Phase diagram of low-dimensional antiferromagnets with competing order parameters: A Landau-theory approach
We present a detailed analysis of the phase diagram of antiferromagnets with competing exchange-driven and field-induced order parameters. By using the quasi-1D antiferromagnet BaCu2Si2O7 as a test case, we demonstrate that a model based on a Landau type of approach provides an adequate description of both the magnetization process and of the phase diagram. The developed model not only accounts correctly for the observed spin-reorientation transitions, but it predicts also their unusual angular dependence.
We report on a heat-capacity study of high-quality single-crystal samples of LiCuVO4 - a frustrated spin S=1/2 chain system - in a magnetic field amounting to 3/4 of the saturation field. A detailed examination of magnetic phase transitions observed in this field range shows that although the low-field helical state clearly has three-dimensional properties, the field-induced spin-modulated phase turns out to be quasi-two-dimensional. The model proposed in this paper allows one to qualitatively understand this crossover, thus eliminating the presently existing contradictions in the interpretations of NMR and neutron-scattering measurements.
We report results of an electron spin resonance (ESR) study of a spin-gap antiferromagnet (C4H12N2)(Cu2Cl6) (nicknamed PHCC) with chlorine ions partially substituted by bromine. We found that up to 10% of nominal doping the contribution of the random defects to the absorption spectra remains at about 0.1% per copper ion, which is almost the same as in the pure system. Instead, a particular kind of ESR absorption corresponding to gapless S = 1 triplets is observed at low temperatures in samples with high nominal bromine content x 5%. Increase of bromine concentration also leads to the systematic broadening of ESR absorption line, indicating reduction of the quasi-particles lifetime.
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 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.