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1
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Transfer-Matrix Simulations of Linear Magnetic Systems

100%
Matysiak R., Caramico D'Auria A., Esposito F., Esposito U.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
959-962
EN
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.
2
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Numerical Simulations of Linear S=1 Ferro- and Antiferromagnets

88%
Kamieniarz G., Matysiak R., Caramico D'Auria A., Esposito F., Esposito U.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
387-389
EN
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.
3
Content available remote

Some Mesoscopic Rings: Exact Simulations and Experiment

88%
Kamieniarz G., Matysiak R., D'Auria A. C., Esposito F., Benelli C.
Acta Physica Polonica A
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2000
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vol. 98
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issue 6
721-727
EN
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)_{2}NITPh]_{6} and Ni_{12}(O_{2}CMe)_{12}(chp)_{12}(H_{2}O)_{6}(THF)_{6}. The microscopic parameters of both molecules (J/k_{B}=350±10 K and J/k_{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_{12} by new low-temperature measurements.
4
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Direct Simulations of the Quantum Model for CsNiF_{3}

88%
Caramico D'Auria A., Esposito F., Esposito U., Kamieniarz G., Dekeyser R.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
409-412
EN
We address the problem of reliability of a finite-chain technique for CsNiF_{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.
5
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Modeling of the Experimental Molecular-Based Ring-Shaped Nanomagnets

76%
Antkowiak M., Kozłowski P., Musiał G., Florek W., Kamieniarz G., Esposito F.
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issue 5
965-966
EN
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.
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