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Wyświetlanie 1-15 z 17
Tytuł:
Universal Sequence of the Ground States and Energy Level Ordering in Frustrated Antiferromagnetic Rings with a Single Bond Defect
Autorzy:
Antkowiak, M.
Florek, W.
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1032629.pdf
Data publikacji:
2017-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.10.Hk
75.50.Xx
03.65.Aa
Opis:
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.
Źródło:
Acta Physica Polonica A; 2017, 131, 4; 890-892
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Anisotropy, Geometric Structure and Frustration Effects in Molecule-Based Nanomagnets
Autorzy:
Kamieniarz, G.
Kozłowski, P.
Antkowiak, M.
Sobczak, P.
Ślusarski, T.
Tomecka, D.
Barasiński, A.
Brzostowski, B.
Drzewiński, A.
Bieńko, A.
Mroziński, J.
Powiązania:
https://bibliotekanauki.pl/articles/1426672.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Xx
75.10.Jm
75.10.Pq
75.40.Cx
Opis:
In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n → ∞) frustration can be considered as the opposite to bipartiteness in the odd numbered (3 ≤ n ≤ 9) s = 3/2 quantum spin rings. We analyse the influence of exchange interactions and anisotropy on magnetic susceptibility of bimetallic (S = 3/2, s = 1/2) chains composed of Cu ions linked to different 3d ions by fitting experimental data. We reach the remarkable consistency of the density functional theory estimates of the magnetic couplings in $Cr_8$ molecule and provide strong support to the spin models exploited in the literature.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 992-998
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quantum Effects and Critical Behavior in Low-Dimensional Spin-1/2 Systems
Autorzy:
Kamieniarz, G.
Musial, G.
Dębski, L.
Bieliński, M.
Dekeyser, R.
Powiązania:
https://bibliotekanauki.pl/articles/1964803.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Mg
64.60.-i
75.10.Hk
75.10.Jm
Opis:
The critical coupling and spontaneous magnetization curve for the 2D-Ising model are calculated using the effective-field method with correlations. An application of the method to the quantum S=1/2 1D-Heisenberg model is presented and reliable low-temperature estimates of the specific heat are evaluated.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 445-447
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effective Field Methods for Magnetic Systems
Autorzy:
Kamieniarz, G.
Dekeyser, R.
Musiał, G.
Powiązania:
https://bibliotekanauki.pl/articles/1930600.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.Cn
64.60.Fr
05.50.+q
75.10.Dg
75.10.Hk
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
The self-consistency conditions inherent in the mean-field approximation are extended to take into account some pair correlations. Ii is shown that this extension is systematically improvable and applicable to the spin systems with short-range interactions in the entire temperature region. With two correlations included and the renormalization-group ideas implemented, the critical properties of the Ising model are satisfactorily revealed. Moreover, the improved estimates of the thermodynamical quantities for the quantum linear XY model from the finite-size calculations are found down to very low temperatures.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 413-417
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Direct Simulations of the Quantum Model for CsNiF$\text{}_{3}$
Autorzy:
Caramico D'Auria, A.
Esposito, F.
Esposito, U.
Kamieniarz, G.
Dekeyser, R.
Powiązania:
https://bibliotekanauki.pl/articles/1930597.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.Cn
75.10.Dg
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
We address the problem of reliability of a finite-chain technique for CsNiF$\text{}_{3}$. We investigate the effect of the boundary conditions, completely neglected so far, and apply a new extrapolation procedure appropriate for quantities showing non-monotonic behaviour. From a detailed analysis of the specific heat existing theoretical estimates for the model parameters are discriminated and a strong evidence for the reliability of the direct finite-chain technique predictions is presented.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 409-412
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Zero Temperature Magnetic Frustration in Nona-Membered s=3/2 Spin Rings with Bond Defect
Autorzy:
Antkowiak, M.
Kozłowski, P.
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1427128.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.10.Jm
Opis:
Zero-temperature limits of the local and global thermodynamic quantities in the nine-membered antiferromagnetic s=3/2 spin ring are investigated by means of numerical exact diagonalization. An anisotropic Heisenberg model with tunable bond defect reflecting continuously varying topology (from closed to open ring) is exploited. The frustrated and non-frustrated phases are identified in the ground-state phase diagram determined by a bond-defect strength and magnetic field. Near the phase boundaries significance of the thermal fluctuations affecting the estimates of the local magnetic quantities found earlier at T=1 K is revealed. For the global quantities the effects of thermal fluctuations are found much weaker. A sequence of the local magnetic moments is analysed and their experimental verification at the edges of the non-frustrated and within the entire frustrated phase is suggested at sufficiently low temperature.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1102-1104
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Highly Degenerated Ground States in Some Rings Modeled by the Ising Spins with Competing Interactions
Autorzy:
Florek, W.
Antkowiak, M.
Kamieniarz, G.
Jaśniewicz-Pacer, K.
Powiązania:
https://bibliotekanauki.pl/articles/1030746.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.50.Ee
75.50.Xx
Opis:
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
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 411-413
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
DMRG Approach to a Molecular-Based Bimetallic Chain Containing Re(IV) and Cu(II) Ions
Autorzy:
Sobczak, P.
Barasiński, A.
Matysiak, R.
Drzewiński, A.
Kamieniarz, G.
Bieńko, A.
Mroziński, J.
Powiązania:
https://bibliotekanauki.pl/articles/1534998.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Xx
75.10.Jm
02.70.Rr
Opis:
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.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 975-977
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical Simulations of Linear S=1 Ferro- and Antiferromagnets
Autorzy:
Kamieniarz, G.
Matysiak, R.
Caramico D'Auria, A.
Esposito, F.
Esposito, U.
Powiązania:
https://bibliotekanauki.pl/articles/1964696.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
75.10.Hk
75.40.Mg
Opis:
The finite-temperature static properties of the spin S=1 antiferromagnetic Heisenberg chains are extensively simulated using the quantum transfer matrix method. The zero-field susceptibility and specific heat as well as the field-dependent magnetization data are evaluated to select the microscopic parameters of a number of real quasi-one-dimensional compounds and to verify some theoretical approaches.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 387-389
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Improved Phase Diagrams of Ashkin-Teller Model
Autorzy:
Pawlicki, P.
Kamieniarz, G.
Kozlowski, P.
Dekeyser, R.
Rogiers, J.
Powiązania:
https://bibliotekanauki.pl/articles/1964805.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Mg
75.10.Hk
64.60.Ak
Opis:
The phase diagram of the Askhin-Teller model in two dimensions is determined. Numerical calculations are performed for the simple square L × L lattice using transfer matrix technique. Exploiting finite-size scaling all unknown critical lines were obtained with good accuracy. An extended version of the Ashkin-Teller model is also considered within the molecular field renormalization group method and the critical surface for three-parameter odd-parity Hamiltonian is calculated.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 453-456
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Fundamental Gaps in $Cr_{8}$, $Cr_{7}Ni$ and $Cr_{7}Cd$ Molecules
Autorzy:
Brzostowski, B.
Wojciechowski, M.
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1368520.pdf
Data publikacji:
2014-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.15.Mb
31.15.E-
71.10.-w
Opis:
In this paper we investigate fundamental gaps of three octametallic Cr-based molecular rings $Cr_{8}F_{8}(Piv)_{16}$, $Cr_{7}NiF_{8}(Piv)_{16}$ and $Cr_{7}CdF_{8}(Piv)_{16}$ using the SIESTA package. We find that for the ground-state antiferromagnetic configurations, the gap of the homometallic ring is significantly higher than those of the heterometallic rings. In addition, the HOMO and LUMO orbitals are plotted and discussed.
Źródło:
Acta Physica Polonica A; 2014, 126, 1; 234-235
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Time Evolution of the Magnetic Chains with Uniaxial Anisotropy
Autorzy:
Woźniak, D.
Drzewiński, A.
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1385537.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
76.60.Es
05.30.-d
Opis:
In the framework of the matrix product states representation the effect of the single-ion anisotropy on the time evolution of the initial state after a sudden quench of the local magnetic field has been investigated. The overlap of the initial and time-evolved states, so called the Loschmidt echo, magnetization profiles and correlation functions are presented.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 333-335
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some Mesoscopic Rings: Exact Simulations and Experiment
Autorzy:
Kamieniarz, G.
Matysiak, R.
Caramico D'Auria, A.
Esposito, F.
Benelli, C.
Powiązania:
https://bibliotekanauki.pl/articles/2014557.pdf
Data publikacji:
2000-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Mg
75.40.Cx
75.10.Jm
Opis:
A numerical transfer-matrix approach and an exact diagonalization technique exploiting the point-group symmetry are worked out in the framework of quantum statistical mechanics and group theory for finite rings. They are applied to spin models of the high nuclearity cyclic clusters [Mn(hfac)$\text{}_{2}$NITPh]$\text{}_{6}$ and Ni$\text{}_{12}$(O$\text{}_{2}$CMe)$\text{}_{12}$(chp)$\text{}_{12}$(H$\text{}_{2}$O)$\text{}_{6}$(THF)$\text{}_{6}$. The microscopic parameters of both molecules (J/k$\text{}_{B}$=350±10 K and J/k$\text{}_{B}$=8.5 K±0.5, g=2.23±0.01, respectively) are then obtained from a fit of the theoretical susceptibility curves to the experimental results which are supplemented for Ni$\text{}_{12}$ by new low-temperature measurements.
Źródło:
Acta Physica Polonica A; 2000, 98, 6; 721-727
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical Test of Molecular-Field Renormalization Group
Autorzy:
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1964785.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Mg
75.10.Im
64.60.Ak
Opis:
A new transfer matrix approach has been worked out to test the predictions of the molecular-field renormalization group for square Ising clusters with a linear size up to L ≤ 11. The convergence of the finite-size critical couplings towards the exact value for the molecular-field renormalization group is shown and the limit of the ratio y$\text{}_{h}$/y$\text{}_{t}$ consistent with the corresponding universal value is revealed.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 423-426
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Relaxation dynamics in the spin-1 Heisenberg antiferromagnetic chain after a quantum quench of the uniaxial anisotropy
Autorzy:
Woźniak, D.
Drzewiński, A.
Kamieniarz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1058535.pdf
Data publikacji:
2016-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
76.60.Es
05.30.-d
75.30.Gw
Opis:
In the framework of the matrix product state representation the effect of a sudden turning on of the uniaxial anisotropy on the time evolution of the Haldane state has been investigated. Depending on the value of the uniaxial anisotropy parameter, the calculations were derived within (or outside) the region where the Haldane gap survives. An exact expression for the time evolution of the Loschmidt echo has been derived and, moreover, its collapse and revival behaviour was captured. In addition, the non-local order parameter of a time evolving state was tracked, revealing two types of relaxations.
Źródło:
Acta Physica Polonica A; 2016, 130, 6; 1395-1400
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 17

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