We report Cd nuclear magnetic resonance (NMR) and Re nuclear quadrupole resonance (NQR) studies on Cd(2)Re(2)O(7), the first superconductor among pyrochlore oxides (T(c) approximately 1 K). The Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below T(c) exhibits a pronounced coherence peak and follows the weak-coupling BCS theory with nearly isotropic energy gap. The results of Cd NMR point to a moderate ferromagnetic enhancement at high temperatures followed by a rapid decrease of the density of states below the structural transition temperature of 200 K.

We report, for magnetic fields of 0, 8.8, and 14.8 T, measurements of the temperature dependent 63 Cu NMR spin lattice relaxation rate for near optimally doped YBa 2 Cu 3 O 72d , near and above T c . In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required precision and implications of the experiment regarding issues including the spin gap or pseudogap. [S0031-9007(98)08138-1] PACS numbers: 74.25.Nf, 74.72.Bk, 76.60.EsA dominant feature of optimally and underdoped cuprates is the appearance of a pseudogap in the normal state excitation spectrum. The microscopic mechanism which is responsible remains a mystery. A number of scenarios for explaining the pseudogap have been proposed (see Ref.[1] for a recent review). However, no calculations of the consequences of a large applied field for the pseudogap have been published. The high magnetic field behavior of the pseudogap provides additional experimental characterization of the pseudogap which is crucial for differentiating between various pictures.We report very high accuracy measurements of the magnetic field dependence of the 63 Cu spin lattice relaxation rate in near optimally doped YBa 2 Cu 3 O 72d . Our measurements demonstrate, in sharp contrast with previous work [2-6], that there is no magnetic field dependence to 63 ͑T 1 T͒ 21 in YBa 2 Cu 3 O 72d . This result has three important ramifications. Although the magnetic fields we apply shift T c down by as much as 8 K, the onset of pseudogap effects does not shift down in temperature. Hence the pseudogap is unrelated to superconducting fluctuations, even in near optimally doped YBa 2 Cu 3 O 72d where the gap behavior appears just above T c . The onset of the pseudogap is very rapid, clearly demonstrating that its magnitude is temperature dependent, opening very rapidly near 110 K. Finally, the absence of any field effect indicates a relatively large energy scale for the gap mechanism. If dynamical pairing correlations or preformed pairs are involved, the length scales must be very short.The 63 Cu NMR spin lattice relaxation rate reveals the spin part of pseudogap behavior, the "spin gap." In underdoped YBa 2 Cu 3 O 6.6 , 63 ͑T 1 T͒ 21 famously exhibits a broad maximum in the vicinity of room temperature and then decreases as T approaches T c from above. In optimally doped YBa 2 Cu 3 O 72d (data shown in Fig.

We report the results of Cu and Cl nuclear magnetic resonance experiments and thermal expansion measurements in magnetic fields in the coupled dimer spin system TlCuCl3. We found that the field-induced antiferromagnetic transition as confirmed by the splitting of NMR lines is slightly discontinuous. The abrupt change of the electric field gradient at the Cl sites, as well as the sizable change of the lattice constants, across the phase boundary indicate that the magnetic order is accompanied by simultaneous lattice deformation.

A complex study of magnetic properties including dc magnetization, 1 H NMR, and magnetic torque measurements has been performed for the organic conductor κ-(BETS) 2 Mn[N(CN) 2 ] 3 which undergoes a metal-insulator transition at T MI ≈ 25K. NMR and the magnetization data indicate a transition in the manganese subsystem from paramagnetic to a frozen state at T MI , which is, however, not a simple Néel type order. Further, a magnetic field induced transition resembling a spin flop has been detected in the torque measurements at temperatures below T MI . This transition is most likely related to the spins of π electrons localized on the organic molecules BETS and coupled with the manganese 3d spins via exchange interaction.