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Spin Quantum Numbers (spin + quantum_number)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Four-sublattice ferrimagnetic systems: II.

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
Effects of the spin quantum number
Abstract The effects of the spin quantum number of each sublattice on the quantum fluctuations are discussed for different spin configurations in four-sublattice ferrimagnetic systems. In multi-sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate spin direction, equals to that of sites with opposite initiate spin direction ,i , = ,j ,, i and j denote respectively the spins along the up and down initiate spin directions). The role of the spin quantum number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the spin quantum number of each sublattice and the magnetically structural symmetry of the system all play important roles on the quantum fluctuations of the systems. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnets

ANNALEN DER PHYSIK, Issue 10-11 2009
B. Vogt
Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source]

Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnets

ANNALEN DER PHYSIK, Issue 10-11 2009
B. Vogt
Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source]

Spin-wave spectra and magnetization of ferro,ferrimagnetic double layers

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008
Wei Jiang
Abstract The spin-wave spectra and magnetization of the ferro,ferrimagnetic double layers are studied by using a linear spin-wave approximation and retarded Green's-function method. We obtain the four branches of the spin-wave spectra. Two energy gaps are found to exist in the energy band. The effects of the interlayer exchange coupling, the intralayer exchange coupling and the spin quantum numbers on the spin-wave spectra and the energy gaps are discussed. The minimum (maximum) value point on the spin-wave spectra and energy gaps correspond to a system that has a high symmetrical magnetic structure and the balance of quantum competitions among the exchange couplings and the spin quantum numbers of the system. There is a crossover between sublattice magnetizations in ferromagnetic layer that is affected by quantum fluctuations, thermal fluctuations and frustration of spins. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnon energy gap and the magnetically structural symmetry in a three-layer ferrimagnetic superlattice

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006
Rong-ke Qiu
Abstract The magnon energy band in a ferrimagnetic superlattice with three layers in a unit cell is studied by employing retarded Green's functions and the spin-wave method. Two modulated energy gaps ,,13 and ,,23 are evaluated systematically, which exist in the magnon energy band along the Kx -direction perpendicular to the plane of the superlattice. It is revealed that the energy gap ,,13 has a direct relation with the symmetry among the spin quantum numbers and the interlayer exchange couplings, while the energy gap ,,23 relates to the symmetry among these spin quantum numbers only. These symmetries differ from the symmetry of crystallographic point groups. We define the magnetically structural symmetry that is dominated mainly by the magnetic parameters. The absence of the energy gap at a certain condition means that the system has a high magnetically structural symmetry. The magnetically structural symmetry of the superlattice, which is an intrinsic property, strongly affects the magnon energy band structure and thus the magnetic behaviors of the system. Furthermore, two complete bandgaps are observed to extend through the Brillouin zone (referred to as "magnonic crystal") in this superlattice system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnets

ANNALEN DER PHYSIK, Issue 10-11 2009
B. Vogt
Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source]

Reduction of quantum fluctuations by anisotropy fields in Heisenberg ferro- and antiferromagnets

ANNALEN DER PHYSIK, Issue 10-11 2009
B. Vogt
Abstract The physical properties of quantum systems, which are described by the anisotropic Heisenberg model, are influenced by thermal as well as by quantum fluctuations. Such a quantum Heisenberg system can be profoundly changed towards a classical system by tuning two parameters, namely the total spin and the anisotropy field: Large easy-axis anisotropy fields, which drive the system towards the classical Ising model, as well as large spin quantum numbers suppress the quantum fluctuations and lead to a classical limit. We elucidate the incipience of this reduction of quantum fluctuations. In order to illustrate the resulting effects we determine the critical temperatures for ferro- and antiferromagnets and the ground state sublattice magnetization for antiferromagnets. The outcome depends on the dimension, the spin quantum number and the anisotropy field and is studied for a widespread range of these parameters. We compare the results obtained by: Classical Mean Field, Quantum Mean Field, Linear Spin Wave and Random Phase Approximation. Our findings are confirmed and quantitatively improved by numerical Quantum Monte Carlo simulations. The differences between the ferromagnet and antiferromagnet are investigated. We finally find a comprehensive picture of the classical trends and elucidate the suppression of quantum fluctuations in anisotropic spin systems. In particular, we find that the quantum fluctuations are extraordinarily sensitive to the presence of small anisotropy fields. This sensitivity can be quantified by introducing an "anisotropy susceptibility". [source]