Cu2+ spin-lattice relaxation in zinc tungstenate

The rate of spin-lattice relaxation (SLR) of Cu2+ ions at the frequency of 9.8 GHz in the temperature range of 0.08-4 K in zinc tungstate monocrystals, is measured. It is established that exponential temperature dependence of SLR rate and transition to W approximately cthhv/2kT are the consequence of the effect of foreign impurities on the relaxation of Cu2+ ions (e. g. Ni2+, Fe3+). Even at the lowest Cu2+ ion concentrations signs of the Kronig-Van Vleck mechanism are absent. The dominating role at the lowest concentrations is played by concentration depending mechanism with the W approximately T2 temperature dependence