Johannes Hendrikus Maria Spruit

Scanning magnetic force microscopy on Co/Pt magneto‐optical disks

High resolution images of domains written on Co/Pt magneto‐optical disks were obtained using scanning magnetic force microscopy. The key advantage of this technique compared to electron microscopy techniques is that regular disks can be used. We studied the influence of the multilayer composition and preparation conditions as well as the effect of the pregrooves and the incorporation of a Pt underlayer, on the structure of the domains on the disk. Marks were written both with laser and magnetic field modulation, and carrier and noise levels were determined. Regularly shaped and subdomain‐free marks for both writing schemes were obtained for multilayers with about 4‐A‐thick Co layers and Pt layers thinner than 15 A. The magnitude of the coercive field had only a minor influence on the domain structure. On the other hand, the preparation conditions and the structure of the base layers have a large impact on the recording conditions and domain structures.

Performance of Modulation Codes in Various Optical Recording Media

The performance of modulation codes has been measured in ablative and magneto-optic recording media as well as in mastered direct discs. The modulation codes studied include NRZ (i.e. the uncoded bit stream), runlength limited sequences, multi-level recording schemes, and differentially detectable codes. We also studied the performance of codes when the optical channel is equalised, particularly the case of partial response detection of NRZ. The general conclusions are that: 1) differentially detectable codes require the full penalty in data density caused by the loss in code rate, 2) multi-level recording does not offer significant advantages, and step-constrained multi-level codes perform worse than their unconstrained counterparts, 3) runlength limited sequences are useful codes to enhance the density while offering additional practical advantages, and 4) partial response detection of uncoded bit streams transmitted through an equalised optical recording channel achieves the highest density.

Co/Pt and Co/Pd multilayers as new magneto‐optical recording media (abstract)

In this paper we will discuss Co/Pt and, to a lesser extent, Co/Pd multilayers optimized for magneto‐optical storage applications. Perpendicular magnetic anisotropy and square hysteresis loops are achieved for multilayers with a total thickness below about 200 A if they consist of very thin (≂4 A) Co layers alternated with 10–20‐A Pt layers. Multilayer made by evaporation show a high coercivity (≳100 kA/m) and have proven to be suitable as magneto‐optical recording medium. Recently we showed that Co/Pt layers with high coercivity can be made by sputtering as well, if not Ar but Kr is used as sputter gas.1 We will discuss the properties of Co/Pt multilayers in relation to the preparation technique and will present magneto‐optical recording results for both evaporated and sputtered Co/Pt multilayer films. The written domain patterns can be very regular, as observed by scanning magnetic force microscopy, and a CNR as high as 55 dB (1 MHz carrier, 5 m/s, 30 kHz BW) is observed. The good oxidation and corrosio...