin A., Zabidi N., Yahya M., Taib M., Rosli A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
468-471
EN
The electronic structures of ε-phase of solid oxygen (O₂)₄ are studied within the framework of density-functional theory. The intriguing molecule has been known to have magnetic properties at room temperature by applying pressure. Nevertheless, until now there was no evidence of band structure studied in the antiferromagnetic behaviour of (O₂)₄. We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O₂)₄ could not be seen experimentally, and antiferromagnetic configuration of (O₂)₄ was seen at higher pressure of about 10 GPa. The antiferromagnetic state transforms into the superconducting state as the sample temperature decreases. The results can serve as a useful approximation in studying general features of the electronic structure. The (O₂)₄ clusters are reported in the Raman study, having significant absorption at 1516 cm¯¹ below infrared region.
11
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Spin-Peierls Transition in (N-Me-Tetra-Me-Pz)(TCNQ)_{2}

80%
Kajňaková M., Botko M., Starodub V., Čižmár E., Feher A.
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vol. 126
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issue 1
254-255
EN
The new organic anion-radical salt (N-Me-Tetra-Me-Pz)(TCNQ)_{2}, (Pz = pyrazine) was studied as a low dimensional magnetic system. Heat capacity and EPR studies were performed in the temperature range from 2 to 300 K. The magnetic susceptibility was measured in the temperature range from 2 to 300 K and in magnetic fields of 100 mT and 1 T. The magnetic properties of this new system can be described as a dimerized Heisenberg spin S=1/2 chain possessing a spin-Peierls transition at 42 K.
12
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Magnetic Properties of Transition Metal Molybdates

80%
Konieczny P., Pełka R., Grzesiak-Nowak M., Szymańska A., Łasocha W., Wasiutyński T.
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vol. 126
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issue 1
250-251
EN
Two examples of transition metal molybdates were studied with the use of X-ray diffraction and DC magnetometry techniques. First compound, copper dimolybdate trihydrate CuMo_{2}O_{7}·3H_{2}O contains 2D layers. The second one is fibrillar cobalt trimolybdate octahydrate CoMo_{3}O_{10}·8H_{2}O. Both compounds exhibit paramagnetic behaviour at room temperature. However, in the first one copper ions form dimers linked by oxygen bridges, in which exchange interactions between two localized spin states occur. The second compound consists of isolated cobalt ions in the octahedral surroundings, resulting in magnetic properties deviating from the Curie law.
13
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DFT and Falicov-Kimball Model Approach to Cr_{9} Molecular Ring

80%
Brzostowski B., Wojciechowski M., Lemański R., Kamieniarz G., Timco G., Tuna F., Winpenny R.
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vol. 126
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issue 1
270-271
EN
Based on density functional theory (DFT) calculations, we present electronic and magnetic properties of nanometallic homo-nuclear chromium-based molecular rings Cr_{9}F_{9}Cl_{2}(O_{2}C-C(CH_{3})_{3})_{17} recently synthesized. The magnetic moments are calculated, the spin density maps are discussed and the exchange interaction parameter is extracted. The complementary studies are carried out using the Falicov-Kimball model which reproduces very well the energy levels determined by different magnetic broken symmetry configurations obtained by DFT.
14
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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.
15
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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.
16
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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.
17
Content available remote

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.
18
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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.
19
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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.
20
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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.
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