You need lever release magnets. Flip the lever and the magnet holds, flip it the other way an it releases. We use them all the time at work. This version has 50lbs of lifting force, which would be way more than you need. But you get the idea. Machine shops and metal fabrication shop use them.
Mag-Mate B090 $116.41 Lifting Magnet, 50 Lb Cap, Trigger Release | Zoro.com