Sputter Etching Effect on Magnetic Properties in TaOx/TbFeCo/Ag Layered Films
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ABSTRACT Sputter etching effect on magnetic properties was investigated in TaOx/TbFeCo/Ag layered films. With sputter etching, smooth interfaces of about lnm roughness were obtained. In films with smooth interfaces, magnetization was stabilized and magnetization reversal was sharpened at around the Curie temperature. As a result, recorded marks were stabilized, and the media became sensitive to the magnetic field for writing. 49dB was obtained as C/N even at 0.454m mark length, which is sufficient for digital recording.
INTRODUCTION Increment of recording density is required for magneto-optical, or MO, disk. Recording density of MO disk is limited by the spot size of a focussed laser beam which reads the recorded marks out. Since the spot size of the laser beam is proportional to its wavelength, laser with shorter wavelength such as blue laser must be applied to get smaller beam spot. The quality of MO disk is often evaluated by means of the C/N value. The C/N value is proportional to the figure of merit, FOM, which is defined by the product of the square root of reflectivity and the magnetic Kerr rotation angle. It is well-known that the FOM of an amorphous TbFeCo alloy, which is widely adopted as the current MO media, decreases with the shortening of wavelength.[1] Therefore, it is suggested that TbFeCo is difficult to be adopted as blue laser MO media, and many researchers are studying Co/Pt multi-layered films and garnets, which show large FOM at shorter wavelength. [1][2][3] Such media, however, need more complicated processes to be produced, and cost higher than the current media. The aim of the present study is to develop MO media with large FOM which can be produced in simple processes. In order to obtain a larger FOM, the reflectivity and the magnetic Kerr rotation angle were simulated using the optical constants of all the layers which constitute a MO disk. It is found that large FOM can be obtained when a material with a small refraction index n is adopted as the reflective layer instead of the current Al alloy. It is also found that only Ag has sufficiently small n at shorter wavelength and that TaOxlTbFeCo/Ag layered film can be one of the candidates for the blue laser MO media. Since smaller recording marks must be formed on the blue laser MO media than those on the current media, it is important to control the formation of magnetic domain precisely in the blue laser MO media. Therefore, we must control the magnetic property at around the Curie temperature, where magnetic domains are formed. Interface etching is one of the techniques to control magnetic property of media.[3][4] We have investigated the effect of sputter etching in TaOx/TbFeCo/Ag layered films on magnetic property at higher temperature and on MO recording performance.
EXPERIMENTAL PROCEDURE TaOx/TbFeCo/Ag layered films were fabricated on glass substrates using the DC magnetron sputtering method. 35nm thick amorphous TaOx layer was deposited by reactive sputtering of a Ta target. 20nm TbFeCo layer with 20at% Tb content was deposited b
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