Cation-deficient spinel ferrites: Application for high-density write-once optical recording

Thin films of defect spinel ferrites can be used as write-once read many me dia working with blue wavelengths. In fact, because these non-stoichiometri c ferrites are metastable, they can be transformed into corundum phases at moderate temperatures by a laser spot. The transformed regions have differe nt optical indices from the starting ferrite film, making the readout proce ss possible. Recording density of about 5 bits/mu m(2) was demonstrated.