Evidence of exchange-coupled pairs relaxation in SrF2:Yb3+

Abstract

The angular and temperature dependences of the spin-lattice relaxation rate of the trigonal Yb3+ centres in a SrF2 single crystal have been investigated in the X band (9 GHz). In the temperature interval 2 to 12K, the experimental results can be fitted with the expression: T1-1=142.2(exp(12.5/T)-1)-1+0.197*109 exp(-111.67/T). At T>7.5K the relaxation of the Yb3+ ions is defined by an Orbach process (1961). For lower temperatures the experimental data are consistent with a cross-relaxation mechanism between the single Yb3+ ions and pairs of exchange-coupled Yb3+ ions, which turns out to relax by an Orbach process as well.