Phenomenon of dynamical chaos in high-temperature spin systems of solids

We develop a theory that allows considering and describing the development of multiparticle correlations in paramagnetic spin systems. We show that in crystals with many equivalent nearest neighbors around a spin in a lattice, an infinite system {(}of size $\sim10^{23})$ of coupled differential equations for time correlation functions describing multiparticle correlations is reducible to the diffusion equation with an imaginary diffusion coefficient. The equation can be solved analytically in the lowest-order approximation of the theory. The equation obtained in the next approximation must be solved numerically because a discontinuity of the diffusion coefficient appears. The obtained results agree well with experimental data. The observed mutual similarity of the calculated time correlation functions and several other characteristic features appearing in the spin system dynamics are consequences of the development of dynamical chaos.