Driving an electromagnet through a shift register?
The absolute maximum current ratings are 500 mA, and generally one should not design a circuit to place components at absolute max conditions for very long (if at all; you might have one part on the extreme end of it's tolerance and all of a sudden you're exceeding maximums).

Reading deeper into the datasheet, it says the absolute maximum continuous drain current (all outputs on) is 150 mA, pulsed is 500 mA.  Peak drain current for a single output would be 500 mA.

It would be a better idea to use an external transistor and flyback diode to drive a moderate current device like your 0.5 A electromagnet.