Spin dynamics and susceptibility approaching the NM-M transition in K_xKCl_1-x

We report ESR measurements of K_xKCl_1-x melts at 800 degrees C which for the first time have been studied over a wide composition range approaching the nonmetal-metal transition (10^-4<or=x<or=10^-1). The concentration has been varied precisely by in situ Coulometric titration. The observed motional linewidth narrowing gives evidence that fast electronic exchange processes prevail in the nonmetallic melts. The spin susceptibility exhibits strong deviations from a simple Curie limit and its magnitude strongly indicates that only a small fraction of excess electrons exists in paramagnetic states. Both the spin dynamics and the spin susceptibility show clear changes near x=0.05 indicative of the onset of a Mott-Anderson transition. Over the whole nonmetallic regime the ratio of spin susceptibility and electronic conductivity is found to be constant.