Numeric calculation of antiferromagnetic resonance frequencies for the noncollinear antiferromagnet
We present an algorithm for the numeric calculation of antiferromagnetic resonance frequencies for the noncollinear antiferromagnets of general type. This algorithm uses general exchange symmetry approach (Andreev and Marchenko,
Sov. Phys. Usp. 130:39, 1980) and is applicable for description of low-energy dynamics of an arbitrary noncollinear spin structure in weak fields. Algorithm is implemented as a MatLab and C++ program codes, available for download. Program codes are tested against some representative analytically solvable cases.
We present the results of magnetization, electron spin resonance (ESR), and nuclear magnetic resonance (NMR) measurements on single-crystal samples of the frustrated S = 1/2 chain cuprate LiCu2O2 dopedwith nonmagnetic Zn2+.As shown by the x-ray techniques, the crystals of Li(Cu1−xZnx )2O2 withx < 0.12 are single-phase,whereas for higher Zn concentrations the samples were polyphase. ESR spectra for all monophase samples (0 x < 0.12) can be explained within the model of a planar spin structure with a uniaxial type anisotropy. The NMR spectra of the highly doped single-crystal sample Li(Cu0.9Zn0.1)2O2 can be described in the frame of a planar spin-glass-like magnetic structure with short-range spiral correlations in the crystal ab planes with strongest exchange bonds. The value of magnetic moments of Cu2+ ions in this structure is close to the value obtained for undoped crystals: (0.8 ± 0.1) μB.
The electron spin resonance spectrum of a quasi-1D S=1/2 antiferromagnet K2CuSO4Br2 was found to demonstrate an energy gap and a doublet of resonance lines in a wide temperature range between the Curie-Weiss and Neèl temperatures. This type of magnetic resonance absorption corresponds well to the two-spinon continuum of excitations in S=1/2 antiferromagnetic spin chain with a uniform Dzyaloshinskii-Moriya interaction between the magnetic ions. A resonance mode of paramagnetic defects demonstrating strongly anisotropic behavior due to interaction with spinon excitations in the main matrix is also observed.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.