Mutual annihilation between neighboring fluxoids of opposite flux direction is proposed as an origin for some instabilities in hard superconductors. The presence of a reversal of the direction of magnetic induction within the superconductor is recognized as a necessary condition for the annihilation instability, and the boundaries of the region of instability can be calculated from critical-state concepts. Specimens of coldworked niobium-zirconium alloys were found to display a region of instabilities with boundaries and characteristics expected of the annihilation instability.

• Received 4 September 1964

DOI:https://doi.org/10.1103/PhysRev.137.A1205