Co-59 NMR spectroscopy and relaxation in the metamagnetic system Y1-xGdxCo3

We studied the nuclear magnetic resonance (NMR) in intermetallic compounds of the series Y1-xGdxCo3. We found spectra exhibiting four lines, correspon ding to four magnetic sites of these compounds. However, the number of line s and their widths are strongly dependent on the radiofrequency (RF) power level, a fact that may help to explain some of the discrepancies found in t he NMR literature on these compounds. From the dependence of the NMR spectr a with the RF power we concluded that the site labeled 18h presents the lar gest local magnetic anisotropy. No significant changes are observed on the value of the hyperfine fields at each site as a function of the Gd concentr ation I, and that is explained in terms of the statistical distribution of Gd magnetic ions in the lattice. On the contrary, the spin-lattice and spin -spin relaxation rates, 1/T-1 and 1/T-2, measured at each line, are remarka bly dependent on the concentration. 1/T-2 exhibits a prominent peak at x si milar to 0.25, the concentration for which the Co ions undergo a magnetic p hase transition, whereas the same behavior is not observed in 1/T-1; this s uggests that the magnetic transition is followed by large longitudinal fluc tuations in the hyperfine held. (C) 2000 Elsevier Science B.V. All rights r eserved.