Photo-enhanced magnetization in Fe-doped ZnO nanowires

An emerging branch of electronics, the optospintronics, would be highly boosted if the control of magnetic order by light is implemented in magnetic semiconductors' nanostructures being compatible with the actual technology. Here, we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to temperatures slightly below room temperature. This enhancement is related to the existence of an oxygen vacancy V_O in the neighborhood of an antiferromagnetic superexchange Fe³⁺-Fe³⁺ pair. Under illumination, the V_O is ionized to $V O +$ giving an electron to a close Fe³⁺ ion from the antiferromagnetic pair. This light excited electron transition allows the transition of Fe³⁺ to Fe²⁺ forming stable ferromagnetic double exchange pairs, increasing the total magnetization. The results presented here indicate an efficient way to influence the magnetic properties of ZnO based nanostructures by light illumination at high temperatures.