SOME PECULIARITIES OF SPIN-LATTICE RELAXATION OF IMPURITY RARE-EARTH IONS IN CRYSTALS, CAUSED BY THE STRUCTURE DEFECTS

The spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum ga rnets (YAG) and for Yb3+ ions in CaF2, in the low-temperature range ha ve been measured. For the first system the temperature dependence of t he relaxation rate is determined to a great extent by the method of sa mple preparation. For samples grown by the method of the horizontally oriented crystallization the dependence is described as T-l(-1) = AT(n ), n congruent to 4.7, which is an evidence of an influence of local s tructure disordering on the relaxation. The temperature dependence of the relaxation rate in CaF2:Yb is also ''anomalous'': T-l(-1) = AT(3.3 ). The results are compared with the previous data on the relaxation i n similar systems, and with other cases of observation of ''anomalous' ' temperature dependences. Different manifestations of the local cryst al defects in spin-lattice relaxation are discussed.