The photomagnetic effect is the effect in which a material
acquires (and in some cases loses) its ferromagnetic properties
in response to light. The current model for this phenomenon is a
light induced electron transfer, accompanied by the reversal of
the spin direction of an electron. This leads to an increase in
spin concentration, causing the magnetic transition. Currently
the effect is only observed to persist (for any significant
time) at very low temperature. But at temperatures such at 5K,
the effect may persist for several days. . The photomagnetic
effect is found to be repeatable i.e. the material can be
magnetised, then demagnetised (either by applying the relevant
wavelength or by heating above the critical temperature) then
remagnetised without any measurable change between cycles   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