Spin dynamics in LiCu$_2$O$_2$ and NaCu$_{2}$O$_{2}$ low-dimensional helical magnets

Comprehensive NMR investigation of low-frequency spin dynamics of LiCu$_2$O$_2$ (LCO) and NaCu$_{2}$O$_{2}$ (NCO) low-dimensional helical magnets in the paramagnetic state has been carried out for the first time. Temperature dependences of the spin-lattice relaxation rate and anisotropy on various LCO/NCO nuclei have been determined at various orientations of single crystals in an external magnetic field. The spatial asymmetry of spin fluctuations in LCO multiferroic has been discovered. The quantitative analysis of the anisotropy of spin-lattice relaxation in LCO/NCO has allowed estimating the contributions of individual neighboring Cu$^{2+}$ ions to the transferred hyperfine field on Li$^{+}$(Na$^{+}$) ions.