Yumi Mizusawa

Observation of thermomagnetically written domains by Lorentz electron microscopy in Tb‐Co and Tb‐Fe‐Co disks

For better understanding of the read/write properties of magneto‐optical disks, thermomagnetically written domains were observed by Lorentz electron microscopy. The domains were written in the quadrilayered medium with 25‐nm‐thick Tb‐Co film and in the trilayered medium with 50‐nm‐thick Tb‐Fe‐Co film, which were sputtered on pregrooved resinous substrates. Recording power and frequency were varied at intervals of 3.5 mm in a radial direction of the disk, and each recording position was observed individually. Qualitative understanding of the read/write properties, such as carrier‐to‐noise ratio (C/N) and jitter, were well achieved from Lorentz images of the domains. It is found that the C/N value of the Tb‐Fe‐Co film with a higher figure of merit (Rθk ) is lower than that of the Tb‐Co film with a lower value of Rθk . The reason for this is believed to be due to a larger variation in domain shape in the Tb‐Fe‐Co film compared to the Tb‐Co film. A careful observation based upon the image processing of domain...

A Boundary Oxidation Model for Amorphous Rare Earth-Transition Metal Films

Transmission electron microscopy and electron diffraction analysis of amorphous rare earth-transition metal alloy (RE-TM) films have been carried out to clarify the origin of experimentally obtained thickness dependence of their magnetic properties. It has been clarified that there is no islandlike structure even in a 5-nm-thick sample. It has also been clarified that there are an RE-oxide phase and a TM phase in samples with a thickness of below 10 nm. A boundary oxidation model for RE-TM films is proposed. The thickness of the boundary oxidation region (dB) and magnetization excluding the influence of the boundary oxidation region (Ms0) have been calculated based on this model. For films with an RE content of 27-28 at.%, the dB values were 10 to 20 nm, and the Ms0 values were 272 to 300 emu/cm3, which were 17% to 35% higher than the measured Ms values of 100-nm-thick films.

Numerical Analysis of Leakage Field Modulation for a Novel Direct Overwrite Medium

The numerical calculation of the leakage field in a novel laser-power modulation direct overwrite medium has been carried out. The medium had four functional layers: initializing layer, biasing layer, thermal isolating layer and storage layer. The leakage field applied to the storage layer was changed by the laser power. The degree of leakage field change and overwritable domain width, where the direction of an effective field applied to the storage layer could be modulated, were obtained as the figures of merit for overwriting performance. Si-N and Zr-O films were chosen as the thermal isolating layer in order to change the thermal response in the storage layer and the biasing layer. It has been found that the medium with a Si-N thermal isolating layer is suitable for overwriting and that leakage field modulation over 120 Oe was available within a domain width of 0.7 µm.

Experimental Examination of an Overwrite Method Utilizing Leakage Field Modulation by the Laser Power Level

A recently proposed novel single beam overwrite method was examined in order to prove the overwrite concept. The storage layer, the thermal control layer, the biasing layer, and the initializing layer were stacked on a glass substrate and were examined by a magneto-optical read/write tester. It was clear that the leakage field from the biasing layer was modulated by the laser power level and that an overwritable operating region was obtained by this leakage field modulation. The operating margin increased by increasing the linear velocity of the disk. An overwrite CNR of 35 dB was obtained in velocities above 8 m/s with a 20% completely erasing power margin.

Numerical Analysis of Magnetization Reversal in TbCo Magneto-Optical Recording Disks

Thermo-magnetically reversed domain sizes in TbCo magneto-optical disks have been numerically analyzed. The recorded domain radii were derived from calculations of the partial differentials of magnetic energies at domain walls, according to Huths model. Disk samples were prepared and the measured thermo-magnetic properties were used in calculations. A relative value for the domain wall energy was obtained using the mean field theory. Its absolute value was adjusted so that calculated and measured threshold recording powers coincided. Recorded domains in disk media were observed with an Ar laser scanning polarized light microscope. The radii of the domains were compared with calculated values. This numerical analysis yielded fairly good estimates for rather high powers, whereas the calculated radii were much smaller than observed values near the threshold recording power.

Recording Characteristics of Magnetooptical Media with Auxiliary Magnetic Layer

The purpose of this study is to investigate the leakage field from the auxiliary layer to the recording layer in an exchange-coupled multilayered magneto-optical medium. In order to estimate the leakage field, test media, in which the auxiliary layer was deposited on the recording layer with a nonmagnetic layer intervening, were prepared. The leakage field was determined as the difference in the threshold external fields for two different initial magnetization directions in recording tests. The experimental results were in good agreement with numerical calculations, in which single-domain nucleation was assumed. The leakage field was found to be proportional to the change in magnetization at the heated spot. It was also found that a leakage field of about 200 Oe is generated in the auxiliary layer with a change in magnetization of 150 emu/cc.