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The dc magnetic susceptibilities of the orthorhombic DyF3 single crystals have been measured in the temperature range between 1.8 and 300 K. The susceptibility along the b-axis does not depend on temperature below TC = 2.55 K and is equal to the demagnetizing factor of the sample, that gives evidence for the ferromagnetic phase induced by the magnetic dipole–dipole interactions between the Dy3+ ions. The saturation moment of 8.5 μB/Dy3+ along the b-axis was determined from magnetization measurements. The observed strong anisotropy of the magnetic susceptibility at low temperatures agrees with the measured anisotropic g-tensor of the ground state of impurity Dy3+ ions in YF3 single crystals. The results of measurements are interpreted in the frameworks of the crystal field theory and the mean magnetic field approximation.

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The magnetic susceptibility of PrF 3 was measured in an external magnetic field of 0.01 T directed across and along the crystallographic c-axis at temperatures in the range 2-300 K. The maximum values of the measured susceptibilities (less than 1.2 × 10 −4 emu g −1 ) are consistent with the expected pattern of non-degenerate energy levels of the electronic 4f 2 configuration in the lowsymmetry crystal field. The longitudinal susceptibility decreases monotonically with the temperature increase while the transversal susceptibility has a broad maximum at 60 K. A crystal field analysis based on the magnetic susceptibility data and calculations in the framework of the exchange charge model was carried out. The set of crystal field parameters related to the crystallographic system of coordinates has been obtained and used to reproduce successfully the temperature dependences of the longitudinal and transversal components of the susceptibility tensor and the crystal field energies, as well as the parameters of the effective spin Hamiltonian of the 141 Pr nuclei.

Copper nuclear quadrupole resonance (NQR) and zero field nuclear magnetic resonance (ZFNMR) studies of YBa$_2$Cu$_3$O$_{6.5}$ show that a magnetic phase appears in underdoped 123 superconductors treated in ambient wet air. The studies give convincing evidence that the ``empty'' CuO chains play the role of easy water insertion channels. The reaction occurs first in ordered regions of the crystallites. The final product of the reaction is a non-superconducting antiferromagnetic compound characterized by at least two types of magnetically ordered copper ions with ZFNMR spectra respectively in the frequency ranges of 46-96 and 96-135 MHz respectively. Even for powder samples fixed in an epoxy resin, the reaction is found to occur partly after a few years.Comment: 3 pages, 3 figure

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.