  A theoretical study of dynamics of small thermal and electromagnetic
perturbations in type-II superconductors in the flux creep regime with a
nonlinear current-voltage characteristics is performed. For this purpose, the
space-time evolution of temperature and electric field was calculated using the
heat diffusion equation, coupled with Maxwell's equations and material law,
assuming that the applied magnetic field is directed parallel to the surface of
the sample. A threshold field $B_j$ for the occurrence of thermomagnetic
instability has been found assuming that the heat flux diffusion is
considerable faster than the magnetic flux diffusion in superconductor. The
obtained stability criterion for the thermomagnetic flux jumps demonstrates the
extremely high sensitivity of the threshold field on the values of the critical
current density and external magnetic field sweep rate.
