Two prevalent interactions in high-field solution magnetic resonance -radiation damping and the dipolar field - are shown to generate instability in spin systems with bulk magnetization. The instability is studied numerically by computing the largest Lyapunov exponent associated with the long-time spin dynamics, which is shown to be positive. An algorithm for investigating dynamical fluctuations in a spatiotemporally chaotic spin system is presented, and the finite-time largest Lyapunov exponents are calculated to gain insight into the growth rates of the system as a function of time. Numerical simulations and experimental results are compared to account for the appearance of experimental anomalies observed in multiple spin echo and pulsed gradient spin echo experiments.
The joint action of two readily observed effects in solution magnetic resonance-radiation damping and the dipolar field-are shown to generate spatiotemporal chaos in routine experiments. The extreme sensitivity of the chaotic spin dynamics to experimental conditions during the initial evolution period can be used to construct a spin amplifier to enhance sensitivity and contrast in magnetic resonance spectroscopy and imaging. Alternatively, amplification of intrinsic spin noise or tiny experimental perturbations such as temperature gradient fluctuations leads to signal interferences and highly irreproducible measurements. Controlling the underlying chaotic evolution provides the crucial link between amplifying weak signals and counteracting unwanted signal fluctuations.