B and P evolution in the recycling process. The upper left panel shows the joint evolution of B and P. The upper right and lower left panels are their evolution as a function of accreted mass ΔM. The solid, dashed, and dotted lines are the evolutionary tracks with the accretion rate of 10¹⁸ g/s, 10¹⁷ g/s, and 10¹⁶ g/s, respectively. The initial B and P are taken as B₀ = 5 × 10¹² G and P₀ = 1 s. The lower right panel is a zoom-in view of the lower left panel in a linear scale for spin periods shorter than 5 ms.