Abstract
Non-stoichiometric spinel ferrite films are proposed in this work as write-once recording layers for high density optical storage with blue laser sources. Two types of ferrite films has been studied: mixed Co-Cu ferrites and γ-Fe2O3 which are anionic deficient and cationic deficient phases respectively. For Co-Cu ferrites films, the minimal writing powers leading to “readable” bits were 15 and 4 mW for red and blue laser spots respectively. Writing is realized by local oxidation of the film by laser heating. The readout signal takes benefit of the resulting changes in optical properties and bump formation on media surface.γ-Fe2O3 films can be locally transformed into α-Fe2O3 by blue spot irradiation without any topographical modification of the film surface. The transformed domains can be optically read because of different optical indices for γ and α phases in the blue spectral region. Writing sensitivity of γ-Fe2O3 film can be improved by adding 10 nm thick absorptive Ti layer. 5 mW is then enough to write bits at 488 nm. For this type of structure, small bumps are however formed on the written domains.
