SPIN-LATTICE RELAXATION OF CR-AL ACETYLACETONATE

The results of measurements of the spin-lattice relaxation properties of mixed single crystals of chromium and aluminium acetylacetonate are reported. Measurements were made at microwave frequencies (9·3 GHz) in the range of liquid helium temperatures. In dilute crystals, where the investigation was primarily concerned with the angular dependence of the relaxation time, satisfactory agreement with the single-ion theory was obtained by taking 2D = -1·18 cm-1. In concentrated crystals a reduction of spin-lattice relaxation time was observed together with a weaker temperature dependence. At the highest concentration (10 molar% Cr) the relaxation time was independent of temperature in the range 1·6-4·2°K. The results are interpreted in terms of a mechanism involving exchange-coupled pairs.