The magnetisation and demagnetisation (where not demagnetised thermally) occur through intermediate states as shown (right). The magnetising and demagnetising wavelengths provide the energy for the system to reach the intermediate states which then relaxed non-radiatively to one of the two states (the intermediate state for magnetisation and demagnetisation are different and so the photon flux is not wasted by relaxation to the same state from which the system was just excited). A direct transition from the ground state to the magnetic state and, more importantly, vice versa is a forbidden transition, and this leads to the magnetised state being metastable and persisting for a long period at low temperatures.