Sm Addition to GdCo and TbFe Films for Magneto-Optical Memory
Introduction In order to improve the magnetic properties of rare earthtransition metal alloys being studied for magneto-optical memory media, we added Sm to GdTbFeCo (a quaternary alloy), to make a quinternary alloy. We already reported that both the Kerr rotation angle and the magnetic anisotropy increase with the addition of Sm [1]. In order to study the origin of these improvements, we added Sm to GdCo and TbFe (each a binary alloy) to make ternary alloys. We then investigated their magnetic and magneto-optical properties.
The thermo-magnetic writing and erasing properties and Kerr rotation angle of amorphous TbFe thin film
The compositional dependences of writing, erasing and reading properties of amorphous TbFe thin film were examined in detail. As a result, there was marked differences between Fe-rich and Tb-rich film. That is, the external magnetic field necessary for writing was generally weaker and less dependent on composition in Tb-rich film and the composition range where erasing could be performed by the field of the same intensity as in writing was wider in Tb-rich side. Kerr rotation angle was measured in two different methods and the scattering values between them were observed in Fe-rich film, while there was no significant difference in Tb-rich film. The origins of these compositional dependence were explained by the differences of temperature dependences of M s and H c besides the compositional dependences of rectangular ratio and M s itself. The effects of the adding third elements to TbFe in Kerr rotation angle and minimum writing laser power were also measured. As a result, it was found, among some elements examined in this study, that Sm had effects of not only decreasing writing power but also increasing Kerr rotation angle in some degree.
Dynamic Recording and Readout Characteristics of GdTbFe Using a Modified Magneto-Optical Disk Exerciser
Amorphous ternary GdTbFe alloy films with a Kerr rotation angle of 0.38°–0.41° were prepared by rf sputtering on glass disks with a diameter of 115 mm. Thermomagnetic recording and readout experiments were carried out on these disks using a modified magneto-optical disk exerciser. The bit density of a few tens Mb/cm2 and the carrier-to-noise ratio (C/N) of 38 dB at 2.048 Mb/s (NRZ) were attained. It was found that a smaller spot diameter is desirable for readout than that for recording. Furthermore, primitive measurements of bit error rate were made at 1.536 and 2.048 Mb/s (NRZ), and values of the order of 10-5 were obtained.