Perpendicular Anisotropy and Direct Overwrite Performance in Rare Earth Transition Metal Amorphous Films.

The origins of anisotropy and the dependence of the single-layer direct overwrite process on physical parameters of rare earth-transition metal films for magneto-optical recording media have been studied. Origins of perpendicular anisotropy in rare earth transition metal films have been identified to be pair-ordering, inverse magnetostrictive, and single-ion anisotropy. Relative contributions from each component to the total anisotropy were determined and found to strongly depend upon deposition conditions (Ar sputtering pressure and deposition power) as well as material properties (composition) of the films. Inverse magnetostrictive and single-ion anisotropy contribute as much as 90% to the total anisotropy. Pair-ordering contributes only 10% to the total anisotropy. The single-ion anisotropy is believed to be due to the alignment of the long axes of the elliptical 4f electron orbits of rare earth ions perpendicular to the film to minimize the electrostatic energy between two rare earth ions lying next to each other. In addition, the thermal stability of these three anisotropy components was investigated as a function of argon sputtering pressure and Tb percentage. The effects which magnetization and coercivity have on the direct overwrite characteristics were studied. In this investigation, the magnetization of films was varied by changing the compensation temperature and the Curie temperature, independently. The coercivity was varied by depositing films with an underlayer of Si_3 N_4, different Ar pressures, and different Gd/Tb ratios. Direct overwrite characteristics which were investigated included minimum pulse widths to erase and to write certain sizes of domains, erasure margins, and erasable domain sizes. The minimum pulse width to erase domains was found to increase when the coercivity was increased. A decrease in the compensation temperature, which leads to an increase in the magnetization at high temperatures, causes the minimum erasure pulse width to increase and the largest erasable domain size to decrease. However, a decrease in the compensation temperature causes the writing pulse width to decrease. Magnetic and physical properties required to achieve wide erasure margins and short pulse widths to write domains were determined.