Suppose I have a superconducting solenoid MRI magnet (cooled with liquid helium) producing a static magnetic field around it. I approach the magnet bore with a steel rod in my hand. The rod starts to pull towards the magnet and i have to work against the pull in order not to let it attach onto the machine. Now my question is, have I reduced the energy of the static magnetic field when Ive pulled the rod away from the magnet or is there some sort of compensatory mechanism that keeps the static field fixed to its nominal value? I know that the pull is largely due to the spatial gradient of the magnetic field but what or who is doing the work on the rod?