Magnetically induced super resolution (MSR) is used to read “below-diffraction-limit” recording marks on magneto-optical (MO) media. A nanosecond-order laser pulse irradiated onto MO media can create a quasi-circular temperature profile, thereby yielding a quasi-circular sub-µ m aperture to effectively derive a readout signal from sub-µ m marks recorded on the disks. In this study, the pulsed irradiation and conventional DC readout methods are applied to a MO disk with a center aperture detection (CAD) structure to quantitatively evaluate their readout performance. The size and shape of the effective aperture, jitters due to readout parameters, and aperture wall width generated are studied. The feasibility of the pulsed irradiation readout is then assessed.
The required bias field of a sperimagnetic film is governed by a finite exchange coupling coefficient (λ) mainly determined by the subnetwork coupling. From the study of a series of (Dy,Tb)FeCo films at compensation composition, it is found that λ is mainly determined by the concentration of the rare earth components. Moreover, the exchange integral between rare earth and transition metal subnetworks can be derived from λ so that the number of uncertain parameters for mean field modeling is reduced. Accordingly, the bias field required for magneto-optical recording is mainly proportional to λ that can be obtained quantitatively from either measurement and/or mean field modeling.
Exchange-coupled double-layered (ECDL) films were adopted to increase density of magnetically induced super-resolution (MSR) media by using center aperture detection scheme, and to improve sensitivity of switching field simultaneously. A carrier to noise ratio of 40 dB was obtained at 0.5 µ m recording marks produced by a switching field of 75 Oe. Temperature dependence of interface wall energy affects recording/playback characteristics of ECDL MSR disks considerably.
Anisotropy dispersion of rare earth constituents, and canting between rare earth and transition metal subnetworks were used to explain the recording characteristics of (Dy,Tb)FeCo magneto-optical recording films. Through the quantitative measurements and mean field calculations of the exchange coupling coefficient ').", we have found that the higher A is, the higher required bias field will be during recording. Therefore, the recording characteristics of ferrimagnetic and sperimagnetic films can be determined and further improved through careful characterization of A of magneto-optical media.
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