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Wyświetlanie 1-11 z 11
Tytuł:
Modeling of the Experimental Molecular-Based Ring-Shaped Nanomagnets
Autorzy:
Antkowiak, M.
Kozłowski, P.
Musiał, G.
Florek, W.
Kamieniarz, G.
Esposito, F.
Powiązania:
https://bibliotekanauki.pl/articles/1534905.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.40.Mg
Opis:
Quantum transfer matrix technique and numerically exact diagonalization method are applied to the Heisenberg spin systems to model ring-shaped molecules. Two cases are investigated: (i) a dozen of S = 1 spins with additional biquadratic exchange and (ii) a dimetallic molecule $Cr_7Cd$, where it is assumed that exchange anisotropy is determined in a local coordination system. In the latter case the calculated susceptibility is compared with experimental results.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 965-966
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
KEr(MoO$\text{}_{4}$)$\text{}_{2}$ and CsDy(MoO$\text{}_{4}$)$\text{}_{2}$ - Low-Dimensional Ising Magnets
Autorzy:
Kačmár, M.
Orendáčová, A.
Čizmár, E.
Horváth, D.
Orendáč, M.
Bondarenko, V.
Anders, A. G.
Feher, A.
Jaščur, M.
Powiązania:
https://bibliotekanauki.pl/articles/2013657.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.10.Hk
75.40.Mg
Opis:
In the present work the behaviour of cluster excitations in magnetic field, B, parallel to the easy axis was experimentally studied by the measurements of KEr(MoO$\text{}_{4}$)$\text{}_{2}$ and CsDy(MoO$\text{}_{4}$)$\text{}_{2}$ specific heat, C, vs. B dependence studied at a constant temperature. Corresponding Monte Carlo simulations of C revealed that despite of the fact that the Ising exchange-coupling models proved useful for a sufficient description of the specific heat of these dipolar systems in B=0, the analysis of current experimental data requires a partial renormalization of exchange-coupling constants previously obtained from B=0 analysis. The influence of crystal field effects and long-range character of spin correlations is discussed.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 807-810
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Susceptibility Behaviour of CuGeO$\text{}_{3}$: Comparison between Experiment and the Quantum Transfer Matrix Approach
Autorzy:
Bieliński, M.
Renard, J.-P.
Powiązania:
https://bibliotekanauki.pl/articles/2013702.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
Thermodynamical properties of one-dimensional S=1/2 Heisenberg model with dimerized nearest- and uniform next-nearest-neighbour interactions are studied by the numerically exact quantum transfer matrix method and the results are applied to CuGeO$\text{}_{3}$. Suzuki-Trotter formula is used to obtain a classical system with spin σ=3/2 and effective interactions between nearest-neigbours only. Magnetic susceptibility curve is calculated and compared with new experimental results performed in a wide temperature range, revealing the presence of frustration in the model proposed for CuGeO$\text{}_{3}$.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 851-854
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Transfer-Matrix Simulations of Linear Magnetic Systems
Autorzy:
Matysiak, R.
Caramico D'Auria, A.
Esposito, F.
Esposito, U.
Powiązania:
https://bibliotekanauki.pl/articles/2013975.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
The quantum transfer-matrix method was applied to study the finite-temperature static properties of the spin S=1 antiferromagnetic Heisenberg chains in a wide range of the single-ion anisotropy and temperatures. The high-resolution quantum transfer-matrix simulation data are obtained for the zero-field susceptibility, specific heat as well as for the field-dependent magnetization. The microscopic parameters of a number of real quasi-one-dimensional compounds are found from fitting procedures, some theoretical approaches are numerically verified and an extension of the technique to a non-uniform bond alternating molecular magnets is also put forward.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 959-962
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:
Field-Dependent Specific Heat and Energy Gap in the $Yb_4As_3$ Compound
Autorzy:
Matysiak, R.
Powiązania:
https://bibliotekanauki.pl/articles/1534925.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.40.Cx
75.40.Mg
71.55.Ak
Opis:
We report the low-temperature specific-heat simulation results and reanalyzed measurement data on polydomain $Yb_4As_3$ in magnetic fields B = 0 and 6 T. The data considered here are independent and supplement those considered earlier. A quantitative agreement has again been achieved between the magnetic experimental specific-heat data and the numerical results obtained by the quantum transfer-matrix simulation technique, yielding a new evidence in favour of the Heisenberg model of the antiferromagnetic spin S = 1/2 chain with the value of the exchange integral $J//k_{B}$ = - 28 K. The finite-size quantum transfer matrix approximants have been extrapolated exploiting the procedure developed previously. On the basis of the data in magnetic field and using the corresponding density-matrix renormalization group results, the energy-gap size Δ has been estimated for the applied magnetic field B = 6 T, leading to the experimental verification in the extended region of the scaling law Δ ∿ $B^{2//3}$ following from the sine-Gordon model.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 969-970
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Finite-Size Scaling Study of Five-Dimensional Ising Model
Autorzy:
Merdan, Z.
Aras, N.
Kürkçü, C.
Powiązania:
https://bibliotekanauki.pl/articles/1398913.pdf
Data publikacji:
2016-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
64.60.Cn
75.40.Cx
75.40.Mg
Opis:
The five-dimensional ferromagnetic Ising model is simulated on the Creutz cellular automaton algorithm using finite-size lattices with linear dimension 4 ≤ L ≤ 8. The critical temperature value of infinite lattice is found to be $T^{χ}$ (∞=8.7811 (1) using 4 ≤ L ≤ 8 which is also in very good agreement with the precise result. The value of the field critical exponent (δ =3.0067(2)) is good agreement with δ =3 which is obtained from scaling law of Widom. The exponents in the finite-size scaling relations for the magnetic susceptibility and the order parameter at the infinite-lattice critical temperature are computed to be 2.5080 (1), 2.5005 (3) and 1.2501 (1) using 4 ≤ L ≤ 8, respectively, which are in very good agreement with the theoretical predictions of 5/2 and 5/4. The finite-size scaling plots of magnetic susceptibility and the order parameter verify the finite-size scaling relations about the infinite-lattice temperature.
Źródło:
Acta Physica Polonica A; 2016, 129, 6; 1100-1104
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spinodal Decomposition of Magnetic Ions in Eu-Codoped $Ge_{1-x}Cr_{x}Te$
Autorzy:
Podgórni, A.
Kilanski, L.
Dobrowolski, W.
Górska, M.
Reszka, A.
Domukhovski, V.
Kowalski, B.
Brodowska, B.
Anderson, J.
Butch, N.
Slynko, V.
Slynko, E.
Powiązania:
https://bibliotekanauki.pl/articles/1403631.pdf
Data publikacji:
2012-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.80.Ga
75.40.Cx
75.40.Mg
75.50.Pp
Opis:
We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions in the $Ge_{1-x-y}Cr_{x}Eu_{y}Te$ samples with chemical composition varying in the range of 0.015 ≤ x ≤ 0.057 and 0.003 ≤ y ≤ 0.042. The ferromagnetic transition at temperatures 50 ≤ T ≤ 57 K was observed, independent of the chemical composition. The long-range carrier mediated itinerant magnetic interactions seem to be responsible for the observed ferromagnetic order. The magnetic irreversibility with coercive field $H_C$ = 5 - 63 mT and the saturation magnetization $M_S$ ≈ 2 - 6 emu/g are found to strongly depend on the chemical composition of the alloy.
Źródło:
Acta Physica Polonica A; 2012, 122, 6; 1012-1015
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Non-Ising Phase Transitions in the 3D Standard Ashkin-Teller Model
Autorzy:
Jeziorek-Knioła, D.
Musiał, G.
Dębski, L.
Rogiers, J.
Dylak, S.
Powiązania:
https://bibliotekanauki.pl/articles/1427129.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Hk
75.30.Kz
75.40.Cx
75.40.Mg
Opis:
The phase transition line near the Ising point region is studied for the 3D standard Ashkin-Teller model on a cubic lattice. This model with a multicomponent order parameter is one of the important reference points in statistical physics since it shows an interesting and complicated phase diagram. The main motivation for our study was nonuniversal behavior suggested for this line. The large-scale Monte Carlo simulations using the Binder and Challa like cumulants are performed. Accurate analysis to exclude the latent heat inherence is applied. Specific behavior of the Challa like cumulants is discovered and its interpretation is proposed. The paper is closed with preliminary conclusions concerning the continuous but non-Ising character of these phase transitions in the lower part of the mixed phase region and the possiblity of the first order on the line connecting it to the Ising point.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1105-1107
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:
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
    Wyświetlanie 1-11 z 11

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