lets say i got by a chance a bunch of atoms, when which happens to have 50% up and 50% down spins when i activate a magnetic field. now, some of the down (the excited ones) would decay into an up state and emmit a photon. where does the energy for light came from? the bunch of atoms didnt have potential energy untill i brought the magnet, and i dont think it will be physically harder to push a magnet under the sample as a function of number of atoms in it (more atoms emmit more light)... does it because they cancel the magnetic field and reduce its intensity? i can take the magnet back and the magnetic field would get to its normal strength... will it be harder for me to take the magnet away from the sample as a function of number of atoms in the sample? will the magnet itself lose its magnetism?