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5 Acta Physica Polonica A

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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

2000

tom 97

nr 5

959-962

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.

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

1997

tom 92

nr 2

387-389

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.

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

1994

tom 85

nr 2

409-412

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.

Some Mesoscopic Rings: Exact Simulations and Experiment

88%

Kamieniarz G. , Matysiak R. , A. Caramico D'Auria , Esposito F. , Benelli C.

Acta Physica Polonica A

2000

tom 98

nr 6

721-727

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.

Modeling of the Experimental Molecular-Based Ring-Shaped Nanomagnets

75%

Antkowiak M. , Kozłowski P. , Musiał G. , Florek W. , Kamieniarz G. , Esposito F.

Acta Physica Polonica A

2010

tom 118

nr 5

965-966

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.