Pierre Borckmans

Irreversibility in paramagnetic spin systems: I. Kinetic equations for the two-spin autocorrelation functions in the high field, high temperature approximation

Abstract In a recent paper P. Resibois and M. De Leener derived kinetic equations for the spin autocorrelation function in the case of a Heisenberg spin system in the high temperature and the Weiss limit. Following the same method, i.e. starting from the von Neumann equation for the spin density matrix and reorganizing the perturbation expansion of the spin autocorrelation functions, we derive similar kinetic equations in the case of paramagnetism in the high field, high temperature approximation. These equations are non-markovian and highly nonlinear.

SPIN AND INTERSPIN ENERGY DIFFUSION COEFFICIENTS

Abstract Values of the spin and interspin energy diffusion coefficients for CaF 2 and bcc solid 3 He are presented. They are evaluated from the general diffusion equations derived previously by the authors.

Spin echoes and negative time evolution in paramagnetic spin systems

The positive and negative time evolution of a paramagnetic spin system after two phase-shifted radio-frequency pulses is studied in the frame of the general theory of non-equilibrium statistical mechanics. The evolution of non-equilibrium correlations is described and information about the initial conditions which may give rise to this type of evolution is obtained. The results are in good agreement with experimental data, e.g., from the “solid echo” and from Jeener and Broekaets double-pulse experiments.