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    Wyświetlanie 1-28 z 28
    Tytuł:
    Spin-1/2 XXZ Diamond Chain within the Jordan-Wigner Fermionization Approach
    Autorzy:
    Verkholyak, T.
    Strečka, J.
    Jaščur, M.
    Richter, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1535012.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.10.Pq
    Opis:
    The spin-1/2 XXZ diamond chain is considered within the Jordan-Wigner fermionization. The fermionized Hamiltonian contains the interacting terms which are treated within the Hartree-Fock approximation. We obtain the ground-state magnetization curve of the model for some particular cases and compare the results with the exact diagonalization data for finite chains of 30 spins and known exact results. We also analyze the validity of the suggested approximation.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 978-979
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Exchange Interactions and Estimation of $T_N$ in $CsNiF_3$ from First Principles
    Autorzy:
    Legut, D.
    Rusz, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813855.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    75.30.Et
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 503-506
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermodynamics of the Exactly Solvable Spin-Electron Tetrahedral Chain
    Autorzy:
    Gálisová, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402558.pdf
    Data publikacji:
    2015-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    05.70.-a
    75.10.Pq
    Opis:
    An exactly solvable spin-electron tetrahedral chain, where the Ising spins localized at nodal lattice sites regularly alternate with three equivalent lattice sites available for one mobile electron is considered. The system with ferromagnetic interaction between the Ising spins and electrons exhibits an enhanced magnetocaloric effect in the limit H/|J| → 0 when the entropy is very small, whereas the system with antiferromagnetic interaction between the Ising spins and electrons exhibits an enhanced magnetocaloric effect around the field H/J=1 when the entropy is sufficiently close to the value S/2N = ln[(1+√5)/2]. We study the thermodynamics of the system in these field regions.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 2; 156-158
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    On Theoretical Study of Magnetic Behavior of Diamond Doped with Transition Metals
    Autorzy:
    Hussain, F.
    Ullah, M.
    Ullah, H.
    Rashid, M.
    Imran, M.
    Ahmad, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399279.pdf
    Data publikacji:
    2015-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Kt
    75.10.Pq
    75.30.Hx
    Opis:
    We study the magnetic behavior of the diamond system. In this system diamond bulk is involved which is doped with different transition metals, namely Cu, Cd, Hg, and Zn. The VASP code is employed for all calculations which are based on density functional theory. The substitutional point defects is introduced in the diamond bulk and occupied by the transition metals. Results exhibit that all transition metals show ferromagnetism behavior and Cu is a good advocate of conductivity among all transition metals. The range of magnetic moments is 2.89, 1.99, 1.96, and 1.80 $μ_{B}$ per Cu, Cd, Hg, and Zn atom in diamond bulk, respectively. Strong magnetic behavior points out that these materials could be used for spintronics.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 3; 823-826
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spin Chain in Magnetic Field: Limitations of the Large-N Mean-Field Theory
    Autorzy:
    Wohlfeld, K.
    Chen, Cheng-Chien
    van Veenendaal, M.
    Devereaux, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/1384813.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    75.10.Jm
    75.10.Pq
    Opis:
    Motivated by the recent success in describing the spin and orbital spectrum of a spin-orbital chain using a large-N mean-field approximation, we apply the same formalism to the case of a spin chain in the external magnetic field. It occurs that in this case, which corresponds to N=2 in the approximation, the large-N mean-field theory cannot qualitatively reproduce the spin excitation spectra at high magnetic fields, which polarize more than 50% of the spins in the magnetic ground state. This, rather counterintuitively, shows that the physics of a spin chain can under some circumstances be regarded as more complex than the physics of a spin-orbital chain.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 201-203
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    $Cu_3(tmen)_3(tma)_2(H_2O)_2$ · $6.5H_2O$ - New S = 1/2 "Sawtooth" Chain?
    Autorzy:
    Vrábel, P.
    Orendáčová, A.
    Černák, J.
    Orendáč, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1535093.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.10.Pq
    75.30.Et
    Opis:
    The results of the investigation of magnetic susceptibility, magnetization and specific heat of $Cu_3(tmen)_3(tma)_2(H_2O)_2$ · $6.5H_2O$ (tmen = N,N,N',N'-tetramethylethane-1,2 diamine; $H_3$ tma = 1,3,5-benzenetricarboxylic acid) are reported. The spatial arrangement of magnetic Cu(II) ions and network of covalent bonds suggest that the studied material might be a representative of S = 1/2 sawtooth chain with moderate exchange coupling J/$k_{B}$. The investigation of the temperature dependence of susceptibility and magnetic field dependence of magnetization yielding J/$k_{B}$ ≈ - 0.63 K is consistent with the structural features. In addition, specific heat data reveal short-range correlations in milikelvin temperature range and indicate long-range ordering below 150 mK.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 993-994
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Kinetically-Driven Frustration in Hybrid Spin Ladders
    Autorzy:
    Carvalho, R.
    Pereira, M.
    Lyra, M.
    Rojas, O.
    Strecka, J
    Powiązania:
    https://bibliotekanauki.pl/articles/1199484.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.10.Pq
    05.70.Ce
    Opis:
    We introduce a spin ladder model incorporating localized and delocalized spins, which is exactly solvable using the decoration-iteration and transfer-matrix techniques. Quantum correlations between delocalized spins induce an antiferromagnetic coupling between the spin chains that competes with a direct ferromagnetic exchange coupling. A resulting kinetically-driven frustration is predominant in the regime of low temperatures and large hopping amplitudes. We provide the full ground-state phase diagram, as well as the frustration diagram on distinct coupling regimes.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 12-13
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Polaron States in a CuO Chain
    Autorzy:
    Bieniasz, K.
    Oleś, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1385209.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    72.10.Di
    75.10.Pq
    75.50.Ee
    Opis:
    We introduce a one-dimensional model for a CuO chain, with holes and S=1/2 spins localized in $3d_{x²-y²}$ orbitals, and p_σ oxygen orbitals without holes in the ground state. We consider a single hole doped at an oxygen site and study its propagation by spin-flip processes. We develop the Green function method and treat the hole-spin coupling in the self-consistent Born approximation, similar to that successfully used to study polarons in the regular t-J model. We present an analytical solution of the problem and investigate whether the numerical integration is a good approximation to this solution.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 269-271
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Comparison of the Multi-Band Hubbard and Heisenberg Models on Small Finite Clusters
    Autorzy:
    Matysiak, J.
    Lemański, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1030762.pdf
    Data publikacji:
    2018-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    31.15.vq
    75.10.Jm
    75.10.Pq
    Opis:
    We perform exact numeric calculations for a few versions of the two-orbital Hubbard model on the four site cluster. We show that the conventional spin 1 Heisenberg Hamiltonian can be obtained in the strong coupling limit, but only for some versions of the two-orbital Hubbard model. Then we propose a modified version of the Heisenberg Hamiltonian, that we call the two-orbital Heisenberg model, which is relevant in those cases, where the conventional spin 1 Heisenberg model fails.
    Źródło:
    Acta Physica Polonica A; 2018, 133, 3; 405-407
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetocaloric Effect in NiCl₂(bipy) at Low Temperatures
    Autorzy:
    Ráczová, K.
    Čižmár, E.
    Feher, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032298.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.30.Sg
    75.30.Gw
    75.10.Pq
    Opis:
    Magnetothermal properties of the compound NiCl₂(bipy), where bipy = 4,4'-bipyridine, were studied. The single-ion anisotropy of Ni(II) ions was estimated and its influence on magnetocaloric effect in NiCl₂(bipy) was investigated. Above the metamagnetic transition a maximum in the isothermal change of the magnetic entropy is reached near 11 K at field change from 0T to 7T with peak value -ΔS = 6J K¯¹ kg¯¹. The temperature dependence of ΔS above 7K agrees with the assumed easy-axis type of single-ion anisotropy. The inverse magnetocaloric effect, typical for ordered antiferromagnets, was observed in the ordered state of NiCl₂(bipy) only for isothermal magnetization in small fields up to 2T.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 922-924
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The magnetocaloric effect in {[Cu(bapa)]₃[Cr(CN)₆]₂}ₙ · 6n H₂O at low temperatures
    Autorzy:
    Ráczová, K.
    Vavra, M.
    Hegedüs, M.
    Čižmár, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1048121.pdf
    Data publikacji:
    2018-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.30.Sg
    75.30.Gw
    75.10.Pq
    Opis:
    The crystals of {[Cu(bapa)]₃[Cr(CN)₆]₂}ₙ·6nH₂O (bapa = bis(3-aminopropyl)amine) are formed by infinite Cu(II)-Cr(III) antiparallel chains, which are connected into the third direction by additive [Cu(bapa)] moieties. The onset of long-range magnetic order at 3.2 K was observed by AC susceptibility. The study of the magnetocaloric effect from magnetization measurements yields a large entropy change -ΔS_{M} = 13.65 J K¯¹mol¯¹ (-ΔS_{M} = 12.25 J kg¯¹K¯¹) at the field change from 0 T to 3 T at temperature 4 K. The analysis of the critical behavior of -ΔS_{M} suggests the value of critical exponent n = 0.577 at the ordering temperature characteristic for three-dimensional magnets with Ising anisotropy.
    Źródło:
    Acta Physica Polonica A; 2018, 133, 3; 429-431
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermal Entanglement and Quantum Non-Locality along the Stepwise Magnetization Curve of the Spin-1/2 Ising-Heisenberg Trimerized Chain
    Autorzy:
    Strečka, J.
    Pavličko, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032512.pdf
    Data publikacji:
    2017-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    75.10.Jm
    75.40.Cx
    75.60.Ej
    Opis:
    The spin-1/2 Ising-Heisenberg trimerized chain in a magnetic field is revisited with the aim to explore the quantum entanglement and non-locality within the exactly solved spin system, which exhibits in a low-temperature magnetization curve two intermediate plateaux at zero and one-third of the saturation magnetization. The ground-state phase diagram involves two quantum (antiferromagnetic, ferrimagnetic I) and two classical (ferrimagnetic II, saturated paramagnetic) phases. We have rigorously calculated the concurrence and Bell function in order to quantify the quantum entanglement and non-locality at zero as well as non-zero temperatures. It is demonstrated that the entanglement can be thermally induced also above the classical ground states unlike the quantum non-locality, which means that the thermal entanglement is indispensable for a violation of the locality principle.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 1; 167-169
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Frustration-Driven Quantum Phase Transition in the 1D Extended Anisotropic Heisenberg Model
    Autorzy:
    Plekhanov, E.
    Avella, A.
    Mancini, F.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813777.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.30.Kz
    75.10.Pq
    75.40.Mg
    Opis:
    By using density matrix renormalization group technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions induced by frustration. By increasing the next-nearest-neighbor interaction, the ground state of the system changes smoothly from a completely polarized state to a next-nearest-neighbor correlated one. On the contrary, letting the in-plane interaction to be greater than the out-of-plane one, the ground state changes abruptly.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 429-432
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Low-Temperature Thermodynamics of Spin-1/2 Orthogonal-Dimer Chain with Ising and Heisenberg Interactions
    Autorzy:
    Verkholyak, T.
    Strečka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1199501.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Jm
    75.10.Pq
    75.30.Gw
    75.40.Cx
    Opis:
    We consider an exactly solvable version of the quantum spin-1/2 orthogonal-dimer chain with the Heisenberg intra-dimer and Ising inter-dimer couplings. The investigated quantum spin system exhibits at zero temperature fractional plateaux at 1/4 and 1/2 of the saturation magnetization and it has a highly degenerate ground state at critical fields where the magnetization jumps. We study the field dependence of the specific heat at low temperature. The lattice-gas description is formulated in a vicinity of critical fields to explain the low-temperature behaviour of specific heat.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 22-23
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Anisotropy, Geometric Structure and Frustration Effects in Molecule-Based Nanomagnets
    Autorzy:
    Kamieniarz, G.
    Kozłowski, P.
    Antkowiak, M.
    Sobczak, P.
    Ślusarski, T.
    Tomecka, D.
    Barasiński, A.
    Brzostowski, B.
    Drzewiński, A.
    Bieńko, A.
    Mroziński, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1426672.pdf
    Data publikacji:
    2012-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.50.Xx
    75.10.Jm
    75.10.Pq
    75.40.Cx
    Opis:
    In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n → ∞) frustration can be considered as the opposite to bipartiteness in the odd numbered (3 ≤ n ≤ 9) s = 3/2 quantum spin rings. We analyse the influence of exchange interactions and anisotropy on magnetic susceptibility of bimetallic (S = 3/2, s = 1/2) chains composed of Cu ions linked to different 3d ions by fitting experimental data. We reach the remarkable consistency of the density functional theory estimates of the magnetic couplings in $Cr_8$ molecule and provide strong support to the spin models exploited in the literature.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 5-6; 992-998
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Some Exact Results in the One-Dimensional Attractive Hubbard Model
    Autorzy:
    Jakubczyk, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402562.pdf
    Data publikacji:
    2015-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    03.65.Aa
    03.65.Fd
    Opis:
    The one-dimensional attractive Hubbard model (Ułl 0) is discussed for the chains of N nodes and the same number of electrons, where N-1 of them have the same spin projection, assuming periodic boundary conditions and the half-filling case. Based on the analysis of the eigenvalue problem we provided the general analytical expression for the eigenvalues, for any number N. This formula implies the existence of two elementary particles with mutually dependent momenta on the ring with N sites the same number of electrons including N-1 of the same spin projection.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 2; 170-172
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    On the Exact Solution of the Mixed-Spin Ising Chain with Axial and Rhombic Zero-Field Splitting Parameters
    Autorzy:
    Dančo, M.
    Strečka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1506905.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    05.50.+q
    05.70.Jk
    75.10.Pq
    Opis:
    Ground-state phase diagram of the mixed spin-1/2 and spin-1 Ising chain with axial and rhombic zero-field splitting parameters is exactly calculated within the framework of the transfer-matrix method. It is shown that the rhombic zero-field splitting parameter prefers the magnetically ordered phase instead of the disordered phase.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 728-729
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Quantum versus Classical Polarons in a Ferromagnetic $CuO_3$-Like Chain
    Autorzy:
    Bieniasz, K.
    Oleś, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1374771.pdf
    Data publikacji:
    2014-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    72.10.Di
    75.10.Pq
    75.50.Dd
    79.60.-i
    Opis:
    We present an exact solution for an itinerant hole added into the oxygen orbitals of a $CuO_{3}$-like ferromagnetic chain. Using the Green function method, the quantum polarons obtained for the Heisenberg SU(2) interaction between localized Cu spins are compared with the polarons in the Ising chain. We find that magnons with large energy are favorable towards quasiparticle existence, even in the case of relatively modest electron-magnon coupling. We observe two quasiparticle states with dispersion ~2t each, which emerge from the incoherent continuum when the exchange coupling J increases. Quantum fluctuations in the spin system modify the incoherent part of the spectrum and change the spectral function qualitatively, beyond the bands derived from the perturbation theory.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 4a; A-80-A-83
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Approximate Approach to Magnetic and Thermodynamic Properties of Mixed Spin (1/2-S) Chains with AB and $AB_2$ Topology
    Autorzy:
    Pełka, R.
    Pinkowicz, D.
    Powiązania:
    https://bibliotekanauki.pl/articles/1534880.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    71.70.Gm
    75.30.Cr
    75.40.Cx
    Opis:
    Motivated by the rapid development in the synthesis of novel molecule-based magnets, we have investigated magnetic and thermodynamic properties of mixed spin (s-S) exchange coupled chains displaying a simple linear AB or a knotted $AB_2$ arrangement. Approximate approach for s = 1/2 and S ≥ 5/2, treating at an intermediate step spin S operator as a commuting variable and using the transfer matrix technique, is used. Susceptibility, magnetization and heat capacity of both spin systems are evaluated numerically from the corresponding free energy for S = 5/2. Uniform ferromagnetic and antiferromagnetic couplings are discussed. The procedure reproduces the right values of saturation magnetization and the entropy content of the systems, corroborating its correctness. χ T curves are shown to depend crucially on the $μ_{B}$ H/J ratio. For zero-field heat capacity a double-peak structure is revealed for the AB chain, whereas for the $AB_2$ chain only one broad anomaly is observed.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 959-961
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A Coupled Spin-Electron Diamond Chain with Different Landé g-Factors of Localized Ising Spins and Mobile Electrons
    Autorzy:
    Torrico, J.
    Pereira, M.
    Strečka, J.
    Lyra, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032419.pdf
    Data publikacji:
    2017-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    05.50.+q
    75.10.Pq
    75.30.Kz
    75.40.Cx
    Opis:
    A coupled spin-electron diamond chain with localized Ising spins placed on its nodal sites and mobile electrons delocalized over interstitial sites is explored in a magnetic field taking into account the difference between the Landé g-factors of the localized spins and mobile electrons. The ground-state phase diagram is constituted by two classical ferrimagnetic phases, the quantum unsaturated paramagnetic phase and the saturated paramagnetic phase. Both classical ferrimagnetic phases as well as the unsaturated paramagnetic phase are reflected in a low-temperature magnetization curve as intermediate magnetization plateaus. The unsaturated paramagnetic phase is quantum in its character as evidenced by the fermionic concurrence calculated for a pair of the mobile electrons hopping in between the interstitial sites. It is shown that the magnetic field can under certain conditions induce a quantum entanglement above the disentangled ground state.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 1; 140-142
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground State, Magnetization Process, and Magnetocaloric Effect of the Exactly Tractable Spin-Electron Tetrahedral Chain
    Autorzy:
    Gálisová, L.
    Strečka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1384829.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    75.60.Ej
    75.30.Sg
    05.50.+q
    Opis:
    A hybrid spin-electron system on one-dimensional tetrahedral chain, in which the localized Ising spin regularly alternates with the mobile electron delocalized over three lattice sites, is exactly investigated using the generalized decoration-iteration transformation. The system exhibits either the ferromagnetic or antiferromagnetic ground state depending on whether the ferromagnetic or antiferromagnetic interaction between the Ising spins and mobile electrons is considered. The enhanced magnetocaloric effect during the adiabatic demagnetization suggests a potential use of the investigated system for low-temperature magnetic refrigeration.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 216-218
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of the Canting of Local Anisotropy Axes on Ground-State Properties of a Ferrimagnetic Chain with Regularly Alternating Ising and Heisenberg Spins
    Autorzy:
    Torrico, J.
    Lyra, M.
    Rojas, O.
    de Souza, S.
    Strečka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032717.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    75.10.Kt
    75.30.Kz
    75.40.Cx
    75.60.Ej
    Opis:
    The effect of the canting of local anisotropy axes on the ground-state phase diagram and magnetization of a ferrimagnetic chain with regularly alternating Ising and Heisenberg spins is exactly examined in an arbitrarily oriented magnetic field. It is shown that individual contributions of the Ising and Heisenberg spins to the total magnetization basically depend on the spatial orientation of the magnetic field and the canting angle between two different local anisotropy axes of the Ising spins.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 621-623
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Breakdown of a Magnetization Plateau in Ferrimagnetic Mixed Spin-(1/2,S) Heisenberg Chains due to a Quantum Phase Transition towards the Luttinger Spin Liquid
    Autorzy:
    Strečka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1032725.pdf
    Data publikacji:
    2017-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Pq
    75.10.Kt
    75.30.Kz
    75.40.Cx
    75.60.Ej
    Opis:
    Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are calculated with the help of density-matrix renormalization group method for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown that the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective of the spin value S exactly one intermediate magnetization plateau, which can be identified with the gapped Lieb-Mattis ferrimagnetic ground state. The magnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at a quantum phase transition towards the Luttinger spin liquid, which is characterized by a continuous change of the magnetization with the magnetic field until another quantum critical point is reached at the saturation field.
    Źródło:
    Acta Physica Polonica A; 2017, 131, 4; 624-626
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Hilbert Space and the Exact Solution of the Spin-Electron Double-Tetrahedral Chain
    Autorzy:
    Jakubczyk, D.
    Gálisová, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402563.pdf
    Data publikacji:
    2015-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    02.20.-a
    05.30.-d
    75.10.Pq
    05.50.+q
    Opis:
    We discuss an exactly solvable double-tetrahedral chain, in which the localized Ising spins regularly alternate with triangular clusters - each available for one mobile electron. We give an exact solution for the considered hybrid system by the construction of the N-th tensor power of the Fourier transformation and using the generalized decoration-iteration mapping tranformation.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 2; 173-175
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground-State Properties of the Spin-1/2 Heisenberg-Ising Bond Alternating Chain with Dzyaloshinskii-Moriya Interaction
    Autorzy:
    Strečka, J.
    Gálisová, L.
    Derzhko, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/1506983.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    05.50.+q
    05.70.Jk
    64.60.De
    75.10.Pq
    Opis:
    Ground-state energy is exactly calculated for the spin-1/2 Heisenberg-Ising bond alternating chain with the Dzyaloshinskii-Moriya interaction. Under certain condition, which relates a strength of the Ising, Heisenberg and Dzyaloshinskii-Moriya interactions, the ground-state energy exhibits an interesting nonanalytic behavior accompanied with a gapless excitation spectrum.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 742-744
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A Lattice Dynamical Investigation of the Raman and the Infrared Wave Numbers of $MnWO_4$
    Autorzy:
    Gupta, H.
    Ruby, -
    Sinha, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1419784.pdf
    Data publikacji:
    2012-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.50.Ah
    63.22.Dc
    63.70.+h
    75.10.Pq
    78.30.-j
    Opis:
    A short-range force constant model has been applied using normal coordinate analysis to investigate the Raman and the infrared modes in multiferroic $MnWO_4$ having space group P2/c. The calculation of zone centre phonons has been made with eight stretching and seven bending force constants. The calculated Raman and infrared wave numbers are in good agreement with the observed ones. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wave numbers.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 1; 142-145
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mechanical Properties of Tetragonal and Orthorhombic Phases of Quasi-One-Dimensional Antiferromagnet $KCuF_{3}$
    Autorzy:
    Legut, D.
    Wdowik, U.
    Powiązania:
    https://bibliotekanauki.pl/articles/1366449.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    62.20.fk
    73.61.Ng
    62.20.de
    62.20.dj
    75.10.Pq
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 14-15
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Properties of an S=2 Ladder Spin Model Applied to a New Quasi-One-Dimensional Magnet $[Mn(phen)_{3}](TCNQ)_{2}·H_{2}O$
    Autorzy:
    Botko, M.
    Cheranovskii, V.
    Vasilets, G.
    Čižmar, E.
    Kajňaková, M.
    Anders, A.
    Starodub, V.
    Feher, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1366461.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.50.Xx
    75.10.Jm
    76.10.Pq
    Opis:
    The effective spin S=2 Heisenberg ladder model with free-spin admixtures was proposed for the study of the low-temperature magnetic properties of the complex compound $[Mn(phen)_{3}](TCNQ)_{2}·H_{2}O$. The temperature dependence of magnetic susceptibility was found to be close to experimental data.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 20-21
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-28 z 28

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