We have carried out 63,65 Cu NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular lattice antiferromagnet CuCrO 2 . The measure ments were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conver sion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.

Systematic measurements of the 63 Cu(2) NQR line width were performed in underdoped YBa2Cu3O7−y samples over the temperature range 4.2 K < T < 300 K. It was shown that the copper NQR line width monotonically increases upon lowering temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed dependence is explained by the fact that the energy of a condensate of sliding charge-current states of the chargedensity-wave type depends on the phase of order parameter. Calculations show that this dependence appears only at T < Tc. Quantitative estimates of the line broadening at T < Tc agree with the measurement results.

7 Li NMR spectra were measured in a magnetic field up to 17 T at temperatures 5-30 K on single crystalline LiCu2O2. Earlier reported anomalies on magnetization curves correspond to magnetic field values where we observe changes of the NMR spectral shape. For the interpretation of the field and temperature evolutions of our NMR spectra, the magnetic structures were analyzed in the frame of the phenomenological theoretical approach of the Dzyaloshinskii-Landau theory. A set of possible planar and collinear structures was obtained. Most of these structures have an unusual configuration; they are characterized by a two-component order parameter and their magnetic moments vary harmonically not only in direction, but also in size. From the modeling of the observed spectra, a possible scenario of magnetic structure transformations is obtained.

Two maxima in transverse relaxation rate of Cu(2) nuclei in YBa2Cu3O7−y are observed, at T =35 K and T = 47 K. Comparison of the 63 Cu(2) and 65 Cu(2) rates at T = 47 K indicates the magnetic character of relaxation. The enhancement at T = 47 K of fluctuating local magnetic fields perpendicular to the CuO2 planes is connected with the critical fluctuations of orbital currents. Maximum at T = 35 K is connected with the appearance of inhomogeneous supeconducting phase. Together with data published to date, our experimental results allow to suggest a qualitatively new phase diagram of the superconducting phase.

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