Why does a piece of iron in a current-carrying loop increase the magnetic field strength? The iron is a permanent magnet and adds to the field of the current-carrying loop. The electromagnetic field of the current-carrying loop is amplified because it aligns the domains in the iron. The iron acts as a capacitor and stores spinning electrons, thus increasing the magnetic field. The presence of the iron decreases the resistance in the current-carrying loop, thereby allowing more current to flow