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    Wyświetlanie 1-11 z 11
    Tytuł:
    Small Antiferromagnetic Spin Systems: Just beyond the Rotational Band Model
    Autorzy:
    Florek, W.
    Kaliszan, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/1385535.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.50.Ee
    75.50.Xx
    Opis:
    Two systems of spins s=1/2 with the Heisenberg interactions are investigated: (i) an equilateral trapezoid and (ii) a regular hexagon. Both cases are compared with the corresponding sublattice Hamiltonians to determine splitting and mixing of energy levels with a given total spin of sublattices. It is shown that small modifications of the Hamiltonian parameters may significantly change (magnetic) properties of the eigenstates, especially probability of finding system in a state with determined value of the sublattice total spin.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 330-332
    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:
    Quantum Heisenberg Antiferromagnet on Frustrated Bilayer Lattice in Strong Magnetic Fields
    Autorzy:
    Derzhko, O.
    Krokhmalskii, T.
    Richter, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813782.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.45.+j
    75.50.Ee
    Opis:
    In the present paper we consider the low-temperature thermodynamic properties of the quantum Heisenberg antiferromagnet on the frustrated bilayer lattice in strong magnetic fields.Under certain conditions the isolated localized magnon states (singlets on vertical bonds;simultaneous occupation of neighboring vertical bonds is forbidden) are the ground states which dominate thermodynamics and induce a behavior inherent in the well known model of hard squares on a square lattice.We focus on magnetic properties discussing the magnetization and the susceptibility of the spin model.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 433-436
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Marshall-Peierls Sign Rule in Frustrated Heisenberg Chains
    Autorzy:
    Voigt, A.
    Richter, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2013996.pdf
    Data publikacji:
    2000-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.40.Mg
    75.50.Ee
    Opis:
    We consider the frustrated antiferromagnetic s=1 Heisenberg quantum spin chain with regard to the Marshall-Peierls sign rule. Using exact diagonalization data we investigate the breakdown of the Marshall- Peierls sign rule in dependence on frustration and compare our findings with data for s=1/2. We calculate a critical value of frustration J$\text{}_{2}^{crit}$, where the Marshall-Peierls sign rule is violated. The extrapolation of this value to the infinite chain limit holds J$\text{}_{2}^{crit}$ ≈ 0.016, lower than in the case of s=1/2 (J$\text{}_{2}^{crit}$ ≈ 0.027). T his points to a stronger influence of frustration in the case of s=1. Nevertheless, the calculation of the weight of the Ising-states violating the Marshall- Peierls sign rule shows that the latter holds approximately even for a quite large frustration and may be used for numerical techniques.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 5; 979-982
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Towards Spin-Wave Like Approach to the J-J Heisenberg Antiferromagnet in Terms of Composite Spins
    Autorzy:
    Grzybowski, P.
    Chhajlany, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810417.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.50.Ee
    75.40.Cx
    Opis:
    Conventional spin-wave approach relies on an expansion around a relevant classical (unentangled) ground state or equivalently the ground state in the mean field approximation for the quantum model. However, for systems which may admit valence bond ground states, such as the staggered J-J' Heisenberg antiferromagnet, single site mean field approximation is obviously an incorrect zeroth order approximation. In this paper, we introduce a mean field approximation for clusters consisting of two spins connected by a strong bond in the aforementioned model. We identify the quantum critical point and calculate the ground state magnetization within this cluster mean field approximation in one and two dimensions. Finally, we derive an effective dimer Hamiltonian, in the standard basis operator formalism, which may be a basis for further spin-wave like expansions around the cluster mean field approximation ground state.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 168-170
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Ground-State of the Quantum Spin-1/2 Heisenberg Antiferromagnet on Square-Kagomé Lattice: Resonating Valence Bond Description
    Autorzy:
    Tomczak, P.
    Molińska, A.
    Richter, J.
    Schulenburg, J
    Powiązania:
    https://bibliotekanauki.pl/articles/2046847.pdf
    Data publikacji:
    2006-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.45.+j
    75.50.Ee
    Opis:
    In this paper we report on some ground-state properties of the spin-1/2 Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. Finite N-spin systems were investigated with the use of the resonating valence bond method. Like in the case of spin system on kagomé lattice we find the almost flat dependence of mean singlet length on 1/N.
    Źródło:
    Acta Physica Polonica A; 2006, 109, 6; 781-787
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    New S=1/2 Alternating Chain Compound - High Pressure Form of (VO)$\text{}_{2}$P$\text{}_{2}$O$\text{}_{7^{-}}$
    Autorzy:
    Azuma, M.
    Saito, T.
    Hiroi, Z.
    Takano, M.
    Narumi, Y.
    Kindo, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2012882.pdf
    Data publikacji:
    2000-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.40.Cx
    75.50.Ee
    Opis:
    The high-pressure phase of (VO)$\text{}_{2}$P$\text{}_{2}$O$\text{}_{7}$ comprises a unique kind of spin-1/2 Heisenberg alternating antiferromagnetic chain, in contrast with the ambient pressure phase containing two crystallographically different chains. Magnetic susceptibility and high-field magnetization data showed the presence of a single spin gap of 23 (magnetization) ~27 (susceptibility) K, not double as observed for the ambient pressure phase. This result shows that the two kinds of chains of the ambient pressure phase have single, different spin gaps.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 1; 205-208
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Heisenberg Antiferromagnet on a 1/7-Depleted Triangular Lattice
    Autorzy:
    Schulenburg, J.
    Richter, J.
    Betts, D. D.
    Powiązania:
    https://bibliotekanauki.pl/articles/2013992.pdf
    Data publikacji:
    2000-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Hk
    75.10.Jm
    75.40.Mg
    75.50.Ee
    Opis:
    Based on the triangular lattice and its depletions there are three simple frustrated antiferromagnetic Heisenberg models in two dimensions. The first two, the triangular and kagomé lattices, have been examined in the recent past. The triangular lattice seems to have a long range order whereas the kagomé does not show the long range order. But these results are still controversial. This work is concentrated on a third type of this lattice family in order to improve the understanding of the connection between the long range order and coordination number in low dimensional systems. Bets has described the geometric properties of this lattice. It has a coordination number 5, which lies precisely between coordination numbers 6 and 4 of the other two lattices. The low-lying spectra and the correlation functions of finite lattices have been examined to discuss the possibility of a long range ordered ground state in the 1/7-depleted triangular lattice. The low-lying spectrum is generated by an exact diagonalization, and the tower of states behavior points to a long range ordered ground state.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 5; 971-974
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground-State Energy of Biquadratic Spin Systems (S=3/2) in the (1/z)$\text{}^{1}$-Approximation
    Autorzy:
    Błaszczak, E.
    Aksamit, J.
    Franek, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2035740.pdf
    Data publikacji:
    2003-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.30.Ds
    75.30.Et
    75.50.Ee
    Opis:
    Corrections to the molecular-field ground-state energies of the Heisenberg model with isotropic biquadratic interactions (spin S=3/2) are calculated in the (1/z)$\text{}^{1}$-approximation using the diagrammatic technique based on the Wick reduction theorem (z is the number of spins interacting with any given spin). The present results for the antiferri- and antiferromagnetic phases complete the previously obtained data for the antiquadrupolar, ferri- and ferromagnetic phases. From among the boundaries between different ground states only that between the antiferri- and antiferromagnetic phases is shifted with respect to its molecular-field value.
    Źródło:
    Acta Physica Polonica A; 2003, 103, 4; 403-414
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Response of Mn(III)F(salen) at Low Temperatures
    Autorzy:
    Park, J.
    Risset, O.
    Shiddiq, M.
    Peprah, M.
    Knowles, E.
    Andrus, M.
    Beedle, C.
    Ehlers, G.
    Podlesnyak, A.
    Čižmár, E.
    Nagler, S.
    Hill, S.
    Talham, D.
    Meisel, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1368508.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.50.Ee
    78.70.Nx
    76.30.-v
    75.10.Jm
    Opis:
    The low temperature magnetic response of Mn(III)F(salen), salen = $H_{14}C_{16}N_{2}O_{2}$, an S=2 linear-chain system, has been studied. Using a single crystal with the field applied perpendicular to the chain direction, torque magnetometry, down to 20 mK and up to 18 T, revealed a feature at 3.8 T when T ≤ 400 mK. ESR ( ≈200 GHz) studies, using single crystals at 4 K and in 5 T, have not detected any signal. In 10 mT, the temperature dependence of the susceptibility of powder-like samples can be reasonably fit when J/$k_{B}$=50 K and g=2. In addition, these data are unchanged for P ≤1.0 GPa. Using a randomly-oriented, powder-like, deuterated (12 of 14 H replaced by D) sample of 2.2 g at 270 mK, neutron scattering data, acquired with the Cold Neutron Chopper Spectrometer at the Spallation Neutron Source, show several well defined excitations that may be from the zero-field energy levels of antiferromagnetic S=2 spins with g=2, J/$k_{B}$=50 K, D/$k_{B}$=2.8 K, and E/$k_{B}$=0.5 K.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 228-229
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetization Process and Adiabatic Demagnetization of the Antiferromagnetic Spin-1/2 Heisenberg Cubic Cluster
    Autorzy:
    Strečka, J.
    Čisárová, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1366469.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.30.Sg
    75.40.Cx
    75.50.Ee
    75.60.Ej
    Opis:
    A full energy spectrum of the spin-1/2 Heisenberg cubic cluster is used to investigate a low-temperature magnetization process and adiabatic demagnetization of this zero-dimensional 2×2×2 quantum spin system. It is shown that the antiferromagnetic spin-1/2 Heisenberg cube exhibits at low enough temperatures a stepwise magnetization curve with four intermediate plateaux at zero, one quarter, one half, and three quarters of the saturation magnetization. We have also found the enhanced magnetocaloric effect close to level-crossing fields that determine transitions between the intermediate plateaux.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 26-27
    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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