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Wyświetlanie 1-15 z 58
Tytuł:
Spin-1/2 Periodic Nonuniform XX Chains and the Spin-Peierls Instability
Autorzy:
Derzhko, O.
Richter, J.
Zaburannyi, O.
Powiązania:
https://bibliotekanauki.pl/articles/2013736.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
Opis:
Using continued fractions we obtained the exact result for the density of magnon states of the regularly alternating spin-1/2 XX chain with the Dzyaloshinskii-Moriya interaction. We examined the stability of the magnetic chain with respect to the spin-Peierls dimerization.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 931-934
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Phase Diagram of Two-Axis Ferromagnet and Spectra of Coupled Magnetoelastic Waves
Autorzy:
Mitsay, Yu. N.
Fridman, Yu. A.
Kozhemyako, O. V.
Kochmański, M. S.
Powiązania:
https://bibliotekanauki.pl/articles/2011089.pdf
Data publikacji:
1999-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
Opis:
The phase diagram of strongly anisotropic two-axis ferromagnet at arbitrary orientation of external magnetic field is built. It is demonstrated that together with a ferromagnetic phase there is possible the existence of phases with a tensorial order parameter: quadrupolar or quadrupolar-ferromagnetic phases. Spectra of bound magnetoelastic waves are investigated. Besides it is demonstrated that at large enough magnetoelastic interaction there is possible an active interaction of a magnetic subsystem with longitudinally polarized acoustic mode which becomes a soft mode at the point of orientational phase transition.
Źródło:
Acta Physica Polonica A; 1999, 96, 3-4; 445-456
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ground State and Magnetostatic Properties of a Dipole System Arranged in Two-Dimensional Lattice
Autorzy:
Bolcal, E.
Dimitrov, V.
Aktaş, B.
Aslan, H.
Bozkurt, A.
Powiązania:
https://bibliotekanauki.pl/articles/1491456.pdf
Data publikacji:
2012-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
Opis:
A system of nano sized modomain ferromagnetic particle arranged in two-dimensional lattice is theoretically investigated. The basic aim of the investigation is to find the ground state of these types of models where the interaction is long-ranged and anisotropic. The numerical calculations show that for some lattices there is a number of degenerated states near the zero temperature. The ground state of these systems is basically of a complicated antiferromagnetic type.
Źródło:
Acta Physica Polonica A; 2012, 121, 1; 257-261
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
One-Dimensional Boson Fields in the Critical Range of EuS and EuO
Autorzy:
Köbler, U.
Powiązania:
https://bibliotekanauki.pl/articles/1401902.pdf
Data publikacji:
2015-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.30.Ds
Opis:
Following the principles of renormalization group theory the typical experimental indications are discussed that in ordered magnets with a three-dimensional spin the dynamics of the spins is controlled by a boson guiding field instead by exchange interactions to the neighboring spins. The spins are, so to say, sensors to probe the dynamics of the relevant boson field. It is evident that these findings are not complementary but fundamentally different from atomistic concepts. The bosons are essentially magnetic dipole radiation emitted upon precession of the ordered moments. Within the individual domain the one-dimensional field has the character of a laser field. The field aligns all spins along its axis. In order that in cubic magnets three-dimensional dynamic symmetry can result a vector average over all one-dimensional boson fields of the individual domains is necessary. It is argued that this averaging process does not work in the critical temperature range of cubic EuS and EuO. As a result, the critical behavior of EuS and EuO is that of the one-dimensional boson field of the isolated domain and agrees with the critical behavior of the one-dimensional antiferromagnet MnF₂. For the magnets with 1D boson field and half-integer spin it is found that the rational exponents β = 1/3, γ = 4/3 and ν = 2/3 give an excellent account of the mean exponent values over the most accurately known experimental data. These exponents obey the scaling relation 2β = 3ν - γ .
Źródło:
Acta Physica Polonica A; 2015, 128, 3; 398-407
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Boson Fields in Ordered Magnets
Autorzy:
Hoser, A.
Köbler, U.
Powiązania:
https://bibliotekanauki.pl/articles/1385608.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.30.Ds
Opis:
Spin wave theory of magnetism reveals two severe shortcomings. First, it considers non quantized classical spins and, second, the predicted temperature power functions for the thermal decrease of the magnetic order parameter hold asymptotically at T = 0 only. As experiments unambiguously show the dynamics is different for magnets with integer and half-integer spin and the "critical" power functions at T = 0 of type ΔM ≈ $T^{ε}$ or at T = $T_{c}$ of type ≈$(T_{c}-T)^β$ hold over a finite temperature range, independent of spin structure. The finite critical range unequivocally indicates that the dynamics of the spins is controlled by a field of freely propagating bosons instead by exchange interactions. Consequently, field theories are necessary for description of the thermodynamics of ordered magnets. The experimental indications will be discussed that the field quanta are essentially magnetic dipole radiation emitted by the precessing magnetic moments. Since integer and half-integer spins precess differently the generated field quanta and the dynamics of the field are correspondingly different.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 350-352
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Interaction by Exchange of Field Bosons
Autorzy:
Köbler, U.
Hoser, A.
Powiązania:
https://bibliotekanauki.pl/articles/1427529.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.30.Ds
Opis:
It is shown that atomistic spin wave theory gives no correct account of the temperature dependence of the magnetic order parameter. The experimentally observed universal temperature dependence can be explained only by a field theory of magnetism. This means that instead by interacting spins (magnons) the dynamics is controlled by a boson field. The field quanta can be supposed to be magnetic density waves with dispersions that are simple power function of wave vector. This results in the observed universality. In three dimensions the field quanta have no mass and linear dispersion and cannot be observed using inelastic neutron scattering. Experiments on standing magnetic waves in thin ferromagnetic films provide direct information on the dispersion of the field quanta. A careful analysis of the available experimental data indicates that the dispersion of the field bosons is ım q, ım $q^2,$ and ım $q^{3//2}$ in three, two, and one dimensions.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1176-1178
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dimensionality in Field Theory and in Spin Wave Theory
Autorzy:
Köbler, U.
Hoser, A.
Powiązania:
https://bibliotekanauki.pl/articles/1385629.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.30.Ds
Opis:
The different meaning of dimensionality and universality in field theory and in spin wave theory is illustrated on account of experimental examples. In spin wave theory it is distinguished between the dimensionality of the spin and the dimensionality of the exchange interactions. According to Renormalization Group (RG) theory, these atomistic characteristics are unimportant for the critical dynamics. Instead by inter-atomic interactions the dynamics of the ordered state is determined by the excitations of the continuous magnetic medium. These excitations are bosons. Consequently, the dimensionality of ordered magnets has to be assessed to the dimensionality of the relevant boson field. The most serious consequence of RG theory is that the magnetic ordering transition also is executed by the boson field. Typical for boson dynamics is a finite width of the critical range. In the atomistic models universality applies asymptotically at $T_{c}$ only. It is evident that the critical power functions of the field dynamics are different from those of the atomistic dynamics.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 356-358
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of a One-Ion Anisotropy on Stabilization of the Long-Range Magnetic Order in Two-Dimensional Ferromagnet
Autorzy:
Mitsay, Yu. N.
Fridman, Yu. A.
Spirin, D. V.
Kochmański, M. S.
Powiązania:
https://bibliotekanauki.pl/articles/2012959.pdf
Data publikacji:
2000-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.30.Kz
Opis:
In the paper the possibility of stabilization of the long-range magnetic order in a two-dimensional ferromagnetic with one-ion easy-plane anisotropy is explored. It is shown that at the presence of a small anisotropy in a two-dimensional ferromagnetic the long-range magnetic order is stabilized by magnetoelastic interaction. If one-ion anisotropy is comparable or even exceeds the exchange interaction in the system there exists a long-range non-vectorial quadrupolar tensorial magnetic order.
Źródło:
Acta Physica Polonica A; 2000, 97, 2; 355-360
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Magnetic Specific Heat of the BEG Model
Autorzy:
Gzik-Szumiata, M.
Balcerzak, T.
Powiązania:
https://bibliotekanauki.pl/articles/2013966.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.70.-i
Opis:
The magnetic contribution to the specific heat of the Blume-Emery-Griffiths model with spin-one is studied by the cluster variational method in pair approximation. The nearest neighbour correlation functions are taken into account. The temperature dependencies of the specific heat are calculated and discussed in the context of the phase diagrams obtained recently for the thin film with bilayer geometry.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 939-942
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Specific Heat and the Ground State of NiO
Autorzy:
Radwanski, R.
Ropka, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1812327.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.-w
75.10.-b
75.10.Dg
Opis:
Working in the strongly-correlated crystal-field approach and in the strong hybridization limit we calculated the temperature dependence of the heat capacity of NiO in a wide temperature range, from zero temperature to 1200 K. Our calculations reproduce reasonably well experimental dependence including the λ-type peak at $T_N$ of 525 K.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 213-217
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Differential Operator Technique in the Ising Spin Systems
Autorzy:
Kaneyoshi, T.
Powiązania:
https://bibliotekanauki.pl/articles/1929335.pdf
Data publikacji:
1993-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
75.10.-b
Opis:
A review is given of the differential operator technique in the Ising spin systems. The theoretical frameworks of the various models are discussed on the basis of the Ising spin identities. These can be applied to examine the magnetic properties in a variety of magnetic materials.
Źródło:
Acta Physica Polonica A; 1993, 83, 6; 703-738
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
EPR Spectra of Multispin Systems. Application to Poly-m-p-Aniline
Autorzy:
Juszyński, P.
Twardowski, A.
Gosk, J.
Kulszewicz-Bajer, I.
Pawłowski, M.
Dziatkowski, K.
Szczytko, J.
Powiązania:
https://bibliotekanauki.pl/articles/2048138.pdf
Data publikacji:
2011-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
02.70.-c
75.10.-b
Opis:
In this communication we present NiceMagnetic, software for simulations and analysis of EPR spectrum and SQUID measurements. Systems of arbitrary number N of spin-only magnetic moments (S ≤ 0 and L = 0) were considered within the lines of the Heisenberg and Zeeman Hamiltonians. Effective algorithms used for the computations are discussed. This includes modified secant method adapted to calculate resonance fields with demanded precision. Finally, application of NiceMagnetic to experimental SQUID magnetization and EPR spectra of poly-m-p-aniline, one of recently synthesized high spin polymers containing unpaired electrons will be presented. As a result, exchange integral between electron and nitrogen nuclei spins (ligand hyperfine interaction) J = 6.3 × 10$\text{}^{-4}$ cm$\text{}^{-1}$ was estimated.
Źródło:
Acta Physica Polonica A; 2011, 119, 5; 717-719
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The "Higgs" Amplitude Mode in Weak Ferromagnetic Metals
Autorzy:
Zhang, Yi
Farinas, P.
Bedell, K.
Powiązania:
https://bibliotekanauki.pl/articles/1383968.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
71.10.Ay
75.50.Cc
Opis:
Using ferromagnetic Fermi liquid theory, Bedell and Blagoev derived the collective low-energy excitations of a weak ferromagnet. They obtained the well-known magnon (Nambu-Goldstone) mode and found a new gapped mode that was never studied in weak ferromagnetic metals. In this article we have identified this mode as the Higgs boson (amplitude mode) of a ferromagnetic metal. This is identified as the Higgs since it can be shown that it corresponds to a fluctuation of the amplitude of the order parameter. We use this model to describe the itinerant-electron ferromagnetic material MnSi. By fitting the model with the existing experimental results, we calculate the dynamical structure function and see well-defined peaks contributed from the magnon and the Higgs. Our estimates of the relative intensity of the Higgs amplitude mode suggest that it can be seen in neutron scattering experiments on MnSi.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 153-156
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Neural Network Model of an Ising Spin Glass
Autorzy:
Wilson, K. F.
Goossens, D. J.
Powiązania:
https://bibliotekanauki.pl/articles/2013998.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.10.Nr
84.35.+i
Opis:
The behaviour of an Ising spin glass (S=1/2) with infinite range interactions is modelled using a numerical simulation based on a neural network. Thermodynamic variables are defined on the network, and are found to obey the Thouless-Anderson-Palmer theory when the applied magnetic field is zero. When a magnetic field is applied along the spin direction, complex field-dependent behaviour appears, including a state in which the Edwards-Anderson order parameter is independent of temperature below the critical temperature.
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 983-986
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Threefold Symmetric Magnetic Two-Ion Coupling in hcp Rare-Earth Metals
Autorzy:
Jensen, J.
Powiązania:
https://bibliotekanauki.pl/articles/1953160.pdf
Data publikacji:
1997-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Gw
75.10.-b
75.25.+z
Opis:
The heavy rare earths crystallize in the hcp structure. Most of the magnetic couplings between two ions in these metals are independent of the two different orientations of the hexagonal layers. However, trigonal anisotropy terms may occur, reflecting that the c-axis is only a threefold axis. In the presence of a trigonal coupling the symmetry is reduced, and the double-zone representation in the c-direction ceases to be valid. The strong interaction between the transverse optical phonons and the acoustic spin waves propagating in the c-direction of Tb detected more than twenty years ago, was the first example of a trigonal coupling found in these systems. A few years ago a careful neutron-diffraction study of the c-axis modulated magnetic structures in Er showed the presence of higher harmonics at positions along the c-axis translated by odd multiple of 2π/c. This indicates distortions of the structures due to trigonal couplings, and the same characteristic phenomenon has now also been observed in Ho. Additionally, mean-field calculations show that a trigonal coupling in Ho is required, in order to explain the increase in the commensurable effects observed for the 8 and 10 layered periodic structures, when a field is applied along the c-axis.
Źródło:
Acta Physica Polonica A; 1997, 91, 1; 89-103
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 58

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