I have never heard of such thing. But it would really suit my needs.
I'm inventing a device and during it's operation, it should be able to catch an iron object any time (with a permanent magnet). The device should be mobile, so using inductor would really reduce the time of operation.
But the device must also be able to turn the field off, so that the objects can drop down.
I only could think of one concept: Put inductor behind a permanent magnet in a way that when the inductor is turned on, it's field will negate the permanent field of the magnet.
As you see it's my attempt to draw a coil connected to permanent magnet (isolator is in-between). When the coil goes on, it should produce field of oposite direction to the field created by magnet.
Is this possible? Is there a better trick?