The dissipation of toroidal magnetic fields and spin down evolution of young and strongly magnetized pulsars Gao, Zhifu Magnetars are a kind of pulsars powered mainly by superhigh magnetic fields. They are popular sources with many unsolved issues in themselves but are also linked to various high energy phenomena, such as quasi periodic oscillations (QPOs), giant flares, fast radio bursts, and superluminous supernovae. In this work, we first review our recent works on the dissipation of toroidal magnetic fields in magnetars and rotationally powered pulsars and then review the spin down evolution of young and strongly magnetized pulsars, especially of magnetars. Finally, we revisit the expression of braking index n, which is independent of the second derivative of spin frequency of a pulsar, and give some proposals for our future work.