Parametrical Instability in Nuclear Spin Systems with Dipole-Dipole Interactions
It is shown that when the values of the radiofrequency magnetic field amplitude are more than the critical value, quasi-thermodynamical description of the dynamics of a nuclear spin system with dipole-dipole interaction is impossible because of the unlimited growth of a number of parametrically excited magnons. The critical values of the radiofrequency field and the energies of the first excited magnons are calculated. It is important that in contrast to electron spin systems, in nuclear spin systems the probability of excitation of resonant parametric magnons vanishes if detuning is equal to zero, but the magnons from the top or bottom of the spectrum zone are excited. It is mentioned that such an instability can be a reason for NMR chaos. Copyright 1998 Academic Press. Copyright 1998 Academic Press