The Strong Magnetic Field Decay and Evolution of Radio Pulsars on the   P--\.{P} Diagram
  In this work we have analysed various data on radio pulsars and we have shown that magnetic field decay of a factor about 10-20 is necessary to explain their evolution, in particular to remove the discrepancy between the characteristic and the real ages. The character of the field decay is exponential with a characteristic time of about 3$\times10^6$ yr. Observational data on single X-ray pulsars which radiate due to cooling also support this result. 
O. H. Guseinov, A. Ankay, S. O. Tagieva