Magnetism, structure, and superconductivity of Cd2Re2O7 pyrochlore:: Cd and ReNMR

We present Cd and Re NMR results on Cd2Re2O7, the first and as yet the only superconductor (T-c similar or equal to 1 K) among pyrochlore oxides. Re spin-lattice relaxation rate below T-c exhibits a pronounced coherence peak and follows the weak-coupling BCS with nearly isotropic energy gap. Cd NMR points to moderate ferromagnetic enhancement at high temperatures followed by rapid decrease of the density of states below 200 K, and to strong suppression of spin fluctuations below similar to75 K. Cd and Re NMR spectra reveal two structural phase transitions, one at 200 K and another at 120 K. Re NQR rules out any magnetic or charge order. (C) 2003 Elsevier Science B.V. All rights reserved.