Ultrahigh-Density Storage Media in Hard Disk Drives

2 Ultrahigh-Density Storage Media in Hard Disk Drives 

Moritz and coworkers have studied the coupling between the dots obtained by deposition of Co/Pt multilayers on prepattemed Si substrates [3.122,123]. Two patterning process were compared (a) electron-beam lithography followed by direct RIE [3.124], and (b) nanoimprint lithography followed by lift-off and dry RIE of silicon [3.125,126]. Subsequent deposition of a magnetic material (Co—Pt) leads to arrays of singledomain dots with a perpendicular magnetization. 

By nanoimprinting, a dot size down to 30 nm in diameter with a pitch of 60 nm has been obtained. This 

When the substrate consists of an array of silicon pillars, the structural and magnetic properties obtained with the two deposition modes are quite different, as illustrated in Figs. 5.3-37 and 5.3-38 [3.123]. With normal deposition, a rough deposit made of Co, Pt, and CoPt alloy grains is observed (Fig. 5.3-37a), which induces a ferromagnetic coupling between adjacent dots (Fig. 5.3-38a) via the sidewalls and the magnetic deposit in the bottom of the trenches [3.122]. 

In contrast, when the Pt is deposited at oblique incidence, one sidewall of the dots is coated with antiferromagnetic CoO, whereas the other side consists of a Pt-rich PtCo alloy, which is nonmagnetic (Fig. 5.3-37b). In this latter case, no direct coupling be- 

Influence of the Angle of Deposition. In order for one to be able to use these arrays of magnetic dots as recording media, the dots should be weakly coupled so that the magnetization of one dot can be switched without affecting the magnetization of the neighboring dots. In the present example, the sputtered species 

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S.3.4.2 Ultrahigh-Density Storage Media in Hard Disk Drives... 

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