Radio pulsars as progenitors of AXPs and SGRs: magnetic field evolution   through pulsar glitches
  Glitches are common phenomena in pulsars. After each glitch, there is usually a permanent increase in the pulsar's spin-down rate. Therefore a pulsar's present spin-down rate may be much higher than its initial value. Thus the characteristic age of a pulsar based on its present spin-down rate and period may be shorter than a pulsar's age. At the same time, the permanent increase of its spin-down rate implies that the pulsar's surface magnetic field is increased after each glitch. Consequently after many glitches some radio pulsars may evolve into AXPs and SGRs, i.e., strongly magnetized and slowly rotating neutron stars. 
J. R. Lin and S. N. Zhang