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Wyświetlanie 1-15 z 100
Tytuł:
Thermodynamics of Ising Ferromagnet Studied by the Real-Space Renormalization Group Method
Autorzy:
Reich, W.
Piotrkowska, K.
Esposito, U.
Caramico D'Auria, A.
Powiązania:
https://bibliotekanauki.pl/articles/1929558.pdf
Data publikacji:
1993-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.Ak
75.40.Cx
Opis:
The critical exponents of the 3D Ising model were calculated in the approximation of the fourth-order cumulant expansion. Thermodynamic functions in the high-temperature range are obtained.
Źródło:
Acta Physica Polonica A; 1993, 84, 2; 275-278
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Direct Simulations of the Quantum Model for CsNiF$\text{}_{3}$
Autorzy:
Caramico D'Auria, A.
Esposito, F.
Esposito, U.
Kamieniarz, G.
Dekeyser, R.
Powiązania:
https://bibliotekanauki.pl/articles/1930597.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.Cn
75.10.Dg
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
We address the problem of reliability of a finite-chain technique for CsNiF$\text{}_{3}$. 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.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 409-412
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effective Field Methods for Magnetic Systems
Autorzy:
Kamieniarz, G.
Dekeyser, R.
Musiał, G.
Powiązania:
https://bibliotekanauki.pl/articles/1930600.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.Cn
64.60.Fr
05.50.+q
75.10.Dg
75.10.Hk
75.10.Jm
75.40.Cx
75.40.Mg
Opis:
The self-consistency conditions inherent in the mean-field approximation are extended to take into account some pair correlations. Ii is shown that this extension is systematically improvable and applicable to the spin systems with short-range interactions in the entire temperature region. With two correlations included and the renormalization-group ideas implemented, the critical properties of the Ising model are satisfactorily revealed. Moreover, the improved estimates of the thermodynamical quantities for the quantum linear XY model from the finite-size calculations are found down to very low temperatures.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 413-417
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Phonon Dispersion in Alkali Metals
Autorzy:
Gajjar, P. N.
Thakore, B. Y.
Patel, H. K.
Jani, A. R.
Powiązania:
https://bibliotekanauki.pl/articles/1933617.pdf
Data publikacji:
1995-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.25.Cx
63.20.Dj
Opis:
In the present paper, the calculation of the phonon dispersion relations for alkali metals to second order in a local pseudopotential is discussed in terms of the real-space sum. Different forms of dielectric functions are employed to judge the varying effects of exchange and correlation on the phonon frequencies. The quantitative agreement of phonon frequencies for the alkali metals reflects, satisfactorily, the experimental trend.
Źródło:
Acta Physica Polonica A; 1995, 88, 3; 489-502
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Anomalous Magnetic Properties of URuGa
Autorzy:
Tran, V. H.
Troć, R.
Powiązania:
https://bibliotekanauki.pl/articles/1964580.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.15.Qm
75.40.Cx
75.80.+q
Opis:
We present data of the magnetic susceptibility χ(T) and electrical resistivity ρ(T) for the hexagonal URuGa (space group P6̅2m). Below 7 K, χ increases rapidly and the data can be described by the expression χ(T) = χ(0)(1-a√T). ρ(T) in zero field follows the activated form: ρ(T)∼ exp(E$\text{}_{a}$/2k$\text{}_{B}$T ) with E$\text{}_{a}$ = 1.9 meV. In an applied magnetic field of 1 T, the resistivity varies as ρ(T)∼ bT. Between 18 and 250 K the resistivity is linear in -lnT and consistent with a Kondo-like effect.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 299-302
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Susceptibility of Sr$\text{}_{2}$CuO$\text{}_{3}$ and SrCu$\text{}_{2}$O$\text{}_{3}$
Autorzy:
Johnston, D. C.
Powiązania:
https://bibliotekanauki.pl/articles/1953177.pdf
Data publikacji:
1997-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.72.Jt
74.25.Ha
75.40.Cx
Opis:
The observed magnetic susceptibility χ$\text{}^{obs}$(T) data of Ami et al. for the linear-chain cuprate Sr$\text{}_{2}$CuO$\text{}_{3}$ are re-analyzed in terms of recent theory of Eggert et al. for the spin susceptibility χ(T) of the spin S=1/2 linear-chain Heisenberg antiferromagnet, which yielded the Cu-Cu exchange constant J/k$\text{}_{B}$=2150 K. Values for J', the exchange constant in the rungs, and J, that in the legs, were estimated for the S=1/2 two-leg ladder compound SrCu$\text{}_{2}$O$\text{}_{3}$, using the χ(T) data of Azuma et al. The analyses suggest that J'/J ≈ 0.5, contrary to the expectation that J'/J ≈ 1, and that J/k$\text{}_{B}$ is very large ( ≈ 2000 K), similar to that in Sr$\text{}_{2}$CuO$\text{}_{3}$.
Źródło:
Acta Physica Polonica A; 1997, 91, 1; 181-189
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chemical Potential Derivative as Hallmark for Phase Transitions
Autorzy:
Pietruszka, M.
Matlak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2011158.pdf
Data publikacji:
1999-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
75.40.Cx
75.50.Ee
Opis:
We study antiferromagnetic properties of the two-band extended s-f model with fluctuating valence in the context of two mutually bound new effects of chemical potential critical behaviour, as well as of critical electron redistribution. In order to exemplify both phenomena we build phase diagrams of the system displaying the dependence of the critical Néel temperatures (T$\text{}_{N}$) of the system versus 4f (5f) level positions. The phase diagram consists of two different areas corresponding to antiferromagnetic and paramagnetic phases. We plot the magnetizations and the correlation functions of the system as functions of temperature. Next, we investigate the temperature dependence of the relative average occupation numbers Δn$\text{}^{f(d)}$ and the chemical potential Δμ for a given 4f (5f) level position E$\text{}_{f}$. Plotting this quantities along the E$\text{}_{f}$ cross-section lines we observe small (of the order of 10$\text{}^{-4}$-10$\text{}^{-3}$) but well localized kinks exactly at the Néel temperature T$\text{}_{N}$. Last but not least, we plot the first derivative of the chemical potential dμ/dT which, as it shows clearly visible jumps at T$\text{}_{N}$, may turn out to be very accurate and sensitive (auxiliary) tool to find critical temperatures of the considered system. Moreover, we plot the difference μ$\text{}_{AF}$-μ$\text{}_{PARA}$ where we subtract a chemical potential value of a reference paramagnetic sample from the actual value of the antiferromagnetic system. Also in this case we report the observation of discontinuous change in slope at T$\text{}_{N}$. Our observations can be extended to point out to a new practical possibility of how to find experimentally the critical temperatures of the antiferromagnetic systems exclusively from the chemical potential measurements. We expect that the same type of measurement, according to our recent and present results, would also apply to all types of critical phenomena in real solids.
Źródło:
Acta Physica Polonica A; 1999, 96, 6; 725-732
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chemical Potential as a Detector of Phase Transitions in Solids
Autorzy:
Matlak, M.
Gosławska, E.
Grabiec, B.
Eid, Kh.
Powiązania:
https://bibliotekanauki.pl/articles/2012963.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.70.-b
75.30.Kz
75.40.Cx
Opis:
We show that the chemical potential exhibits small but distinct kinks at all critical temperatures as the evidence for phase transitions in the electronic system, structural phase transitions included. In the case of, at least, two kinds of interacting electrons average occupation numbers exhibit the same behavior.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 365-368
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chemical Potential Evidence for Phase Transitions in Magnetic and Superconducting Compounds and Alloys
Autorzy:
Matlak, M.
Pietruszka, M.
Powiązania:
https://bibliotekanauki.pl/articles/2012914.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.70.-b
75.30.Kz
75.40.Cx
Opis:
We announce that all phase transitions (induced by temperature or concentration) including structural ones and transitions between metastable or "exotic" states can be detected by the chemical potential critical behaviour, as well as, from the average occupation numbers of the electronic system (critical electron redistribution).
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 253-256
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental Studies of S=1 Heisenberg Planar Antiferromagnetic Chain Ni(C$\text{}_{11}$H$\text{}_{10}$N$\text{}_{2}$O)$\text{}_{2}$Ni(CN)$\text{}_{4}$
Autorzy:
Čizmár, E.
Černák, J.
Orendáč, M.
Herrmannsdörfer, T.
Feher, A.
Powiązania:
https://bibliotekanauki.pl/articles/2013230.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
71.20.Be
75.50.Ee
Opis:
In this paper we discuss the results of experimental studies of specific heat and magnetic susceptibility of chain compound Ni(C$\text{}_{11}$H$\text{}_{10}$N$\text{}_{2}$O)$\text{}_{2}$Ni(CN)$\text{}_{4}$. We have observed a Schottky type anomaly at T=2.2 K in a temperature dependence of specific heat and the compound was identified as a S=1 Heisenberg antiferromagnetic chain with the subcritical exchange coupling D/k$\text{}_{B}$=5 K, D/|J|=5.2 and the strong in-plane anisotropy E/k$\text{}_{B}$=2.8 K. It has been found that the in-plane anisotropy affects the region of validity of a diluted exciton model [1] and a strong coupling model [2] for S=1 Heisenberg chains with the strong planar anisotropy. The analysis suggests that the in-plane anisotropy should be considered in any attempt to find a compound potentially located in the boundary of Haldane and "large-D" phases.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 579-582
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
KEr(MoO$\text{}_{4}$)$\text{}_{2}$ and CsDy(MoO$\text{}_{4}$)$\text{}_{2}$ - Low-Dimensional Ising Magnets
Autorzy:
Kačmár, M.
Orendáčová, A.
Čizmár, E.
Horváth, D.
Orendáč, M.
Bondarenko, V.
Anders, A. G.
Feher, A.
Jaščur, M.
Powiązania:
https://bibliotekanauki.pl/articles/2013657.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.10.Hk
75.40.Mg
Opis:
In the present work the behaviour of cluster excitations in magnetic field, B, parallel to the easy axis was experimentally studied by the measurements of KEr(MoO$\text{}_{4}$)$\text{}_{2}$ and CsDy(MoO$\text{}_{4}$)$\text{}_{2}$ specific heat, C, vs. B dependence studied at a constant temperature. Corresponding Monte Carlo simulations of C revealed that despite of the fact that the Ising exchange-coupling models proved useful for a sufficient description of the specific heat of these dipolar systems in B=0, the analysis of current experimental data requires a partial renormalization of exchange-coupling constants previously obtained from B=0 analysis. The influence of crystal field effects and long-range character of spin correlations is discussed.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 807-810
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Characteristics of the System of Exchange Coupled Layers
Autorzy:
Urbaniak-Kucharczyk, A.
Machowski, S.
Powiązania:
https://bibliotekanauki.pl/articles/2013215.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.70.Ak
75.30.-m
75.40.Cx
Opis:
Using the Green function method it is shown that the deviation of the Curie temperature from its value calculated for continuous layers is related to the absolute value of the interlayer coupling parameter. The dependence of spin wave stiffness parameter on the interlayer exchange coupling is also found.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 543-546
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Properties of Spin-Ladders (A$\text{}_{2}$Cu$\text{}_{2}$O$\text{}_{3}$)$\text{}_{m}$ (CuO$\text{}_{2}$)$\text{}_{n}$
Autorzy:
Baran, M.
Szymczak, H.
Szymczak, R.
Dyeyev, S.
Leonyuk, L.
Babonas, G.-J.
Powiązania:
https://bibliotekanauki.pl/articles/2013220.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.40.Cx
75.30.Gw
75.45.+j
75.90.+w
Opis:
Magnetization M(T) and M(H) data of single crystals of the S=1/2 quasi-one-dimensional system (A$\text{}_{2}$Cu$\text{}_{2}$O$\text{}_{3}$)$\text{}_{m}$(CuO$\text{}_{2}$)$\text{}_{n}$ with various A-site constituents are compared. The studied orthorhombic, incommensurate crystals are characterized by m/n=5/7,7/10, and 9/13. The role of rare-earth ions located in A-sites is discussed.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 571-574
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Manifestation of Spin-Glass-Like Behavior in the Organometallic Magnet
Autorzy:
Dyakonov, V. P.
Arciszewska, M.
Dobrowolski, W.
Szewczyk, A.
Szymczak, H.
Aksymentieva, E.
Varyukhin, V.
Zubov, E.
Gutowska, M. U.
Powiązania:
https://bibliotekanauki.pl/articles/2013705.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Kz
75.40.Cx
Opis:
Ac susceptibility (χ$\text{}_{ac}$) and dc magnetization (M$\text{}_{dc}$) of the organometallic magnet Na[FeO$\text{}_{6}$(C$\text{}_{10}$H$\text{}_{8}$N)$\text{}_{3}$] have been studied in temperature range of 4.2-200 K, in an external magnetic field up to 16 kOe. Some peculiarities of the χ$\text{}_{ac}$ and M $\text{}_{dc}$ behavior, which are characteristic of spin-glasses, e.g. cusps in the susceptibility and zero-field-cooled magnetization, an irreversibility between the field-cooled and zero-field-cooled magnetization and dependences of the T$\text{}_{cusp}$ temperature on the frequency and the intensity of the magnetic field, were observed at low temperatures.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 863-866
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
Wyświetlanie 1-15 z 100

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