Orientational dependencies of dynamics and relaxation of multiple quantum NMR coherences in one-dimensional systems

Dissipative dynamics of multiple-quantum NMR coherences in two-spin systems

Multiple-quantum (MQ) NMR experiments were performed at a special orientation of a hambergite (Be2BO3OH) single crystal, which consists of alternating zigzag proton chains. At the chosen orientation, one of the dipolar coupling constants in the chain becomes zero and the system becomes a set of well-isolated dipolar coupled spin pairs. The relaxation of the spin pairs in the MQ NMR experiment was studied on the basis of the Lindblad equation. Fermi's golden rule was used to investigate the relaxation mechanism. The agreement of the calculated relaxation time with the experimental value (125 μs) suggests that the dipole-dipole interactions with protons surrounding the pair are responsible for the relaxation of MQ coherences.

1H multiple quantum NMR in alternating quasi-one-dimensional spin chains of hambergite

Multiple quantum (MQ) dynamics was investigated in quasi-one-dimensional ¹H zigzag spin chains in hambergite (Be₂BO₃OH) single crystals. Due to the non-linear arrangement of the spins, dipolar coupling strengths alternate along the chain. To solve the problem of MQ NMR experiments taking too much time due to extremely long ¹H spin-lattice relaxation times, the samples were exposed to gamma irradiation to produce the defects accelerating the relaxation. The influence of the radiation dose was investigated. The experimental dependencies of MQ coherence intensities on the MQ excitation time in alternating spin chains were obtained and compared with the theory for inhomogeneous spin chains with nearest neighbor interactions developed earlier. The correspondence of the observed MQ dynamics to the alternating spin chain was demonstrated.

1H NMR in a quasi-one-dimensional zig-zag spin chain of hambergite, Be2BO3(OH)

One-dimensional spin chains are important testbeds for the investigation of quantum many-body systems. Here, we introduce a new quasi-one-dimensional chain of spin-1/2 ¹H nuclei in hambergite (Be₂BO₃(OH)) crystal. The distinctive feature of hambergite is the zig-zag arrangement of the spins in the chains compared to the systems reported earlier. A single crystal of hambergite was investigated experimentally using ¹H nuclear magnetic resonance at different orientations in the external magnetic field. The experimental spectra were compared with the Van Vleck's second moments calculated from the structural data. For the orientation of the chain along the external magnetic field the resonance resembles that of the linear spin chains and the calculated contributions to the second moment from spins within one chain of hambergite amount to 96%. For other orientations the spectra demonstrate features specific to the zig-zag chain. Our results show that ¹H nuclei in hambergite crystals could serve a good model of a well-isolated zig-zag spin chain.