Near-Field Signal Detection Using Sub-Wavelength Sized Planar Aperture Slider on Oxide Ferrite Media

Abstract

Optical transmission and surface characteristics of oxide ferrite (Fe3O4) as a write-once medium for near-field optical surface recording were investigated. Narrow line patterns were recorded on the surface of as-sputtered Fe3O4 (100 nm thick) using cw laser (532 nm) under various laser powers. Optical transmission intensities under far-field and near-field illumination methods were compared. Near-field signals exhibited signal transition width close to the aperture width, indicating high near-field readout resolution. However normalized transmission intensities were nearly the same, suggesting that signal characteristics depends on the recorded pattern not on the illumination method. No surface deformation were observed using atomic force microscope for low write power range (2.6–3.4 mW). Therefore, laser illumination of the medium surface probably causes a local oxidization of Fe3O4 to defect spinel ferrite (γFe2O3) resulting in a purely optical change without any surface deformation. Surface hardness and roughness were comparable with conventional hard disk surfaces.