Jai-young Kim

Effect of sputtering pressure on stacking fault density and perpendicular magnetic anisotropy of CoPt alloys

We report the effects of Ar sputtering pressure on perpendicular magnetic anisotropy in disordered CoPt alloys via the modulation of stacking fault density. The coercivity and anisotropy field of CoPt alloys are gradually enlarged with an increase in Ar sputtering pressure from 3 mTorr to 30 mTorr. Structural analyses using transmission electron microscopy, atomic force microscopy and x-ray reflectivity show that the structural properties of the samples, such as roughness or grain size, are not significantly changed by variations in Ar sputtering pressure. On the other hand, in-plane x-ray diffraction measurements reveal that the stacking fault density is reduced in films grown under higher pressure, and instead favors HCP stacking. Our results suggest that perpendicular magnetic anisotropy in CoPt alloys can be enhanced by the growth of the sample under a high Ar sputtering pressure, which decreases stacking fault density.

Fabrication, characterization, and testing of (111) FePt L1 0 for heat assisted magnetic recording

The fabrication, characterization and recording of granular FePt L10 (111) oriented media are discussed. The granular structure is obtained through the addition of SiO2 during the deposition. It exhibited grain sizes less than 10 nm on average after post annealing. The effect of adding SiO2 is examined in the following manner. The crystallographic structure is examined through X-ray diffraction. The microstructures of the grains are observed by transmission electron microscopy. Hysteresis loops were obtained with a custom built polar magneto optic Kerr effect magnetometer (PMOKE) with field range up to 20 kOe and a Quantum Design SQUID magnetometer with field capability up to 50 kOe. Heat assisted magnetic recording was performed utilizing a custom designed and built heat assisted magnetic recording spin stand. The heat assisted magnetic recording spin stand was utilized to examine incident laser power requirements along with applied magnetic flux density requirements for recording. Data was successfully recorded and readout on high anisotropy FePt L10 (111) media that was not writable with perpendicular magnetic recording techniques. Recording results indicate that due to the high Curie temperature and large magnetization, a large applied magnetic flux density and a high recording temperature are required for saturation recording.