Kinetic equations are presented for single-particle spin-density matrices with consideration for Heisenberg exchange interaction in bimolecular collisions of particles and dipole—dipole spin—spin interaction between particles. It is shown that interactions between individual paramagnetic particles albeit rather weak compared to exchange interaction may result in a nonequivalent spin exchange. Spin-coherence transfer generates collective modes of quantum spin coherence motion. Collective-resonance lines feature a mixed form (absorption + dispersion). A new interpretation of the exchange narrowing of spectrum in case the rate of spin-coherence transfer is sufficiently large is proposed. An advanced theory of paramagnetic relaxation of paramagnetic particles in dilute solutions due to dipole—dipole interaction is discussed. A modern paradigm of spin exchange is also presented.

Keywords: spin probes, exchange and dipole—ldipole interaction, spin-exchange rate constant, decoherence of spins, spin coherence transfer, EPR spectrum shape, mixed form of spectral lines (absorption + dispersion), exchange narrowing of spectra PACS: 75.50.Mm, 75.78.−n, 76.30.−v (all) DOI: 10.3367/UFNe.2018.08.038421 URL: https://ufn.ru/en/articles/2019/10/a/ 000508386600001 2-s2.0-85069628365 2019PhyU...62..951S Citation: Salikhov K M "Current state of the spin exchange theory in dilute solutions of paramagnetic particles. New paradigm of spin exchange and its manifestations in EPR spectroscopy" Phys. Usp. 62 951–975 (2019) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Received: 28th, June 2018, revised: 17th, August 2018, accepted: 31st, August 2018 Оригинал: Салихов К М «Состояние теории спинового обмена в разбавленных растворах парамагнитных частиц. Новая парадигма спинового обмена и его проявлений в ЭПР-спектроскопии» УФН 189 1017–1043 (2019); DOI: 10.3367/UFNr.2018.08.038421