Introduction

The conventional media of magneto-optical data storage, the rare earth-transition metal alloys, are generally produced by radio frequency (rf) sputtering from an alloy target onto a plastic or glass substrate. For protection against the environment as well as for optical and thermal enhancement, the RE–TM alloy films are sandwiched between two dielectric layers (such as SiNx or AINx) and covered with a metallic reflecting and heat-sinking layer, before finally being coated with several microns of protective lacquer. The properties of the MO layer are determined not only by the composition of the alloy, but also by the sputtering environment and by the condition of the substrate's surface. The temperature at which the film grows, the sputtering gas pressure, the substrate bias voltage (self or applied), the rate of deposition, the surface roughness of the substrate, the quality of underlayer and overlayer can all affect the properties of the final product. It is therefore necessary to have accurate characterization tools with which to measure the various properties of the media and to establish their suitability for application as the media of erasable optical data storage.

The most widely used method of characterization for magnetic materials is vibrating sample magnetometry (VSM). With VSM it is possible to measure the component of net magnetization Ms along the direction of the applied field. For MO media, one obtains the hysteresis loop when the field is perpendicular to the plane of the sample.