S. Gadetsky

Magneto‐optical recording on patterned substrates (invited)

Patterning of glass or plastic substrates in the form of shallow square patches is a promising method of increasing the storage density for magneto‐optical disks. The sidewalls of the patches pin the reverse‐magnetized domains that develop in these samples. Confinement of domains within the patch boundaries during thermomagnetic recording has also been demonstrated. We have measured polarization conversion of the incident light on the sidewalls of the patches; a method to reduce the amount of such polarization conversion is proposed in this article.

Effect of grooves on magnetization reversal in amorphous TbFeCo thin films

We have investigated the effect of grooves milled by argon ions in soda lime glass substrates on the magnetic behavior of amorphous TbFeCo films deposited onto these substrates. The domains are shown to expand along the grooves when the groove depth exceeds 10 nm. The effect originates from the difference in the coercivities of the film on the land and on the groove, as well as from the pinning of domain walls by the side-walls of the grooves. >

Oblique sputtering of amorphous TbFeCo thin films on glass substrates and the effect of deposition angle on perpendicular magnetic anisotropy

We measured the magnetic hysteresis loops for several obliquely deposited amorphous TbFeCo films. The experimental results show that the direction of the average magnetic anisotropy (i.e., the easy axis of magnetization) is no longer along the surface normal. With the help of computer simulations, we have quantified the effects of oblique deposition in terms of the deviations of local anisotropy directions from the surface normal. We also found that, with the increasing of the deposition angle, the compensation point shifts toward the Fe-rich side and the films become thinner.

Barkhausen jumps during domain wall motion in thin magneto‐optical films

A method with high spatial resolution is developed to study wall motion in thin magnetic films with perpendicular anisotropy. Barkhausen jumps during domain wall motion in amorphous TbFeCo films and polycrystalline Co/Pd multilayer films have been observed. The average distance between strong pinning sites in Co/Pd was found to be around 0.3–0.4 μm. Maximum pinning times as long as several seconds were observed. Magnitudes of major jumps in TbFeCo were around 0.7 μm.

Thermomagnetic recording in amorphous TbFeCo films on patterned substrates

Magnetization reversal and thermomagnetic recording in amorphous TbFeCo films on patterned glass substrates were studied. Two types of patterns were examined: 1/spl times/1 /spl mu/m/sup 2/ raised and lowered square patches. Pinning of the domain walls at the side-walls of the patches was observed. Thermomagnetic recording experiments confirm the ability of patterned substrates to confine recorded domains within boundaries defined by the side-walls.

Measurements of the magneto-optic Kerr effect and the extraordinary Hall effect on grooved glass substrates coated with amorphous TbFeCo

Kerr loops measured in the 0th, −1st, and −2nd diffraction order beams on deep magneto-optic gratings show constructive and destructive interference of the beams reflected from grooves and lands as a function of effective phase depths and relative widths of grooves and lands. Hall-effect measurements yielded coercivities of grooves, lands, and sidewalls at different angles of the applied field. Sidewall reversals appear clearly in Kerr loops measured in the various diffracted beams, with signal amplitude depending on groove depth and the angle between the sidewall and the diffracted beam.

Domain wall dynamics in Co/Pd multilayers

Domain wall dynamics in Co/Pd multilayered films having different thickness are studied. Saturation of the domain wall velocity is observed in films having from 10 to 50 Co/Pd bilayers. The saturation velocities and wall mobilities appeared to be dependent on total film thickness, but their ratio was independent of the thickness.

A dynamic study of domain formation mechanism during thermomagnetic recording based on micro-Hall effect measurements

A method for analyzing the dynamics of domain formation during the thermomagnetic recording process has been developed based on the extraordinary Hall effect. A magnetic domain is written at the center of a cross‐shaped magneto‐optical sample having an area of 5×5 μm2, and the Hall voltage is monitored during the recording process. As far as domain nucleation is concerned, we find that the temperature gradient around the transition region (i.e., the region whose temperature is between the critical temperature for magnetization reversal and the Curie point) is very important. Under the conditions of high power and short pulse‐width laser, a domain can form only during the cooling period. However, it is possible for a domain to form during the heating cycle under a low power, long pulse laser beam.

Observation of domains and grooves on MO disks with optical microscopy and image processing

Optical microscopy and image processing are integrated to form a nondestructive test system for imaging magnetic domains and groove structures. High-contrast images and quantitative localized analysis such as Kerr loops, coercivity, and Kerr rotation angle can be obtained from coupons as well as from MO disks.