Photocontrol of magnetization in Al-substituted Fe3O4 thin films

Thin films of (111)-oriented spinel ferrite Al0.5Fe2.5O4 have been prepared by a pulsed-laser deposition (PLD) technique on α-Al2O3 (0001) substrates. The films exhibit cluster-glass behaviors with a spin-freezing temperature, Tg, near or above room temperature. The magnetization was found to increase following light irradiation below Tg, which indicates the photoinduced melting of cluster-glass states. An analysis comparing the dynamic behavior of magnetic response to light irradiation between zero-field-cooled (ZFC) states and field-cooled (FC) states at 10 K under various light intensities, I, revealed that the direct photoexcitation of spins occurs when I≤0.78 mW/mm2, while the thermal heating effect following the light absorption of the samples also contributes to the enhancement of magnetization when I≥1.22 mW/mm2. The magnetization of the films could be controlled by light irradiation even at room temperature. This suggests the possibility of utilizing these films in the development of novel magneto-optical memory devices.