Amorphous polyolefin substrate is very suitable for magneto-optical disk; it has small birefringence, small water absorption and good moldability. Because of these advantages, magneto-optical disks using amorphous polyolefin substrates have excellent reliability in read/write and mechanical characteristics.

In order to clarify the correlations between recording performances and fabrication processes in magneto-optical recording media, magnetic switching processes of TbFeCo films are studied. For a trilayer structure, with a thick magnetic layer, carrier to noise ratio(CNR) indicates maximum value for the composition with compensation temperature(Tcomp) being near room temperature. In a quadrilayer structure, on the other hand, where a thinner magnetic layer and Al reflector are employed, CNR indicates maximum vaiue for transition-metal(TM) rich composition with iower coercive force. Studies are made to interpret the results In terms of the difference in magnetic properties.

The 1 Miz dielectric constants of a variety of synthetic aluminate garnets: Y3Al5O12, Ho3A15O12, Y2.93Nd.07Sc2Al3O12 and Gd2.95Nd.05Sc1 98Cr .02A13O12 and several silicates: CaB2Si2O8 (danburite), Ca3Al2Si3O12 (grossular) and Mg2Al4Si5O18(cordierite) were determined using the two-terminal method with edge corrections. These data and polarizabilities derived from the published single crystal dielectric constants of simple oxides were used to compare compound polarizabilities obtained from the Clausius-Mosotti equation and the oxide additivity rule.

As a new dielectric layer for magneto-optical disks, we have developed AlGeN films prepared by the reactive sputtering method. The deposition rate, internal stress, and refractive index were investigated as functions of the sputtering parameters.AlGeN films were found to be superior in these points: high deposition rate, low internal stress (<1.5×109 dyne/cm2), and high refractive index (>2.4).

To evaluate dynamic characteristics and reliability, magneto-optical disks with TbFeCo double layer sandwiched by AlGeN layers were prepared on the polycarbonate substrate. Those disks had high carrier-to-noise ratio (C/N) even for 0.7 6 μm recording bit length. The acceleration test at a temperature of 60°C and a relative humidity of 90% was carried out. The defect error rate remained constant up to 2000 hours.

High reliability and good dynamic recording characteristics of the magneto-optical disk can be achieved by use of the AlGeN dielectric films.

Degradation of magneto-optic media by preferential oxidation of the rare-earth component, typically Tb. is a serious limitation to their lifetime and utility. In this paper, we present data on diffusion studies of 0 and TbFeCo through thin overlayers of a series of metals with differing electronegativities. Samples of TbFeCo were overcoated with Sm. Gd, Zr, Ni. or Pt, then vacuum transferred to an x-ray photoelectron spectrometer (XPS). Heating in situ was used to accelerate the diffusion process, and XPS to determine the extent of the diffusion. After 20 hours, the samples were depth profiled to further examine the effects of heating. The metals with the lowest electronegativities, Sm and Gd. provided the greatest resistance to Tb diffusion; however. it was noted that partial oxidation of these metals occurred during their deposition. These data suggest the use of thin rare-earth oxide diffusion barriers in connection with thick refractory overlayers for the protection of MO media.

The surface magneto-optic Kerr effect (SMOKE) has been used to explore the properties of ultrathin ferromagnetic films. The ultrathin regime corresponds to thicknesses less than the depth penetration of light and includes the monolayer range. The ultrathin regime possesses unique magneto-optic properties: the Kerr rotation and ellipticity, in general, behave differently than in the thick film limit. Measurements and simulation in the longitudinal geometry for bcc Fe on Au(100) provide a dramatic example of the metallic reflector enhancement effect due to the nonmagnetic Au underlayer. The rotation enhancement is accompanied by a high reflectivity, as opposed to being at the expense of the reflectivity. Measurements in both polar and longitudinal geometries for epitaxially-stabilized fcc Fe films grown on Cu(100) and Pd(100) indicate the presence of perpendicular surface anisotropy, which suggests new approaches to realizing vertical data-storage media.

The formation of oxides on rare earth/transition metal thin film alloys (FeTbCo and modifications thereof) has been explored by a combination of AES, XPS and RBS. The primary focus of these studies has been the interaction of H20 with the clean surface of the thin film alloys, and with pure iron and terbium thin films. Clear differences are observed between the chemisorption, product uptake profiles for H2O on Fe, Tb, and FeTbCo thin films and on FeTbCo thin films where a fourth metal (Pt) was incorporated into the alloy matrix.

Thin films of rare earlh transition metal (RETM) alloys are considered to be promising as media for high-density data storage in magneto-optic (MO) devices. These alloys, however, degrade rapidly through oxidation and corrosion due to the high reactivity of the RE metal. The addition of alloying elements could increase the intrinsic stability of the MO media [1,2]. Generally, two types of alloying elements have been considered: (1) an active metal (such as aluminum, titanium, chromium) or (2) a noble metal (such as platinum or gold). Although such alloying additions could improve the corrosion resistance, the exact mechanism of protection is not clearly understood. In this paper, we report the effects of Zr (active element) and Pt (noble element) on the oxidation behavior of FeTbCo MO films. Efforts were made to get a better understanding of the protection mechanisms provided by these two types of elements by using x-ray photoelectron spectroscopy (XPS).

The real long term aging phenomena at ambient temperatures, over 8 years, of amorphous TbFe thin films protected with a SiOx layer has been investigated, using Kerr magneto-optic effect. Our data indicate significant changes in the coercivity values for films with less than 500A thickness. In thicker films structure/stress relaxation effects appear to be significant. Studies of the stability of these films under accelerated aging are also presented.

In this paper, we would like to present a new polyolefin polymer, “Zeonex”, which has outstanding characteristics for optical uses.

As an optical disk substrate such properties as high clarity, low retardation, high heat resistance, and high humidity resistance properties are required. Glass can satisfy these requirements, but it is fragile and not suitable for mass production. PMMA has high clarity but has poor heat resistance and low humidity resistance. Polycarbonate, on the other hand, shows high heat resistance, but poor humidity resistance [1].

Nippon Zeon has developed a new polyolefin polymer, Zeonex, which clearly satisfies all of these requirements [2]. It has excellent features, especially:

1. a. low retardation: less than 20nm by Rotating Analyzer Ellipsometer

2. b. high heat resistance: Tg 140 °C by Differential Scanning Calorimeter

3. c. high humidity resistance: negligibly small linear expansion of disks in high humid conditions

4. d. low tilt of disk: less than 5 milli radian by Automatic Tilt Angle Tester

5. e. high transfer rate of patterns from stampers to disks

6. f. easy processing in injection molding

In the past eight years, the C/N value of Magneto-optic (MO) disks increased 5 db/per year and is now 60 db at 1 MHz. This advancement was achieved not only by the optical head improvement but also by the material design.

The C/N value depends on the several factors such as disk structure (on groove → on land, Trilayer → Quadrilayer), material (TC, θk, domain structure…).

In the present MO-disk, minimum bit length is 0.75 μm and track pitch is 1.6 μm. The bit density, thus obtained 8 × 10 bit/cm, is one order higher than the conventional magnetic hard disk. Data transfer rate of MO-disk, however, is 1 MB/s and is several times lower than that of hard disk.

In the coming 10 years, the bit density of MO-disk must be improved 10 times or more to the present density, as hard disks will realize in the past 10 years. Data transfer rate also must be improved from 1 MB/s or more than 3 MB/s in the near future.

These themes, however, seem possible to realize using following technologies: One is improvement of laser diode (λ = 800 → 600 →. 400 nm, multi-beam) and the other is improvement of MO material (large θk at shorter λ and lower TC).

From thus obtained results, we can estimate more than 20 times higher density and data rate in the coming 20 years.

Other important themes such as media life, high sensitivity, and overwrite technology are discussed.

The possibility of thermomagnetic bubble memory was investigated based on recent observations that domains can be written and erased simply by modulating the laser power without changing the bias field [1,2]. We focus our attention on writing with a rapidly pulsed laser beam. Writing process on TbFeCo films was observed real-time with a video camera mounted on a polarized optical microscope.

It was found that a thermomagnetically written domain may expand and shrink reversibly at a fixed bias magnetic field when laser pulses with various lengths are irradiated. When a spot on a film was irradiated with pulses with successively shorter time durations, the domain shrank and finally collapsed after the domain size became less than 0.2 μm. The domain size can be controlled reversibly by changing the pulse widths.

When a rapidly pulsed laser beam is scanned on the film, a cylindrical domain appears at the beam spot. When the beam spot is moved at a speed of about 1 μm/s, the domain follows the beam spot without any trace left behind. Small domains in the path are swallowed and disappear. However, when the path of the beam spot crosses a large domain, a stripe domain starts to be formed. The stripe shrinks when the scanning direction is reversed. When the stripe crosses another domain, the older domain has a tendency to be dragged to the direction of the scan. These phenomena are explained by assuming contraction of a cylindrical domain during the cooling process.

The problem of reflection of polarized light at any angle of incidence by multilayer magnetic and dielectric films is solved in specific cases by summation of reflected components, and in general by recursive application of the specific solutions. The Jones matrix convention is used to describe individual interfaces where the elements of the Jones matrix are the Fresnel coefficients for the reflecting (or transmitting) media. An explicit model, in terms of material parameters of individual films and film thicknesses, is presented for a system of n films, any of which can be magnetic or nonmagnetic. Also, limiting cases of zero magnetization and vanishing layer thicknesses are examined.