PROTON SPIN-LATTICE RELAXATION-TIMES IN YTTERBIUM HYDRIDES

The measurements of the proton (NMR) spin-lattice relaxation times hav e been made in a series of ytterbium hydrides, YbH(x). Results are rep orted for x=1.80, 1.95, 2.00 and 2.62 and temperatures 4.2 less-than-o r-equal-to T less-than-or-equal-to 297 K. In the orthorhombic phase (1 .80 less-than-or-equal-to x less-than-or-equal-to 2.00), the spin-latt ice relaxation times are dominated by the hyperfine interaction of pro tons with conduction electrons and the spin diffusion mechanism. In th e cubic phase (x = 2.62), the relaxation times are five orders of magn itude shorter than in the orthorhombic one. This is interpreted in ter ms of the proton coupling with the Yb3+ ion spin fluctuations.