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1
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Magnetic Exchange Interactions and Estimation of T_N in CsNiF_3 from First Principles

100%
Legut D., Rusz J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
503-506
EN
The CsNiF_3 has been for long time studied as a prototype of quasi-1D planar ferromagnetic system. At very low temperature the studied system is insulator and therefore the magnetic exchange interactions should decay very rapidly. We treated the magnetic exchange coupling within the Heisenberg model for the nearest neighbor interaction between the anti-ferromagnetically coupled Ni-chains. The influence of up to the second-nearest neighbors on the ferromagnetic exchange coupling along the Ni-chains was determined. The exchange interactions were calculated for the experimental volume by the density functional theory, within the all-electron approach using the local density approximation for the exchange and correlation. The Néel temperature was calculated by means of the mean-field theory and by the random-phase approximation method.
2
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Mechanical Properties of Tetragonal and Orthorhombic Phases of Quasi-One-Dimensional Antiferromagnet KCuF_{3}

100%
Legut D., Wdowik U.
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vol. 126
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issue 1
14-15
EN
The density functional theory was used to calculate the elastic constants for the two tetragonal (a-type) and (d-type), and the orthorhombic structures of KCuF_{3}. Based on the single elastic constants the polycrystalline mechanical properties such as bulk, shear, Young moduli and Poisson ratio using Reuss-Voigt-Hill averaging method were estimated. Furthermore, the sound transverse and longitudional velocities (along the a-axis and c-axis) were calculated and the Debye temperatures were determined for all three investigated phases.
3
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Exchange Interactions in a Low-Dimensional Magnetic System Cu(H_{2}O)_{2}(en)SO_{4}

81%
Sýkora R., Legut D., Wdowik U.
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vol. 126
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issue 1
50-51
EN
We report a theoretical ab-initio investigation of the exchange interaction between Cu atoms in Cu(H_{2}O)_{2}(en)SO_{4}, en=C_{2}H_{8}N_{2}(ethylenediamine), an insulating magnetic material. Unlike previous experimental studies which describe the system as a quasi-two-dimensional antiferromagnet, our results, based on the mapping of the system onto an effective Heisenberg model, suggest a quasi-one-dimensional character of magnetism, with the exchange coupling between the Cu atoms being propagated along a zigzag line, lying in the crystal's bc plane and connecting the Cu atoms through the N atoms. Furthermore, we report the calculated positions of the H atoms that have not been provided in experimental papers.
4
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Optical Properties of a Monoclinic Insulator Cu(H₂O)₂(en)SO₄

81%
Sýkora R., Postava K., Legut D., Tarasenko R.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
469-471
EN
We compare theoretically predicted, by means of ab-initio calculations, dielectric tensor and related experimental values obtained from Mueller-ellipsometry measurements of an insulating monoclinic (optically biaxial) crystal of Cu(H₂O)₂(en)SO₄, en=C₂H₈N₂. We concentrate on the static limit, ω→ 0.
5
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Interference Effects in T-MOKE Spectra of Fe Thin Films at the 3p Edges - Theory and Experiment

52%
Legut D., Tesch M., Oppeneer P., Mertins H., Jansing C., Gilbert M., Gaupp A., Bürgler D., Schneider C.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
466-468
EN
We present combined first-principle calculations and experimental results of the transversal magneto-optical Kerr effect (T-MOKE) of thin Fe films across the 3p edges using linearly polarized synchrotron radiation. We show that the experimental T-MOKE spectra at the 3p edges of Fe exhibit clear signals that are strongly influenced by interference effects. Ab initio calculated T-MOKE asymmetry spectra confirm the importance of interference effects. The comparison of experimental with calculated spectra reveals some differences that we attribute to metal/metal interface roughness that is not taken into account in the calculations.
6
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Experimental Study of the Thermal Transport in CsNiF_3 - An S = 1 Quantum Chain

52%
Tkáč V., Orendáčová A., Orendáč M., Legut D., Tibenská K., Feher A., Poirier M., Meisel M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1098-1101
EN
The heat transport in a single-crystal of CsNiF_3 has been performed in the temperature range from 2 K to 7 K in a zero magnetic field, B = 0, as well as in sufficiently large magnetic fields, B = 6 T and 9 T, inducing the ferromagnetic ground state along the hard c-axis. CsNiF_3 represents an S = 1 quasi-one-dimensional XY ferromagnet with the intra-chain exchange coupling J/k_{B} ≈ 24 K, single-ion anisotropy D/k_{B} ≈ 8 K, and ordering temperature T_{N} = 2.7 K. Comparison of the phonon and magnon velocities suggests that phonons are the main heat carriers in this magnetic insulator. The thermal conductivity in B = 0 was analysed in the frame of a standard Debye model. The temperature dependence of the effective phonon mean free path was calculated from the experimental data, and the enhancement of the phonon mean free path in B ≠ 0 was obtained, indicating that magnons act as scattering centers for phonons.
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