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Tytuł:
Surface Effects in Spin-Wave Spectrum of the Semi-Infinite FeBr$\text{}_{2}$ Field-Induced Metamagnet
Autorzy:
Rudziński, W.
Maciejewski, W.
Powiązania:
https://bibliotekanauki.pl/articles/1930606.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.30.Kz
Opis:
Surface spin waves in the layered structure of the FeBr$\text{}_{2}$ field-induced metamagnet are studied theoretically. Surface spin-wave modes are calculated for the (001) surface and for the paramagnetic phase at low temperatures. Allowing the surface exchange parameters to deviate from the bulk values, full richness of the surface spin-wave spectra is displayed. The problem of the stability of the ground state of the system is also discussed.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 433-437
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Are there optical magnons?
Autorzy:
Köbler, U.
Powiązania:
https://bibliotekanauki.pl/articles/1048212.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.30.Et
Opis:
Optical magnons should occur in magnets containing two in-equivalent magnetic species only. However, Heisenberg interactions between in-equivalent magnetic atoms can be expected to be weak. This is because free exchange of electrons between chemically different magnetic atoms appears not generally possible. To the best of our knowledge optical magnons have never been identified unambiguously experimentally. Confusion is provided by the fact that two magnon branches commonly occur in antiferromagnets with ferromagnetically ordered crystallographic planes and opposite spin orientations from plane to plane. This applies to MnO, EuTe, CoCl₂, Fe₂O₃, K₂FeF₄. Associated with the ferromagnetic planes is a particular low-energy magnon branch. The high-energy magnon branch is the antiferromagnetic branch and not an optical magnon. In Fe₃O₄ (magnetite), weak interactions between the Fe²⁺ moments and the Fe³⁺ moments are evidenced by the fact that the order parameters of the FeO and of the Fe₂O₃ subsystem have different temperature dependencies. The observed two magnon branches can be attributed to the Fe₂O₃ and to the FeO subsystem, respectively. This applies equally to the two observed magnon branches in mixed crystals such as Rb₂Mn_{0.5}Ni_{0.5}F₄, KCo_{0.71}Mn_{0.29}F₃ or Mn_{0.3}Co_{0.7}F₂ that can be understood as modified dispersions of the constituent materials.
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 459-462
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:
Temperature Dependence of Magnetic Inelastic Neutron Scattering in Mn(12%Ge) Alloy
Autorzy:
Jankowska-Kisielińska, J.
Mikke, K.
Milczarek, J. J.
Hennion, B.
Udovenko, V. A.
Powiązania:
https://bibliotekanauki.pl/articles/1956523.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.50.Ee
Opis:
A systematic study of temperature dependence of magnetic inelastic neutron scattering for itinerant antiferromagnet Mn(12%Ge) is presented. At low temperatures the experimental data are well described in terms of damped spin waves. This description becomes insufficient at least 150 K below T$\text{}_{N}$. In the temperature range 200-400 K the integrated intensity of distribution for energy transfer 13 THz increases by one third and the shape of the deconvoluted neutron scattering cross-section changes. These changes suggest that ca. 200 K below T$\text{}_{N}$ an additional contribution to the inelastic neutron scattering starts to appear and that its origin is different from spin waves.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 483-486
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Wave Resonance in the FeBr$\text{}_{2}$ Metamagnetic Thin Film
Autorzy:
Rudziński, W.
Powiązania:
https://bibliotekanauki.pl/articles/2013141.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.70.Ak
Opis:
The spin-wave resonance in the thin FeBr$\text{}_{2}$ field-induced metamagnet in the paramagnetic phase with the (001) surfaces and at low temperatures is examined theoretically. It is found that the absorption spectrum is strongly affected by modifications of the surface exchange parameters. Also, the conditions for the appearance of various surface and bulk spin-wave features are discussed.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 503-506
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Interface Effective Pinning and Dynamical Coupling of Spin Waves in Bilayer Ferromagnetic Films with Canted Magnetizations
Autorzy:
Puszkarski, H.
Cottam, M. G.
Powiązania:
https://bibliotekanauki.pl/articles/1887424.pdf
Data publikacji:
1991-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.70.Cn
Opis:
We present a theory for the spin-wave excitations in bilayer magnetic systems with exchange coupling across the interface between two ferromagnetic films having the same crystallographic structure. The Hamiltonian includes exchange and anisotropy terms within each magnetic film of the composite system, as well as at the interface and at the free surfaces. We examine, in particular, the effect of interface canting between the magnetization directions for each film, and we derive effective pinning parameters and dynamic coupling parameters for the interface as functions of the canting angle. We show that, in the special case when the magnetization directions are antiparallel in the bilayer system, the two films may be considered as effectively decoupled as regards the spin-wave dynamics. We discuss the relevance of this theory to recent experimental studies of bilayer ferromagnetic systems that exhibit antiferromagnetic interface exchange.
Źródło:
Acta Physica Polonica A; 1991, 79, 4; 549-564
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hybridization of Surface and Impurity Spin Waves Induced by their Propagation in the Plane of a Thin Ferromagnetic Film
Autorzy:
Kołodziejczak, B.
Puszkarski, H.
Powiązania:
https://bibliotekanauki.pl/articles/1891796.pdf
Data publikacji:
1991-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.70.-i
Opis:
Spin waves of a thin ferromagnetic film containing in its bulk two impurity layers, each parallel to the film surface and symmetrically disposed with regard to the film centre, are theoretically investigated within the framework of the Heisenberg model. The existence conditions for surface-localized and impurity-layer localized spin waves are established. Particular attention is given to the effect of a possible hybridization of these localized excitations; it is shown that this phenomenon does in fact occur for certain specified directions of the in-plane wave vector k$\text{}_{||}$.
Źródło:
Acta Physica Polonica A; 1991, 80, 5; 675-687
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Brillouin Zone Mapping of the Existence Conditions for Interface Bilayer Spin-Waves. Effects of the Configuration of the Film Magnetization
Autorzy:
Puszkarski, H.
Józefowicz, R.
Kołodziejczak, B.
Akjouj, A.
Djafari-Rouhani, B.
Dobrzynski, L.
Powiązania:
https://bibliotekanauki.pl/articles/1945427.pdf
Data publikacji:
1996-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.70.Cn
Opis:
For the two interface cubic cuts: sc(110) and sc(111) we consider the existence regions of interface spin-waves of a ferromagnetic bilayer film on the two-dimensional Brillouin zone as to their size and shape versus the respective interface related parameters (interface exchange coupling and intrinsic interface anisotropy) applying the approximation of a very thick bilayer film and the method of Brillouin zone mapping (the three (100) interface cubic orientations have been dealt with earlier [Phys. Rev. B 51, 16008 (1995)]). Of particular interest to us still remains the emergence of interface spin-waves induced by varying dynamic quantities such as the in-plane propagation wave vector k$\text{}_{∥}$. Moreover, in our present investigation, we put especial emphasis on the effect exerted on the Brillouin zone mapping by varying (in the plane perpendicular to the film) the configuration angle of the film magnetization with respect to the film normal. We predict the existence of (at the most two) critical angles $\text{}_{c}$ at which the interface spin-waves emerge. These critical angles are functions of the in-plane wave vector k$\text{}_{∥}$ of interface spin-wave propagation along the interface. Finally, we discuss the effects due to the presence of critical angles with a view to their exploitation in experimental measurements.
Źródło:
Acta Physica Polonica A; 1996, 89, 5-6; 675-688
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Two-Dimensional Brillouin Zones in Thin Magnetic Films and a Mapping of the Regions of Existence of Magnetic Surface States
Autorzy:
Kołodziejczak, B.
Puszkarski, H.
Powiązania:
https://bibliotekanauki.pl/articles/1929326.pdf
Data publikacji:
1993-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.70.-i
Opis:
We consider the model of a thin ferromagnetic film, described by a standard Heisenberg Hamiltonian involving interactions between nearest neighbours. The surface inhomogeneities are introduced by means of "surface parameters" describing strictly the conditions at the surfaces. We consider the surface orientations SC(111) and FCC(111), for which we diagonalize the Hamiltonian by standard procedure obtaining the characteristic equation for the permitted eigenvalues (and eigenvectors perpendicular to the surface) versus the two-dimensional wave vector in the plane of the reciprocal lattice. It is found that the existence of a surface state (at fixed surface conditions) requires an appropriate propagation direction of the spin wave in the plane of the film. This requirement is visualized graphically by plotting the existence regions of the surface states in the two-dimensional Brillouin zone. These regions are studied as to their form and size versus the surface parameters. For the two surface orientations studied, the existence regions are found to be identical and hence they are not sensitive to the differences in cubic structure between SC and FCC.
Źródło:
Acta Physica Polonica A; 1993, 83, 5; 661-676
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:
Weak Ferromagnetism in the Helimagnet $Ba_{2}CuGe_{2}O_{7}$
Autorzy:
Chovan, J.
Marder, M.
Papanicolaou, N.
Powiązania:
https://bibliotekanauki.pl/articles/1366485.pdf
Data publikacji:
2014-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.30.Ds
75.30.Gw
75.30.Kz
Opis:
The Dzyaloshinskii-Moriya anisotropy, responsible for helimagnetism in $Ba_{2}CuGe_{2}O_{7}$, has recently been shown to comprise also a weak-ferromagnetic component. We theoretically demonstrate the signatures of weak-ferromagnetism in the magnon spectrum when a magnetic field is applied perpendicular to the z axis. We also anticipate the occurrence of unconventional domain walls in the so-called intermediate phase, and briefly elucidate the importance of the weak ferromagnetic component of the Dzyaloshinskii-Moriya anisotropy for the dynamics of driven domain walls.
Źródło:
Acta Physica Polonica A; 2014, 126, 1; 32-33
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Fracton Excitations in the Magnetic "Net Fractal" Systems
Autorzy:
Bąk, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1813878.pdf
Data publikacji:
2008-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.43.Hv
75.30.Ds
Opis:
A localized spin system of fractal symmetry and Heisenberg exchange between nearest neighbors is considered. We define a specific class of fractals: "net fractals" and prove that in the logarithmic scale they are isomorphic with some bulk crystals. Further, with the use of logarithmic coordinates we show that the "net fractal" magnetic fractons can be presented as the conventional magnons.
Źródło:
Acta Physica Polonica A; 2008, 113, 1; 541-544
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The J₁-J₂ Model on the Anisotropic Triangular and the Square Lattice: Similarities and Differences
Autorzy:
Schmidt, B.
Thalmeier, P.
Powiązania:
https://bibliotekanauki.pl/articles/1385520.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.30.Cr
75.30.Ds
Opis:
The Heisenberg model on a triangular lattice is a prime example for a geometrically frustrated spin system. However most experimentally accessible compounds have spatially anisotropic exchange interactions. As a function of this anisotropy, ground states with different magnetic properties can be realized. On the other hand, the J₁-J₂ model on the square lattice is a well-known example for frustration induced by competing exchange. The classical phase diagrams of the two models are related in a broad range of the control parameter ϕ=$tan^{-1}$(J₂/J₁). In both cases three different types of ground states are realized, each model having a ferromagnetic and an antiferromagnetic region in the phase diagram, and a third phase with columnar magnetic order for the square lattice and an in general incommensurate spiral structure for the triangular lattice. Quantum effects lift degeneracies in the non-FM phases and lead to additional nonmagnetic regions in the phase diagrams. The contribution of zero point fluctuations to ground state energy, wave vector, and ordered moment is discussed.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 324-326
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 86

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