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Wyświetlanie 1-15 z 54
Tytuł:
One-Dimensional Falicov-Kimball Model in the Strong Coupling Limit
Autorzy:
Farkašovský, P.
Bat'ko, I.
Powiązania:
https://bibliotekanauki.pl/articles/1930516.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
Opis:
We studied the ground state properties of the one-dimensional Falicov-Kimball model in the strong coupling limit for special periodic and aperiodic configurations of ions. The ground state phase diagrams of the model for nearest neighbor and next nearest neighbor hopping are discussed.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 307-310
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Properties of R$\text{}_{1-x}^{(1)}$R$\text{}^{(2)}$$\text{}_{x}$Al$\text{}_{2}$ Alloys
Autorzy:
Matlak, M.
Ślebarski, A.
Powiązania:
https://bibliotekanauki.pl/articles/1887609.pdf
Data publikacji:
1991-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
Opis:
Using the multiband s-f model we derive the formulae determining the Curie temperature and magnetic moment as functions of concentration x for R$\text{}_{1-x}^{(1)}$R$\text{}_{x}^{(2)}$Al$\text{}_{2}$ intermetallic alloys, where R$\text{}^{1,2}$ denote magnetic rare earth metals. These formulae, applied to R$\text{}_{1-x}^{(1)}$R$\text{}^{(2)}$ alloys (R$\text{}^{(1)}$ = La, Lu, Y, Zr and R$\text{}^{(2)}$ = Gd) give the linear dependence of the Curie temperature and magnetic moment versus x in full agreement with experimental data.
Źródło:
Acta Physica Polonica A; 1991, 79, 5; 721-725
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Frustrated Magnetism in Vanadium Oxides
Autorzy:
Thalmeier, P.
Schmidt, B.
Yushankhai, V.
Takimoto, T.
Powiązania:
https://bibliotekanauki.pl/articles/1810285.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.10.Lp
Opis:
The effect of frustration in various localized and itinerant vanadium oxide compounds is discussed within next nearest neighbors Heisenberg and spin fluctuation models, respectively. In the localized moment case the S=1/2 $J_1-J_2$-model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signatures in the high field magnetization and in magnetocaloric quantities are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides of the type $AA'VO(PO_4)_2$ where A, A' = Pb, Zn, Sr, Ba, Cd. In itinerant electron systems magnetic frustration may emerge as a result of electron correlations on a geometrically frustrated lattice. This mechanism causes enhanced spin fluctuations in a large region of momentum space and therefore can lead to a heavy fermion state at low temperatures as in the 3d spinel compound $LiV_2O_4$. The evidence from neutron scattering and NMR experiments is discussed within self-consistent renormalization theory based on local density approximation band structure calculations.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 53-58
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Hofstadter Diagram Analyzed in Terms of the Band Structure Parameters for a Planar Metal
Autorzy:
Roliński, T.
Olszewski, S.
Powiązania:
https://bibliotekanauki.pl/articles/2046841.pdf
Data publikacji:
2006-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
75.70.-i
Opis:
It is demonstrated that a wing of the Hofstadter diagram calculated for the tightly-bound s-electrons in the simple cubic lattice can be reproduced by the dispersion figure of the wave-vector square considered for the electron states of the same lattice, on the condition that the states having equal energies are taken into account. The dispersion splitting increases systematically with the distance of the states from the Brillouin zone center. A similar wing due to dispersion of the electron momentum is calculated also for the s-electron states in the body-centered cubic lattice.
Źródło:
Acta Physica Polonica A; 2006, 109, 6; 753-759
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Pressure Effect on Magnetic Properties of UGa$\text{}_{3}$
Autorzy:
Grechnev, G. E.
Delin, A.
Eriksson, O.
Johansson, B.
Panfilov, A. S.
Svechkarev, I. V.
Kaczorowski, D.
Powiązania:
https://bibliotekanauki.pl/articles/1964627.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
75.20.En
Opis:
The magnetic susceptibility, χ, of the itinerant antiferromagnetic compound UGa$\text{}_{3}$ was studied under pressure up to 2 kbar in the temperature range 64-300 K. The measured pressure derivative of the Néel temperature is found to be dT$\text{}_{N}$/dP=-1.1 K/kbar. In order to analyze the experimental magnetovolume effect values, d lnχ/d lnV, the volume dependent electronic structure of UGa$\text{}_{3}$ has been calculated ab initio in a paramagnetic phase by employing a relativistic full-potential linear muffin tin orbital method and including an external magnetic field self-consistently. The calculations revealed a predominance of itinerant uranium f-states at the Fermi energy, as well as a large orbital contribution to χ.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 331-333
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Anomalous Diamagnetism of $YbPb_3$ Compound: Pressure Effects
Autorzy:
Baranovskiy, A.
Grechnev, G.
Panfilov, A.
Svechkarev, I.
Żogał, O.
Czopnik, A.
Hackemer, A.
Powiązania:
https://bibliotekanauki.pl/articles/1813626.pdf
Data publikacji:
2008-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
75.80.+q
Opis:
The effect of a uniform pressure on the magnetic susceptibility was measured for $YbPb_3$ compound, wherein a degeneracy point of the energy bands is located just below the Fermi level and responsible for the anomalous diamagnetism. Theoretical analysis of the experimental data has revealed that a pronounced increase of diamagnetism with pressure is governed by closing the degeneracy point towards the Fermi energy
Źródło:
Acta Physica Polonica A; 2008, 113, 1; 243-246
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theory of Strongly Correlated Systems in the Limit of Large On-Site Coulomb Repulsion
Autorzy:
Izyumov, Yu. A.
Powiązania:
https://bibliotekanauki.pl/articles/1860989.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
75.30.Cr
Opis:
A strongly correlated electronic system is studied within the framework of the t-J model with the help of diagram technique for the Hubbard X-operators. The summing of some series of diagrams is suggested, corresponding to the following three types of approximations: the generalized random phase approximation, the mean field approximation, and the low density approximation. In generalized random phase approximation the dynamic magnetic susceptibility of paramagnetic phase is calculated, and boundaries of stability of this phase are found on the plane of Hamiltonian parameters and electron concentration n. It is shown that at some critical concentration n$\text{}_{c}$ the system undergoes a crossover from the itinerant magnetism (n < $\text{}n_{c}$) to the magnetism with localized magnetic moments (n > $\text{}n_{c}$). Simultaneously, the system transfers from the Fermi-liquid behaviour to the regime of strong electron correlations with nonquasiparticle states. In mean field approximation equations for the order parameters were derived and phase transitions temperatures in a ferromagnetic and antiferromagnetic phases were obtained. In low density approximation a state of the saturated ferromagnetism was investigated and a critical concentration n$\text{}_{s}$ was calculated when the nonsaturated ferromagnetism follows the saturated ferromagnetism.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 103-115
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical and Mössbauer Effect Study of Magnetic and Electronic Properties of Fe$\text{}_{3}$Al Compound
Autorzy:
Deniszczyk, J.
Frąckowiak, J. E.
Powiązania:
https://bibliotekanauki.pl/articles/1956205.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Bb
75.10.Lp
Opis:
The electronic properties of Fe$\text{}_{3}$Al were determined experimentally, with the use of the Mossbauer spectroscopy, and theoretically. The band structure of the compounds was investigated applying the self-consistent tight-binding linear muffin tin orbital method. The calculated Fermi contact term of hyperfine fields and the isomer shifts are in good agreement with the values resulting from analysis of experimental data. The different kinds of electron transfer estimated on the base of the proposed "additive model" are also strongly supported by calculations.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 455-458
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Exchange Coupling in GdM Compounds
Autorzy:
Buschow, K. H.J.
Grechnev, G. E.
Hjelm, A.
Kasamatsu, Y.
Panfilov, A. S.
Svechkarev, I. V.
Powiązania:
https://bibliotekanauki.pl/articles/1964560.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.20.En
75.10.Lp
Opis:
The magnetic susceptibility of ferromagnetic GdM alloys (M=Cu$\text{}_{1-x}$Ga$\text{}_{x}$, Mg, Zn) has been investigated under helium gas pressure for temperatures above T$\text{}_{C}$. The evaluated pressure derivatives of the paramagnetic Curie temperature, dlnΘ/dP, appeared to be remarkably different for isovalent GdMg and GdZn compounds (-11.2 and -0.1 Mbar$\text{}^{-1}$, respectively). An analysis of the obtained dlnΘ/dP values for GdCu$\text{}_{1-x}$Ga$\text{}_{x}$ alloys and results of ab initio electronic structure calculations have revealed the essential role of 5d electrons as the mediators of exchange coupling in ferromagnetic GdM compounds. The pressure derivatives of T$\text{}_{C}$ were calculated by employing the modern mean-field theory, as well as the spin-fluctuation model. As a result, good agreement is found with the experimental values of dlnΘ/dP.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 267-270
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Phase Separation in Hubbard Model
Autorzy:
Samson, J. H.
Powiązania:
https://bibliotekanauki.pl/articles/1964683.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.25.+z
75.10.Lp
Opis:
The Hartree-Fock ground-state phase diagram of the one-dimensional Hubbard model is calculated in the μ-U plane, restricted to phases with no charge density modulation. This allows antiferromagnetism, saturated ferromagnetism, spiral spin density waves and a collinear structure with unit cell ↑↑↓↓. The spiral phase is unstable against phase separation near quarter-, half- and three-quarter-filling. For large U this occurs at hole (or electron) doping of (3t/π$\text{}^{2}$U)$\text{}^{1}\text{}^{/}\text{}^{3}$ from half-filling.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 363-366
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ferromagnetism in Hubbard Chains
Autorzy:
Cuoco, M.
Noce, C.
Romano, A.
Powiązania:
https://bibliotekanauki.pl/articles/1955828.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Lp
Opis:
We analyze the possible occurrence of ferromagnetism in the Hubbard model, by means of an exact diagonalization study performed on 3- to 8-site chains with periodic boundary conditions. In the case of one hole in the half-filled configuration, we find that the Nagaoka state is reached only in the 3- and in the 4-site case. Ground states characterized by unsaturated ferromagnetism are found when the case of more than one hole is considered.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 387-390
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ferromagnetic Systems with Hopping Interaction
Autorzy:
Górski, G.
Mizia, J.
Powiązania:
https://bibliotekanauki.pl/articles/1537008.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Lp
Opis:
We analyze the influence of hopping interaction on magnetic ordering. Scattering scheme of the Hubbard III approximation with included inter-site kinetic electron-electron correlation is used. The hopping interaction and inter-site correlation lead to two spin dependent effects: the band width correction and the band-shift correction. The band-shift correction factor causes an exchange splitting between the spin-up and spin-down spectrum, and its role is similar to the exchange interaction in the classic Stoner model. The spin dependent band width correction enhanced strongly by the inter-site kinetic correlation lowers the kinetic energy of electrons by decreasing the majority spin band width for some electron occupations with respect to the minority spin band width. The results show that in the case of the symmetrical density of states there is only ferromagnetic enhancement. For the strongly asymmetrical density of states there is a ferromagnetic transition.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 336-339
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Structure and Magnetic Properties of Intermetallic Alloys
Autorzy:
Jezierski, A.
Pugacheva, M.
Morkowski, J. A.
Szajek, A.
Powiązania:
https://bibliotekanauki.pl/articles/1953169.pdf
Data publikacji:
1997-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.-b
75.10.Lp
Opis:
We present the influence of local ordering on the electronic and magnetic properties of Heusler-type alloys. The band structure and magnetic moments are calculated by ab initio spin-polarized tight binding linear muffin-tin orbital method. The calculated electronic density of states for Pd$\text{}_{2}$TiAl alloy is similar to ultraviolet photoelectron spectroscopy measurements. The self-consistent band calculations showed that the density of states at the Fermi level in Ni$\text{}_{2}$(Nb$\text{}_{(1-x)}$Ti$\text{}_{x}$)Sn and Ni$\text{}_{2}$(Nb$\text{}_{(1-x)}$Ta$\text{}_{x}$)Sn alloys decreased with the increase in Ti or Ta concentration. The total and local magnetic moments in ordered Rh$\text{}_{2}$TMSn (TM = Mn, Fe, Co, Ni, Cu) and Rh$\text{}_{2}$MnX (X = Al, Ga, In, Ge, Sb, Pb) Heusler-type alloys are calculated. The difference between theoretical and experimental results can be connected to the partial disorder in the samples.
Źródło:
Acta Physica Polonica A; 1997, 91, 1; 151-159
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetism Within the Limitations of the LDA Band Structure Calculations
Autorzy:
Szpunar, B.
Powiązania:
https://bibliotekanauki.pl/articles/1929380.pdf
Data publikacji:
1993-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.25.-s
75.10.Lp
Opis:
We discuss the limitations of the local density approximation for high-temperature superconductors and related to them parent antiferromagnetic insulators. The calculated band-gap accuracy is pointed out for two cases: C$\text{}_{60}$-FCC and YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6}$. We also compare the results for parent CaCuO$\text{}_{2}$ and NiO systems, as well as discuss the role of gradient and self-energy (GW) corrections for the Mott insulators.
Źródło:
Acta Physica Polonica A; 1993, 84, 1; 21-42
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Strongly Correlated Electrons in a Magnetic Field: Fermi Liquid versus Spin Liquid
Autorzy:
Spałek, J.
Wójcik, W.
Powiązania:
https://bibliotekanauki.pl/articles/1930575.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.28.-d
75.10.Lp
Opis:
We compare the Fermi liquid (FL) and statistical spin liquid (SSL) representations of the electronic properties for strongly correlated systems. In particular, we discuss the entropy, as well as the magnetization as a function of band filling, temperature and magnetic field. These properties are quite different in the two (FL, SSL) states. Antiferromagnetic state disappears for a small number of holes in the doped Mott insulator.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 357-361
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 54

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