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For improvement in recording power sensitivity in overwritable magnetooptic media with exchange coupled trilayer (ECTL), it has been found necessary to decrease the saturation magnetization (M/sub s/) value for the control layer, as well as to reduce the Curie temperature (T/sub c/) value for the writing layer. Highly rare-earth (RE) rich GdNdFeCo film has been used to decrease the M/sub s/ value for the control layer, instead of ferromagnetic NdFeCo film. The media consists of a PC substrate, a SiN underlayer, a transition-metal-rich TbFe memory layer, a NdFeCo or highly RE-rich GdNdFeCo control layer, an RE-rich GdNdFeCo writing layer whose compensation temperature is 180 degrees C, and an SiN protective layer. By using the RE-rich GdNdFeCo control layer and the lower T/sub c/ writing layer, the recording power sensitivity was improved 1.5 times compared to the media with NdFeCo control layer without decreasing the carrier-to-noise ratio. >

The magnetic properties of Tb/FeCoTi multilayered films, prepared by two-source DC magnetron sputtering, have been investigated as a function of the layer thickness to improve the recording sensitivity of magnetooptical disks. For a fixed bilayer thickness ratio, the Curie temperature, T/sub c/, was strongly dependent on the Tb layer thickness and reached a maximum near 4 AA. The Kerr rotation theta /sub k/ is almost constant, independent of the Tb layer thickness. The effective composition shifts to the transition-metal-rich side with increase in Tb layer thickness, greater than 4 AA, made possible a pronounced reduction in T/sub c/ and effective composition adjustment, without decreasing theta /sub k/. Studies on recording characteristics revealed that recording sensitivity and bias magnetic fields are controlled by the Tb layer thickness, without sacrificing carrier-to-noise ratio. >

A systematic study of magnetooptical properties for four different varieties of the (Pr,Nd)-(Tb,Dy)-FeCo system, focusing on temperature and wavelength dependences of Kerr rotation theta /sub k/ for alloy films and multilayered films, was made. The same relation between Curie temperature T/sub c/ and theta /sub k/ at a 830-nm wavelength was obtained for (Pr,Nd)-(Tb,Dy)-FeCo and (Tb,Dy,GdTb)-FeCo alloy films where the Co to FeCo ratio was less than 20 at.%. It was found that in the range of 500 nm to 900 nm the absolute magnitude of theta /sub k/ for all quaternary systems was always less than that for Dy-FeCo. These results suggest that amorphous rare-earth-FeCo alloy films containing Nd or Pr are not superior to (Tb,Dy)-FeCo films in regard to recording sensitivity and recording density in magnetooptical disks. On the other hand, theta /sub k/ enhancement was observed for Nd-Dy-FeCo multilayered films. This theta /sub k/ enhancement is not caused by the addition of Nd, but is due to the effect of film microstructure on theta /sub k/. >

The electric resistance of sputtered TbFeCo has been measured at room temperature as a function of magnetic field perpendicular to the film plane. Two kinds of anomalous magnetoresistance have been observed. One is a magnetoresistance peak in the magnetization-reversal region. The other is a reversible change proportional to the applied magnetic field, appearing in the other region. The magnetoresistance peak agrees well with a curve calculated from an experimental Hall loop. The magnetoresistance peak is found to originate from magnetic domain walls. The linear magnetoresistance change for transition-metal-dominant samples appears in a direction opposite to that for rare-earth-dominant samples. It is explained in terms of the reversible orientation change in the non-S-state Tb magnetic moment, which is dispersed because of random magnetic anisotropy. >