CHARACTERIZATION OF MAGNETO-OPTICAL RECORDING MEDIA

Roger  A. HAJJAR

This dissertation discusses the optical, magnetic and transport properties of magneto‑optical recording media. The various custom‑made and off‑the‑shelf instrumentation used in this study include : a Vibrating Sample Magnetometer (VSM), a modified polarization microscope, a polar Kerr effect loop tracer, a variable angle of incidence ellipsometer and magnetoresistance/ Hall effect/ resistivity probes. Most of the samples studied were analyzed for determination of their composition and thickness by Rutherford Back Scattering (RPS) and X‑Ray Fluorescence (XRF). The samples investigated were manufactured in several industrial and academic laboratories under different deposition conditions.

The optical properties measured include Kerr rotation angle and ellipticity, Fresnel reflectivity coefficients, and calculation of the dielectric tensor. The magnetic properties include measurements of saturation magnetization, coercivity, anisotropy field, calculations of exchange energy parameters, domain wall, and anisotropy energy densities from experimental observations. The transport properties include measurements of magnetoresistance and Hall effect with three different geometries and calculation of the resistivity tensor.

The modeling work consisted of modeling the optical path for various instruments, the current distribution in magnetic films, and the calculation of the demagnetizing energy using the fast Fourier transform technique.

This dissertation concludes four years of investigation of the properties of MO media. Further research should involve examining the magnetic nanostructure of these films in order to define the limits on the data density of this media. This work should address fundamental issues such as the size of the smallest thermomagnetically written domain and the shape and regularity of the domain. This issue spurred our involvment in the Magnetic Force Microscope (MFM) which has been constructed during the past year by H. Sukeda and myself in an effort to observe magnetic domains in greater detail and to study the stability of the domains by moving a highly magnetized needle near the sample (Sukeda et al, 1991).

On another front, investigations should be made into increasing the signal to noise by engineering better media with a larger Kerr rotation at shorter wavelengths and eliminating other sources of noise such as the predominant laser noise. Furthermore, integrated heads with shorter wavelengths and multiple beams will greatly enhance the performance of MO drives.