  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$_{\rm O}$ in the neighbouring of an
antiferromagnetic superexchange Fe$^{3+}$-Fe$^{3+}$ pair. Under illumination
the V$_{\rm O}$ is ionized to V$_{\rm O}^+$ giving an electron to a close
Fe$^{3+}$ ion from the antiferromagnetic pair. This light excited electron
transition allows the transition of Fe$^{3+}$ to Fe$^{2+}$ forming stable
ferromagnetic double exchange pairs, increasing the total magnetization. The
results here presented indicate an efficient way to influence the magnetic
properties of ZnO based nanostructures by light illumination at high
temperatures.
