Triplet spin resonance of the Haldane compound with interchain coupling

Spin resonance absorption of the triplet excitations is studied experimentally in the Haldane magnet PbNi2V2O8. The spectrum has features of spin S=1 resonance in a crystal field, with all three components, corresponding to transitions between spin sublevels, being observable. The resonance field is temperature dependent, indicating the renormalization of excitation spectrum in interaction between the triplets. Magnetic resonance frequencies and critical fields of the magnetization curve are consistent with a boson version of the macroscopic field theory [Affleck 1992, Farutin & Marchenko 2007], implying the field induced ordering at the critical field, while contradict the previously used approach of noninteracting spin chains.Comment: 7 pages, 9 figure

NMR study of the high-field magnetic phase of LiCuVO4_4

We report on NMR studies of the quasi--1D antiferromagnetic $S=1/2$ chain cuprate LiCuVO$_4$, focusing on the high--field spin--modulated phase observed recently in applied magnetic fields $H > H_{\rm c2}$ ($\mu_0H_{\rm c2} \approx 7.5$ T). The NMR spectra of $^7$Li and $^{51}$V around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin--modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the {\bf ab}--plane at low temperatures 0.6 K $< T < T_{\rm N}$. The best fit provides evidence that the mutual orientation between spins of neighboring {\bf ab}--planes is random. For elevated temperatures $T_{\rm N} < T \lesssim 15$ K, short--range magnetic order occurs at least on the characteristic time scale of the NMR experiment.Comment: 5 pages, 5 figure

Spin-modulated quasi-1D antiferromagnet LiCuVO_4

We report on magnetic resonance studies within the magnetically ordered phase of the quasi-1D antiferromagnet LiCuVO_4. Our studies reveal a spin reorientational transition at a magnetic field H_c1 ~ 25 kOe applied within the crystallographical (ab)-plane in addition to the recently observed one at H_c2 \~75 kOe [ M.G. Banks et al., cond-mat/0608554 (2006)]. Spectra of the antiferromagnetic resonance (AFMR) along low-frequency branches can be described in the frame of a macroscopic theory of exchange-rigid planar magnetic structures. These data allow to obtain the anisotropy of the exchange interaction together with a constant of the uniaxial anisotropy. Spectra of 7Li nuclear magnetic resonance (NMR) show that, within the magnetically ordered phase of LiCuVO_4 in the low-field range H < H_c1, a planar spiral spin structure is realized with the spins lying in the (ab)-plane in agreement with neutron scattering studies of B.J. Gibson et al. [Physica B Vol. 350, 253 (2004)]. Based on NMR spectra simulations, the transition at H_c1 can well be described as a spin-flop transition, where the spin plane of the magnetically ordered structure rotates to be perpendicular to the direction of the applied magnetic field. For H > H_c2 ~ 75 kOe, our NMR spectra simulations show that the magnetically ordered structure exhibits a modulation of the spin projections along the direction of the applied magnetic field H

High-Field Low-Frequency Spin Dynamics

The theory of exchange symmetry of spin ordered states is extended to the case of high magnetic field. Low frequency spin dynamics equation for quasi-goldstone mode is derived for two cases of collinear and noncollinear antiferromagnets.Comment: 2 page

Structure and Properties of Nanocomposite Coatings Based on Titanium, Oxygen, Carbon and Hydrogen Obtained by the Cumulative-Detonation Device

Nanocomposite coatings based on Ti, O, C and H thickness of 70 – 200 microns with hardness of 1015 250 HV0.05 and porosity 2 – 5% were deposited on aluminium samples by using the cumulativedetonation equipment. The nanocomposite coatings were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with diffraction, X-ray phase analysis, hardness measurements. It is shown that the area of the coating that adjoins to the substrate contains a transition layer of intermetallic TiAl and the nanocomposite coatings based on Ti, O, C and H are characterized by the presence of titanium nanocrystalline grains with face-centered close-packed lattice, amorphous phases and nanoamorphous oxide of titanium. It was found that the main phases of the composite coatings are Ti, TiO, rutile, anatase, Ti2O3. In the composite coatings formed from the hydrogenated powder was recorded the presence of -TiH phase and TiH2. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3488

Magnetic structure of the frustrated S=1/2 chain magnet LiCu2O2 doped with nonmagnetic Zn

We present the results of magnetization, ESR and NMR measurements on single crystal samples of the frustrated S=1/2 chain cuprate LiCu2O2 doped with nonmagnetic Zn^2+. As shown by the x-ray techniques the crystals of Li(Cu{1-x}Zn{x})2O2 with x<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 Cu^2+ ions in this structure is close to value obtained for undoped crystals: (0.8 +- 0.1) mu_B.Comment: 12 pages, 10 figure

The Wear Resistance of the Nanocomposite Coatings Obtained by the Cumulative- Detonation Device

Nanocomposite coatings based on Ti, O, C and H were deposited on aluminium samples by using the cumulative-detonation equipment. The nanocomposite coatings were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with diffraction, X-ray phase analysis, hardness measurements and tribotests. It was established that the wear of nanocomposite coatings based on Ti, O, C and H less than to the wear of material of the substrate. For the nanocomposite coating which were formed from the hydrogenated titanium powder was recorded the lowest wear and coefficient of friction. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3515