Katsuhiro Kaneko

Magnetic and magneto‐optical properties of Tb‐Fe‐Co amorphous films

Characteristics of Tb‐Fe‐Co amorphous films have been systematically investigated in order to optimize compositions suitable for magneto‐optical recording medium with high readout signal. In order to optimize alloy composition, Curie temperature TC and compensation temperature Tcomp are summarized as functions of both Tb and Co contents. Crystallization temperature Tx of Tb‐Fe‐Co amorphous films has been also measured to be about 400 °C and tends to increase with replacing Fe by either Co or Tb. To evaluate Tb‐Fe‐Co films as a magneto‐optical recording medium, carrier C and modulation noise Nmod (defined by the difference in noise before and after writing) are measured as a function of external field Hex. It is found that written bits of large Nmod show an irregular shape, while those of small Nmod are of regular one. To reduce Nmod and obtain high readout C/N, films with lower saturation magnetization Ms (that is, low demagnetization field) at just below writing temperature are preferred.

Perpendicular magnetic anisotropy of Tb‐Co amorphous films sputtered in H2‐added Ar gas

Very large perpendicular magnetic anisotropy has been observed in Tb‐Co amorphous films deposited by nonbiased rf sputtering using H2‐added Ar gas. As the hydrogen partial pressure of the gas increases, the perpendicular anisotropy constant Ku increases remarkably and rectangular Kerr hysteresis loop appears. For 10% H2, Ku reaches near 105 J/m3, which is sufficient to direct the magnetization perpendicular to the film plane. These films can be used as magneto‐optical recording media because of the relatively large Kerr rotation angle and coercive force. The mechanism of increasing Ku remains to be clarified.

Magnetic and Magneto-Optical Properties of TbFeCo Amorphous Films

The relationship between the magneto-optical characteristics and the medium noise of TbFeCo films is studied. The Ms changes with temperature in Fe-rich and Tb-rich films differ markedly. Magnetic inversions occurred at high temperatures in films with a large Ms, causing a demagnetizing field which left blank sections in the recorded bits and increased the playback noise. At normal temperatures, Tb-rich films have a small Ms and, as a result, less modulation noise.

Perpendicular Magnetic Anisotropy of Tb-Co Amorphous Films Sputtered In H 2 -Added Ar Gas

Tb-Co amorphous films are prime candidates for use as magneto-optical recording media, but the method commonly employed to induce a perpendicular magnetic anisotropy, bias sputtering, is not compatible with glass substrates. In this case RF sputtering is used in an H2-Ar gas mixture, without a substrate bias voltage, to form Tb-Co films. As the hydrogen partial pressure PH2 was increased, the film saturation magnetization Ms decreased, the uniaxial anisotropy constant Ku increased, and the Kerr hysteresis loop became more rectangular. For PH2 = 10 percent, samples had an extremely large positive anisotropy even when the Tb content was varied over a wide range.

Influence of Sputtering Ar Pressure on Characteristics of Tb-Co Amorphous Thain Films

Amorphous Tb-Co films were prepared by diode RF sputtering under various Ar gas pressures and without applying a bias voltage, which is known to induce a large perpendicular magnetic anisotropy. The coercive force, saturation magnetization, and perpendicular anisotropy energy were measured as functions of the Ar pressure, and it was found that at higher pressures a perpendicular magnetic anisotropy was induced. Measurements of the film density and oxygen-content indicated that a large perpendicular magnetic anisotropy is induced for high oxygen contents and low atomic packing densities.