Why an ac supply is not used to magnetize a bar of steel?

An AC supply is not used to magnetize a bar of steel because the alternating current continuously changes direction, causing the magnetic field to fluctuate. This results in the magnetization being ineffective, as the steel would not retain a stable magnetic orientation. For permanent magnetization, a direct current (DC) supply is preferred, as it creates a steady magnetic field that can align the domains in the steel and maintain the magnetization.