Том 47, № 11 (2016)

The shapes of the spin resonance spectra have been analyzed theoretically in the case, when the kinetic equation for the spin density matrix is linear. Examples of the random relaxation processes which lead to the linear kinetic equations for the spin coherences have been presented in short. A consistent approach has been described for the decomposition of the multicomponent spectra into individual resonance lines based on finding independent collective modes for the evolution of quantum coherences. For the model situations with two and three transitions between the energy levels, the spectra are decomposed following this approach. The contributions of their collective evolution modes to the magnetic resonance spectra have been analyzed comprehensively. In the presence of the coherence transfer, the shapes of resonance lines corresponding to these modes can be a mixture of Lorentzian absorption and dispersion curves. The results obtained make it possible to visualize in detail transformations of the spectra as a consequence of the coherence transfer caused by random relaxation processes. This consistent approach makes it possible to describe on a common platform the transformations of spectra at any coherence transfer rate: from the very slow coherence transfer rate which leads to line broadening, then to the rate which results in the coalescence of the spectral lines and further to the very fast rate which leads to exchange narrowed spectra. It is shown that in the limit of the fast coherence transfer corresponding to the exchange narrowing effect one collective mode gives the dominant contribution to the experimental spectrum, namely, in-phase evolution of all transition coherences. The shape of the resonance corresponding to this in-phase evolution is described by the narrowed Lorentzian absorption curve.

Using the non-equilibrium statistical operator method (NSO), we have investigated the spin transport through the interface in a semiconductor/ferromagnetic insulator hybrid structure. We have analyzed the approximation of effective parameters, when each of the considered subsystems (conduction electrons, magnons, and phonons) is characterized by its effective temperature. We have constructed the macroscopic equations, describing the spin-wave current caused by both resonantly excited spin system of conduction electrons and by an inhomogeneous thermal field in the ferromagnetic insulator. We have shown that the spin-wave current excitation under combined resonance conditions bears a resonant nature.

The short-lived states of the photoexcited conjuncted porphyrin trimer, in which two side zinc porphyrin fragments differ from the central fragment, have been studied by time-resolved continuous-wave and pulse electron paramagnetic resonance (EPR) in X- and Q-bands. It was shown that the observed spectra are the sum of the spectra of two types of porphyrin components. This was particularly evident in the echo-detected spectra at the relatively large time delay between echo-forming microwave pulses when not all the signals were detected due to the anisotropy of phase relaxation times of porphyrin systems. The parameters of the excited triplet states were determined and it was shown that the two types of excited triplet states were characterized by the same values of the g-factors but different values of the zero-field splitting. The anisotropy of the g-tensors of triplet states was estimated from the frequency dependence of the EPR spectra.

Two inequivalent types of hydrogen bonds in KHSO₄ were distinguished at temperatures 180–430 K using single-crystal ¹H nuclear magnetic resonance (NMR) and magic-angle spinning NMR. From the ¹H spin–lattice relaxation time in the laboratory frame, the hydrogen site H(1) with shorter hydrogen bonding is determined to have a longer relaxation time, while the H(2) with longer hydrogen bonds has a shorter relaxation time. The shorter T₁ indicates that the energy transfer from the nuclear spin system to the surrounding environment is more facile.

In this work, the classification of three fuel types (gasoline, diesel, and kerosene) using ¹H nuclear magnetic resonance (NMR) spectroscopy and principal component analysis (PCA), and cluster analysis was achieved successfully. Nine samples collected over 9 months period of each of the above fuels were collected and studied; the total number of all neat samples of fuels was 27 samples. The resulted PCA score model was used as a calibration model for detecting changes in gasoline composition. To imitate adulterated gasoline with diesel, kerosene gasoline was mixed with less expensive fuels, such as diesel and kerosene, with different volume fractions (5, 10, and 20 %). The same protocol used above for the classification has also been used successfully for the qualitative determination of 18 adulterated gasoline samples. The qualitative detection of diesel adulteration with kerosene of the same previous volumetric ratios was also achieved for nine adulterated diesel samples using the ¹H NMR and PCA.