Spectral-Density Function in the System of Randomly Distributed Spins with R^<-n> Interactions

概要

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An approximate method dealing with the spectral-density function in the system of randomly distributed spins is presented, assuming a general interaction with distance dependence of R^<-n>. This method allows us to cover the whole range of concentration and accordingly to interpolate two existing theories valid separately for the high and low concentrations of impurity spins. For the system with R^<-3>-interaction, the present result is compared with previous theoretical ones as well as the observed EPR width of dilute chromium ions in ruby, in reasonable agreement. The result for the system with R^<-5>-interaction is compared with recent experiments on the longitudinal nuclear spin relaxation time in solid H_2 and D_2. It is pointed out that the usual result based on the Gaussian approximation breaks down at the higher concentration for the system with shorter-ranged interaction. A detailed study of the correlation effect on the spectral density at zero-frequency is given for the system with R^<-5>-interaction, in an excellent agreement with the experiments.
理論物理学刊行会の論文
1972-12-25