EXCHANGE AND SPIN RELAXATION IN SOLID HE-3

Spin relaxation measurements in solid He-3 in the temperature region w here exchange dominates the behavior are reviewed and reanalyzed. A mo del which brings together the complex exchange modulation of the dipol ar interaction into a single correlation time is adopted. This may be regarded as introducing an effective pairwise exchange Hamiltonian. On the basis of this model new procedures are proposed for obtaining mat hematical expressions for the dipolar autocorrelation function and the spectral density functions, which determine the relaxation times. By the appropriate treatment of short-time and long-time asymptotic behav ior, together with a method for taking into account the mid-range beha vior, it is possible to fit the experimental data extremely well. The success of this procedure seems surprising in the light of multiple sp in exchange in solid He-3. It is an indication that the dominant excha nge processes scale with density in a similar way. This conclusion is supported by path-integral Monte Carlo calculations. Some consequences and implications of this conclusion are discussed. (C) 1997 American Institute of Physics.